The ultracool dwarf star TRAPPIST-1 hosts seven Earth-size transiting planets, some of which could
harbour liquid water on their surfaces. UV observations are essential to measure their high-energy
irradiation, and to search for photodissociated water escaping from their putative atmospheres. Our
new observations of TRAPPIST-1 Ly-α line during the transit of TRAPPIST-1c show an evolution of
the star emission over three months, preventing us from assessing the presence of an extended hydrogen
exosphere. Based on the current knowledge of the stellar irradiation, we investigated the likely history
of water loss in the system. Planets b to d might still be in a runaway phase, and planets within the
orbit of TRAPPIST-1g could have lost more than 20 Earth oceans after 8 Gyr of hydrodynamic escape.
However, TRAPPIST-1e to h might have lost less than 3 Earth oceans if hydrodynamic escape stopped
once they entered the habitable zone. We caution that these estimates remain limited by the large
uncertainty on the planet masses. They likely represent upper limits on the actual water loss because
our assumptions maximize the XUV-driven escape, while photodissociation in the upper atmospheres
should be the limiting process. Late-stage outgassing could also have contributed significant amounts
of water for the outer, more massive planets after they entered the habitable zone. While our results
suggest that the outer planets are the best candidates to search for water with the JWST, they also
highlight the need for theoretical studies and complementary observations in all wavelength domains
to determine the nature of the TRAPPIST-1 planets, and their potential habitability.
Keywords: planetary systems - Stars: individual: TRAPPIST-1
WHERE IS THE FLUX GOING? THE LONG-TERM PHOTOMETRIC VARIABILITY OF BOYAJIAN’S ...Sérgio Sacani
We present ∼ 800 days of photometric monitoring of Boyajian’s Star (KIC 8462852) from the AllSky
Automated Survey for Supernovae (ASAS-SN) and ∼ 4000 days of monitoring from the All Sky
Automated Survey (ASAS). We show that from 2015 to the present the brightness of Boyajian’s Star
has steadily decreased at a rate of 6.3 ± 1.4 mmag yr−1
, such that the star is now 1.5% fainter than it
was in February 2015. Moreover, the longer time baseline afforded by ASAS suggests that Boyajian’s
Star has also undergone two brightening episodes in the past 11 years, rather than only exhibiting a
monotonic decline. We analyze a sample of ∼ 1000 comparison stars of similar brightness located in
the same ASAS-SN field and demonstrate that the recent fading is significant at & 99.4% confidence.
The 2015 − 2017 dimming rate is consistent with that measured with Kepler data for the time period
from 2009 to 2013. This long-term variability is difficult to explain with any of the physical models
for the star’s behavior proposed to date
EXTINCTION AND THE DIMMING OF KIC 8462852Sérgio Sacani
To test alternative hypotheses for the behavior of KIC 8462852, we obtained measurements of the star
over a wide wavelength range from the UV to the mid-infrared from October 2015 through December
2016, using Swift, Spitzer and at AstroLAB IRIS. The star faded in a manner similar to the longterm
fading seen in Kepler data about 1400 days previously. The dimming rate for the entire period
reported is 22.1 ± 9.7 milli-mag yr−1
in the Swift wavebands, with amounts of 21.0 ± 4.5 mmag in
the groundbased B measurements, 14.0 ± 4.5 mmag in V , and 13.0 ± 4.5 in R, and a rate of 5.0 ± 1.2
mmag yr−1 averaged over the two warm Spitzer bands. Although the dimming is small, it is seen at
& 3 σ by three different observatories operating from the UV to the IR. The presence of long-term
secular dimming means that previous SED models of the star based on photometric measurements
taken years apart may not be accurate. We find that stellar models with Tef f = 7000 - 7100 K and
AV ∼ 0.73 best fit the Swift data from UV to optical. These models also show no excess in the
near-simultaneous Spitzer photometry at 3.6 and 4.5 µm, although a longer wavelength excess from
a substantial debris disk is still possible (e.g., as around Fomalhaut). The wavelength dependence of
the fading favors a relatively neutral color (i.e., RV & 5, but not flat across all the bands) compared
with the extinction law for the general ISM (RV = 3.1), suggesting that the dimming arises from
circumstellar material
Proper-motion age dating of the progeny of Nova Scorpii ad 1437Sérgio Sacani
‘Cataclysmic variables’ are binary star systems in which one
star of the pair is a white dwarf, and which often generate bright
and energetic stellar outbursts. Classical novae are one type of
outburst: when the white dwarf accretes enough matter from its
companion, the resulting hydrogen-rich atmospheric envelope
can host a runaway thermonuclear reaction that generates a rapid
brightening1–4. Achieving peak luminosities of up to one million
times that of the Sun5
, all classical novae are recurrent, on timescales
of months6
to millennia7
. During the century before and after an
eruption, the ‘novalike’ binary systems that give rise to classical
novae exhibit high rates of mass transfer to their white dwarfs8
.
Another type of outburst is the dwarf nova: these occur in binaries
that have stellar masses and periods indistinguishable from those
of novalikes9
but much lower mass-transfer rates10, when accretiondisk
instabilities11 drop matter onto the white dwarfs. The coexistence
at the same orbital period of novalike binaries and dwarf
novae—which are identical but for their widely varying accretion
rates—has been a longstanding puzzle9
. Here we report the recovery
of the binary star underlying the classical nova eruption of 11 March
ad 1437 (refs 12, 13), and independently confirm its age by propermotion
dating. We show that, almost 500 years after a classical-nova
event, the system exhibited dwarf-nova eruptions. The three other
oldest recovered classical novae14–16 display nova shells, but lack
firm post-eruption ages17,18, and are also dwarf novae at present.
We conclude that many old novae become dwarf novae for part of
the millennia between successive nova eruptions19,
The completeness-corrected rate of stellar encounters with the Sun from the f...Sérgio Sacani
I report on close encounters of stars to the Sun found in the first Gaia data release (GDR1). Combining Gaia astrometry with radial
velocities of around 320 000 stars drawn from various catalogues, I integrate orbits in a Galactic potential to identify those stars which
come within a few parsecs. Such encounters could influence the solar system, for example through gravitational perturbations of the
Oort cloud. 16 stars are found to come within 2 pc (although a few of these have dubious data). This is fewer than were found in a
similar study based on Hipparcos data, even though the present study has many more candidates. This is partly because I reject stars
with large radial velocity uncertainties (>10 km s−1
), and partly because of missing stars in GDR1 (especially at the bright end). The
closest encounter found is Gl 710, a K dwarf long-known to come close to the Sun in about 1.3 Myr. The Gaia astrometry predict
a much closer passage than pre-Gaia estimates, however: just 16 000 AU (90% confidence interval: 10 000–21 000 AU), which will
bring this star well within the Oort cloud. Using a simple model for the spatial, velocity, and luminosity distributions of stars, together
with an approximation of the observational selection function, I model the incompleteness of this Gaia-based search as a function
of the time and distance of closest approach. Applying this to a subset of the observed encounters (excluding duplicates and stars
with implausibly large velocities), I estimate the rate of stellar encounters within 5 pc averaged over the past and future 5 Myr to be
545±59 Myr−1
. Assuming a quadratic scaling of the rate within some encounter distance (which my model predicts), this corresponds
to 87 ± 9 Myr−1 within 2 pc. A more accurate analysis and assessment will be possible with future Gaia data releases.
Evidence for a_distant_giant_planet_in_the_solar_systemSérgio Sacani
A descoberta de um novo planeta, atualmente não é uma manchete que chama tanto assim a atenção das pessoas. Muito disso, graças ao Telescópio Espacial Kepler, que já descobriu quase 2000 exoplanetas e todo instante uma nova descoberta é anunciada, certo? Mais ou menos, a descoberta anunciada hoje, dia 20 de Janeiro de 2016, é um pouco diferente, pois não se trata de um exoplaneta, e sim de um novo planeta no Sistema Solar, e esse é um fato que intriga os astrônomos a muitos e muitos anos.
Porém, temos que ir com calma com esses anúncios. No artigo aceito para publicação no The Astronomical Journal (artigo no final do post), os autores, Mike Brown e Konstantin Batygin, do Instituto de Tecnologia da Califórnia, apresentaram o que eles dizem ser evidências circunstâncias fortes para a existência de um grande planeta ainda não descoberto, talvez, com uma massa 10 vezes a massa da Terra, orbitando os confins do nosso Sistema Solar, muito além da órbita de Plutão. Os cientistas inferiram sua presença, por meio de anomalias encontradas nas órbitas de seis objetos do chamado Cinturão de Kuiper.
O objeto, que os pesquisadores estão chamando de Planeta Nove, não chega muito perto do Sol, no ponto mais próximo da sua órbita ele fica a 30.5 bilhões de quilômetros, ou seja, cinco vezes a distância entre o Sol e Plutão. Apesar do seu grande tamanho, ele é muito apagado, e por isso ninguém até o momento conseguiu observá-lo.
Não existe ainda uma confirmação observacional da descoberta, mas as evidências são tão fortes que fizeram com que outros especialistas como Chad Trujilo do Observatório Gemini no Havaí e David Nesvorny, do Southwest Research Institute em Boulder no Colorado, ficassem impressionados e bem convencidos de que deve mesmo haver um grande planeta nas fronteiras da nossa vizinhança cósmica.
Large turbulent reservoirs of cold molecular gas around high-redshift starbur...Sérgio Sacani
Starburst galaxies at the peak of cosmic star formation1
are among
the most extreme star-forming engines in the Universe, producing
stars over about 100 million years (ref. 2). The star-formation
rates of these galaxies, which exceed 100 solar masses per year,
require large reservoirs of cold molecular gas3
to be delivered to
their cores, despite strong feedback from stars or active galactic
nuclei4,5
. Consequently, starburst galaxies are ideal for studying the
interplay between this feedback and the growth of a galaxy6
. The
methylidyne cation, CH+, is a most useful molecule for such studies
because it cannot form in cold gas without suprathermal energy
input, so its presence indicates dissipation of mechanical energy7–9
or strong ultraviolet irradiation10,11. Here we report the detection of
CH+ (J=1–0) emission and absorption lines in the spectra of six
lensed starburst galaxies12–15 at redshifts near 2.5. This line has
such a high critical density for excitation that it is emitted only in
very dense gas, and is absorbed in low-density gas10. We find that
the CH+ emission lines, which are broader than 1,000 kilometres
per second, originate in dense shock waves powered by hot galactic
winds. The CH+ absorption lines reveal highly turbulent reservoirs
of cool (about 100 kelvin), low-density gas, extending far (more than
10 kiloparsecs) outside the starburst galaxies (which have radii of
less than 1 kiloparsec). We show that the galactic winds sustain
turbulence in the 10-kiloparsec-scale environments of the galaxies,
processing these environments into multiphase, gravitationally
bound reservoirs. However, the mass outflow rates are found to be
insufficient to balance the star-formation rates. Another mass input
is therefore required for these reservoirs, which could be provided by
ongoing mergers16 or cold-stream accretion17,18. Our results suggest
that galactic feedback, coupled jointly to turbulence and gravity,
extends the starburst phase of a galaxy instead of quenching it
Evidence for reflected_lightfrom_the_most_eccentric_exoplanet_knownSérgio Sacani
Planets in highly eccentric orbits form a class of objects not seen within our Solar System. The most extreme case known amongst these objects is the planet orbiting HD 20782, with an orbital period of 597 days and an eccentricity of 0.96. Here we present new data and analysis for this system as part of the Transit Ephemeris Refinement and Monitoring Survey (TERMS). We obtained CHIRON spectra to perform an independent estimation of the fundamental stellar parameters. New radial velocities from AAT and PARAS observations during periastron passage greatly improve our knowledge of the eccentric nature of the orbit. The combined analysis of our Keplerian orbital and Hipparcos astrometry show that the inclination of the planetary orbit is > 1.22◦, ruling out stellar masses for the companion. Our long-term robotic photometry show that the star is extremely stable over long timescales. Photometric monitoring of the star during predicted transit and periastron times using MOST rule out a transit of the planet and reveal evidence of phase variations during periastron. These possible photometric phase variations may be caused by reflected light from the planet’s atmosphere and the dramatic change in star–planet separation surrounding the periastron passage.
A nearby yoiung_m_dwarf_with_wide_possibly_planetary_m_ass_companionSérgio Sacani
O objeto de massa planetária J2126, anteriormente pensado como sendo um planeta solitário, orbita sua estrela mãe na maior órbita já descoberta até agora no universo, de acordo com uma equipe de astrônomos liderada pelo Dr. Niall Deacon, da Universidade de Hertfordshire, no Reino Unido.
O J2126, cujo nome completo é 2MASS J21265040-8140293, tem cerca de 13 vezes a massa de Júpiter.
Sua órbita é de aproximadamente 6900 Unidades Astronômicas de distância da sua estrela, a TYC 9486-927-1, uma estrela ativa, de rotação rápida e classificada como sendo do tipo Anã-M.
Essa é uma órbita 6900 vezes maior que a distância da Terra ao Sol, ou seja, aproximadamente 1 trilhão de quilômetros. Nessa sua órbita, o planeta leva 900000 anos para completar uma volta ao redor da sua estrela.
WHERE IS THE FLUX GOING? THE LONG-TERM PHOTOMETRIC VARIABILITY OF BOYAJIAN’S ...Sérgio Sacani
We present ∼ 800 days of photometric monitoring of Boyajian’s Star (KIC 8462852) from the AllSky
Automated Survey for Supernovae (ASAS-SN) and ∼ 4000 days of monitoring from the All Sky
Automated Survey (ASAS). We show that from 2015 to the present the brightness of Boyajian’s Star
has steadily decreased at a rate of 6.3 ± 1.4 mmag yr−1
, such that the star is now 1.5% fainter than it
was in February 2015. Moreover, the longer time baseline afforded by ASAS suggests that Boyajian’s
Star has also undergone two brightening episodes in the past 11 years, rather than only exhibiting a
monotonic decline. We analyze a sample of ∼ 1000 comparison stars of similar brightness located in
the same ASAS-SN field and demonstrate that the recent fading is significant at & 99.4% confidence.
The 2015 − 2017 dimming rate is consistent with that measured with Kepler data for the time period
from 2009 to 2013. This long-term variability is difficult to explain with any of the physical models
for the star’s behavior proposed to date
EXTINCTION AND THE DIMMING OF KIC 8462852Sérgio Sacani
To test alternative hypotheses for the behavior of KIC 8462852, we obtained measurements of the star
over a wide wavelength range from the UV to the mid-infrared from October 2015 through December
2016, using Swift, Spitzer and at AstroLAB IRIS. The star faded in a manner similar to the longterm
fading seen in Kepler data about 1400 days previously. The dimming rate for the entire period
reported is 22.1 ± 9.7 milli-mag yr−1
in the Swift wavebands, with amounts of 21.0 ± 4.5 mmag in
the groundbased B measurements, 14.0 ± 4.5 mmag in V , and 13.0 ± 4.5 in R, and a rate of 5.0 ± 1.2
mmag yr−1 averaged over the two warm Spitzer bands. Although the dimming is small, it is seen at
& 3 σ by three different observatories operating from the UV to the IR. The presence of long-term
secular dimming means that previous SED models of the star based on photometric measurements
taken years apart may not be accurate. We find that stellar models with Tef f = 7000 - 7100 K and
AV ∼ 0.73 best fit the Swift data from UV to optical. These models also show no excess in the
near-simultaneous Spitzer photometry at 3.6 and 4.5 µm, although a longer wavelength excess from
a substantial debris disk is still possible (e.g., as around Fomalhaut). The wavelength dependence of
the fading favors a relatively neutral color (i.e., RV & 5, but not flat across all the bands) compared
with the extinction law for the general ISM (RV = 3.1), suggesting that the dimming arises from
circumstellar material
Proper-motion age dating of the progeny of Nova Scorpii ad 1437Sérgio Sacani
‘Cataclysmic variables’ are binary star systems in which one
star of the pair is a white dwarf, and which often generate bright
and energetic stellar outbursts. Classical novae are one type of
outburst: when the white dwarf accretes enough matter from its
companion, the resulting hydrogen-rich atmospheric envelope
can host a runaway thermonuclear reaction that generates a rapid
brightening1–4. Achieving peak luminosities of up to one million
times that of the Sun5
, all classical novae are recurrent, on timescales
of months6
to millennia7
. During the century before and after an
eruption, the ‘novalike’ binary systems that give rise to classical
novae exhibit high rates of mass transfer to their white dwarfs8
.
Another type of outburst is the dwarf nova: these occur in binaries
that have stellar masses and periods indistinguishable from those
of novalikes9
but much lower mass-transfer rates10, when accretiondisk
instabilities11 drop matter onto the white dwarfs. The coexistence
at the same orbital period of novalike binaries and dwarf
novae—which are identical but for their widely varying accretion
rates—has been a longstanding puzzle9
. Here we report the recovery
of the binary star underlying the classical nova eruption of 11 March
ad 1437 (refs 12, 13), and independently confirm its age by propermotion
dating. We show that, almost 500 years after a classical-nova
event, the system exhibited dwarf-nova eruptions. The three other
oldest recovered classical novae14–16 display nova shells, but lack
firm post-eruption ages17,18, and are also dwarf novae at present.
We conclude that many old novae become dwarf novae for part of
the millennia between successive nova eruptions19,
The completeness-corrected rate of stellar encounters with the Sun from the f...Sérgio Sacani
I report on close encounters of stars to the Sun found in the first Gaia data release (GDR1). Combining Gaia astrometry with radial
velocities of around 320 000 stars drawn from various catalogues, I integrate orbits in a Galactic potential to identify those stars which
come within a few parsecs. Such encounters could influence the solar system, for example through gravitational perturbations of the
Oort cloud. 16 stars are found to come within 2 pc (although a few of these have dubious data). This is fewer than were found in a
similar study based on Hipparcos data, even though the present study has many more candidates. This is partly because I reject stars
with large radial velocity uncertainties (>10 km s−1
), and partly because of missing stars in GDR1 (especially at the bright end). The
closest encounter found is Gl 710, a K dwarf long-known to come close to the Sun in about 1.3 Myr. The Gaia astrometry predict
a much closer passage than pre-Gaia estimates, however: just 16 000 AU (90% confidence interval: 10 000–21 000 AU), which will
bring this star well within the Oort cloud. Using a simple model for the spatial, velocity, and luminosity distributions of stars, together
with an approximation of the observational selection function, I model the incompleteness of this Gaia-based search as a function
of the time and distance of closest approach. Applying this to a subset of the observed encounters (excluding duplicates and stars
with implausibly large velocities), I estimate the rate of stellar encounters within 5 pc averaged over the past and future 5 Myr to be
545±59 Myr−1
. Assuming a quadratic scaling of the rate within some encounter distance (which my model predicts), this corresponds
to 87 ± 9 Myr−1 within 2 pc. A more accurate analysis and assessment will be possible with future Gaia data releases.
Evidence for a_distant_giant_planet_in_the_solar_systemSérgio Sacani
A descoberta de um novo planeta, atualmente não é uma manchete que chama tanto assim a atenção das pessoas. Muito disso, graças ao Telescópio Espacial Kepler, que já descobriu quase 2000 exoplanetas e todo instante uma nova descoberta é anunciada, certo? Mais ou menos, a descoberta anunciada hoje, dia 20 de Janeiro de 2016, é um pouco diferente, pois não se trata de um exoplaneta, e sim de um novo planeta no Sistema Solar, e esse é um fato que intriga os astrônomos a muitos e muitos anos.
Porém, temos que ir com calma com esses anúncios. No artigo aceito para publicação no The Astronomical Journal (artigo no final do post), os autores, Mike Brown e Konstantin Batygin, do Instituto de Tecnologia da Califórnia, apresentaram o que eles dizem ser evidências circunstâncias fortes para a existência de um grande planeta ainda não descoberto, talvez, com uma massa 10 vezes a massa da Terra, orbitando os confins do nosso Sistema Solar, muito além da órbita de Plutão. Os cientistas inferiram sua presença, por meio de anomalias encontradas nas órbitas de seis objetos do chamado Cinturão de Kuiper.
O objeto, que os pesquisadores estão chamando de Planeta Nove, não chega muito perto do Sol, no ponto mais próximo da sua órbita ele fica a 30.5 bilhões de quilômetros, ou seja, cinco vezes a distância entre o Sol e Plutão. Apesar do seu grande tamanho, ele é muito apagado, e por isso ninguém até o momento conseguiu observá-lo.
Não existe ainda uma confirmação observacional da descoberta, mas as evidências são tão fortes que fizeram com que outros especialistas como Chad Trujilo do Observatório Gemini no Havaí e David Nesvorny, do Southwest Research Institute em Boulder no Colorado, ficassem impressionados e bem convencidos de que deve mesmo haver um grande planeta nas fronteiras da nossa vizinhança cósmica.
Large turbulent reservoirs of cold molecular gas around high-redshift starbur...Sérgio Sacani
Starburst galaxies at the peak of cosmic star formation1
are among
the most extreme star-forming engines in the Universe, producing
stars over about 100 million years (ref. 2). The star-formation
rates of these galaxies, which exceed 100 solar masses per year,
require large reservoirs of cold molecular gas3
to be delivered to
their cores, despite strong feedback from stars or active galactic
nuclei4,5
. Consequently, starburst galaxies are ideal for studying the
interplay between this feedback and the growth of a galaxy6
. The
methylidyne cation, CH+, is a most useful molecule for such studies
because it cannot form in cold gas without suprathermal energy
input, so its presence indicates dissipation of mechanical energy7–9
or strong ultraviolet irradiation10,11. Here we report the detection of
CH+ (J=1–0) emission and absorption lines in the spectra of six
lensed starburst galaxies12–15 at redshifts near 2.5. This line has
such a high critical density for excitation that it is emitted only in
very dense gas, and is absorbed in low-density gas10. We find that
the CH+ emission lines, which are broader than 1,000 kilometres
per second, originate in dense shock waves powered by hot galactic
winds. The CH+ absorption lines reveal highly turbulent reservoirs
of cool (about 100 kelvin), low-density gas, extending far (more than
10 kiloparsecs) outside the starburst galaxies (which have radii of
less than 1 kiloparsec). We show that the galactic winds sustain
turbulence in the 10-kiloparsec-scale environments of the galaxies,
processing these environments into multiphase, gravitationally
bound reservoirs. However, the mass outflow rates are found to be
insufficient to balance the star-formation rates. Another mass input
is therefore required for these reservoirs, which could be provided by
ongoing mergers16 or cold-stream accretion17,18. Our results suggest
that galactic feedback, coupled jointly to turbulence and gravity,
extends the starburst phase of a galaxy instead of quenching it
Evidence for reflected_lightfrom_the_most_eccentric_exoplanet_knownSérgio Sacani
Planets in highly eccentric orbits form a class of objects not seen within our Solar System. The most extreme case known amongst these objects is the planet orbiting HD 20782, with an orbital period of 597 days and an eccentricity of 0.96. Here we present new data and analysis for this system as part of the Transit Ephemeris Refinement and Monitoring Survey (TERMS). We obtained CHIRON spectra to perform an independent estimation of the fundamental stellar parameters. New radial velocities from AAT and PARAS observations during periastron passage greatly improve our knowledge of the eccentric nature of the orbit. The combined analysis of our Keplerian orbital and Hipparcos astrometry show that the inclination of the planetary orbit is > 1.22◦, ruling out stellar masses for the companion. Our long-term robotic photometry show that the star is extremely stable over long timescales. Photometric monitoring of the star during predicted transit and periastron times using MOST rule out a transit of the planet and reveal evidence of phase variations during periastron. These possible photometric phase variations may be caused by reflected light from the planet’s atmosphere and the dramatic change in star–planet separation surrounding the periastron passage.
A nearby yoiung_m_dwarf_with_wide_possibly_planetary_m_ass_companionSérgio Sacani
O objeto de massa planetária J2126, anteriormente pensado como sendo um planeta solitário, orbita sua estrela mãe na maior órbita já descoberta até agora no universo, de acordo com uma equipe de astrônomos liderada pelo Dr. Niall Deacon, da Universidade de Hertfordshire, no Reino Unido.
O J2126, cujo nome completo é 2MASS J21265040-8140293, tem cerca de 13 vezes a massa de Júpiter.
Sua órbita é de aproximadamente 6900 Unidades Astronômicas de distância da sua estrela, a TYC 9486-927-1, uma estrela ativa, de rotação rápida e classificada como sendo do tipo Anã-M.
Essa é uma órbita 6900 vezes maior que a distância da Terra ao Sol, ou seja, aproximadamente 1 trilhão de quilômetros. Nessa sua órbita, o planeta leva 900000 anos para completar uma volta ao redor da sua estrela.
The puzzling source_in_ngc6388_a_possible_planetary_tidal_disruption_eventSérgio Sacani
Artigo descreve a descoberta da destruição de um planeta ao passar próximo a uma estrela do tipo anã branca presente dentro do aglomerado globular de estrelas NGC 6388. Para isso os astrônomos utilizaram um arsenal de telescópios.
Evidence for the_thermal_sunyaev-zeldovich_effect_associated_with_quasar_feed...Sérgio Sacani
Using a radio-quiet subsample of the Sloan Digital Sky Survey spectroscopic quasar
catalogue, spanning redshifts 0.5–3.5, we derive the mean millimetre and far-infrared
quasar spectral energy distributions (SEDs) via a stacking analysis of Atacama Cosmology
Telescope and Herschel-Spectral and Photometric Imaging REceiver data. We
constrain the form of the far-infrared emission and find 3σ–4σ evidence for the thermal
Sunyaev-Zel’dovich (SZ) effect, characteristic of a hot ionized gas component with
thermal energy (6.2 ± 1.7) × 1060 erg. This amount of thermal energy is greater than
expected assuming only hot gas in virial equilibrium with the dark matter haloes of
(1 − 5) × 1012h
−1M that these systems are expected to occupy, though the highest
quasar mass estimates found in the literature could explain a large fraction of this
energy. Our measurements are consistent with quasars depositing up to (14.5±3.3) τ
−1
8
per cent of their radiative energy into their circumgalactic environment if their typical
period of quasar activity is τ8 × 108 yr. For high quasar host masses, ∼ 1013h
−1M,
this percentage will be reduced. Furthermore, the uncertainty on this percentage is
only statistical and additional systematic uncertainties enter at the 40 per cent level.
The SEDs are dust dominated in all bands and we consider various models for dust
emission. While sufficiently complex dust models can obviate the SZ effect, the SZ
interpretation remains favoured at the 3σ–4σ level for most models.
Uma grande equipe de astrônomos registrou uma supernova extremamente luminosa numa galáxia massiva a cerca de 3.82 bilhões de anos-luz de distância.
A explosão recém-descoberta, denominada de ASASSN-15Ih, pertence à classe mais luminosa de supernovas, chamada de supernovas superluminosas.
"Ela parece ter originado numa grande galáxia, em contraste com a maioria das supernovas superluminosas, que normalmente se originam em galáxias anãs com formação de estrelas", disse o Dr. Subo Dong, do Kavli Institute for Astronomy and Astrophysics e coautor do artigo publicado na revista Science que descreve a descoberta.
"Nós estimamos o raio efetivo para a galáxia de 7830 anos-luz e uma massa estelar de 200 bilhões de massas solares".
Também conhecida como SN 2015L, a ASASSN-15lh é aproximadamente 200 vezes mais poderosa do que uma típica explosão de supernova do Tipo Ia, cerca de 570 bilhões de vezes mais brilhante do que o nosso Sol, e vinte vezes mais brilhante do que todas as estrelas na nossa galáxia combinadas.
We report the discovery of a new Kepler transiting circumbinary planet (CBP).
This latest addition to the still-small family of CBPs defies the current trend of known
short-period planets orbiting near the stability limit of binary stars. Unlike the previous
discoveries, the planet revolving around the eclipsing binary system Kepler-1647 has
a very long orbital period ( 1100 days) and was at conjunction only twice during
the Kepler mission lifetime. Due to the singular configuration of the system, Kepler-
1647b is not only the longest-period transiting CBP at the time of writing, but also one
of the longest-period transiting planets. With a radius of 1:060:01 RJup it is also the
largest CBP to date. The planet produced three transits in the light-curve of Kepler-
1647 (one of them during an eclipse, creating a syzygy) and measurably perturbed the
times of the stellar eclipses, allowing us to measure its mass to be 1:520:65 MJup.
The planet revolves around an 11-day period eclipsing binary consisting of two Solarmass
stars on a slightly inclined, mildly eccentric (ebin = 0:16), spin-synchronized
orbit. Despite having an orbital period three times longer than Earth’s, Kepler-1647b is
in the conservative habitable zone of the binary star throughout its orbit.
Beyond the Kuiper Belt Edge: New High Perihelion Trans-Neptunian Objects With...Sérgio Sacani
We are conducting a survey for distant solar system objects beyond the Kuiper
Belt edge ( 50 AU) with new wide-field cameras on the Subaru and CTIO tele-
scopes. We are interested in the orbits of objects that are decoupled from the
giant planet region in order to understand the structure of the outer solar sys-
tem, including whether a massive planet exists beyond a few hundred AU as first
reported in Trujillo and Sheppard (2014). In addition to discovering extreme
trans-Neptunian objects detailed elsewhere, we have found several objects with
high perihelia (q > 40 AU) that differ from the extreme and inner Oort cloud
objects due to their moderate semi-major axes (50 < a < 100 AU) and eccen-
tricities (e . 0.3). Newly discovered objects 2014 FZ71 and 2015 FJ345 have
the third and fourth highest perihelia known after Sedna and 2012 VP113, yet
their orbits are not nearly as eccentric or distant. We found several of these high
perihelion but moderate orbit objects and observe that they are mostly near Nep-
tune mean motion resonances and have significant inclinations (i > 20 degrees).
These moderate objects likely obtained their unusual orbits through combined
interactions with Neptune’s mean motion resonances and the Kozai resonance,
similar to the origin scenarios for 2004 XR190. We also find the distant 2008
ST291 has likely been modified by the MMR+KR mechanism through the 6:1
Neptune resonance. We discuss these moderately eccentric, distant objects along
with some other interesting low inclination outer classical belt objects like 2012
FH84 discovered in our ongoing survey.
We present spectroscopic observations of the nearby dwarf galaxy AGC 198691. This object is part
of the Survey of H I in Extremely Low-Mass Dwarfs (SHIELD) project, which is a multi-wavelength
study of galaxies with H I masses in the range of 106-107:2 M discovered by the ALFALFA survey.
We have obtained spectra of the lone H II region in AGC 198691 with the new high-throughput
KPNO Ohio State Multi-Object Spectrograph (KOSMOS) on the Mayall 4-m as well as with the Blue
Channel spectrograph on the MMT 6.5-m telescope. These observations enable the measurement of the
temperature-sensitive [O III]4363 line and hence the determination of a \direct" oxygen abundance
for AGC 198691. We nd this system to be an extremely metal-decient (XMD) system with an
oxygen abundance of 12+log(O/H) = 7.02 0.03, making AGC 198691 the lowest-abundance starforming
galaxy known in the local universe. Two of the ve lowest-abundance galaxies known have
been discovered by the ALFALFA blind H I survey; this high yield of XMD galaxies represents a
paradigm shift in the search for extremely metal-poor galaxies.
Probing the innermost_regions_of_agn_jets_and_their_magnetic_fields_with_radi...Sérgio Sacani
Desde 1974, observações feitas com o chamado Long Baseline Interferometry, ou VLBI, combinaram sinais de um objeto cósmico recebidos em diferentes rádio telescópios espalhados pelo globo para criar uma antena com o tamanho equivalente à maior separação entre elas. Isso fez com que fosse possível fazer imagens com uma nitidez sem precedentes, com uma resolução 1000 vezes melhor do que Hubble consegue na luz visível. Agora, uma equipe internacional de astrônomos quebrou todos os recordes combinando 15 rádio telescópios na Terra e a antena de rádio da missão RadioAstron, da agência espacial russa, na órbita da Terra. O trabalho, liderado pelo Instituto de Astrofísica de Andalucía, o IAA-CSIC, forneceu novas ideias sobre a natureza das galáxias ativas, onde um buraco negro extremamente massivo engole a matéria ao redor enquanto simultaneamente emite um par de jatos de partículas de alta energia e campos magnéticos a velocidades próximas da velocidade da luz.
Observações feitas no comprimento de onda das micro-ondas são essenciais para explorar esses jatos, já que os elétrons de alta energia se movendo em campos magnéticos são mais proficientes em produzir micro-ondas. Mas a maioria das galáxias ativas com jatos brilhantes estão a bilhões de anos-luz de distância da Terra, de modo que esses jatos são minúsculos no céu. Desse modo a alta resolução é essencial para observar esses jatos em ação e então revelar fenômenos como as ondas de choque e a turbulência que controla o quanto de luz é produzida num dado tempo. “Combinando pela primeira vez rádio telescópios na Terra com rádio telescópios no espaço, operando na máxima resolução, tem permitido que a nossa equipe crie uma antena que tem um tamanho equivalente a 8 vezes o diâmetro da Terra, correspondendo a 20 micro arcos de segundo”, disse José L; Gómez, o líder da equipe no Instituto de Astrofísica de Andalucía, IAA-CSIC.
Quase 900 galáxias próximas, porém escondidas, têm sido estudadas por uma equipe internacional de astrônomos, levando uma nova luz sobre o entendimento do Grande Atrator - uma concentração difusa de massa a 250 milhões de anos-luz de distância, que está puxando a nossa Via Láctea, e milhares de outras galáxias em sua direção.
Usando o Multibeam Receiver, instalado no rádio telescópio Parkes de 64 m, pertencente à instituição CSIRO na Austrália, a equipe foi capaz de ver através das estrelas e da poeira da nossa galáxia, vasculhando assim uma região inexplorada do espaço, conhecida pelos astrônomos como Zone of Avoidance (Zona de Anulação).
“Nós descobrimos 883 galáxias, um terço das quais nunca tinham sido vistas anteriormente”, disse o Professor Lister Staveley-Smith, membro da equipe, do ARC Centre of Excellence for All-sky Astrophysics, e da University of Western Australia, um dos nós do International Centre for Radio Astronomy Research.
The nonmagnetic nucleus_of_comet_67_p_churyumov_gerasimenkoSérgio Sacani
Artigo descreve como a sonda Rosetta e o módulo Philae descobriram que o cometa Churyumov-Gerasimenko não é magnetizado, contrariando uma teoria da formação do Sistema Solar.
Stellar-like objects with effective temperatures of 2700K and below are referred to as
20 "ultracool dwarfs"1. This heterogeneous group includes both extremely low-mass stars
21 and brown dwarfs (substellar objects not massive enough to sustain hydrogen fusion),
22 and represents about 15% of the stellar-like objects in the vicinity of the Sun2. Based on
23 the small masses and sizes of their protoplanetary disks3,4, core-accretion theory for
24 ultracool dwarfs predicts a large, but heretofore undetected, population of close-in
25 terrestrial planets5, ranging from metal-rich Mercury-sized planets6 to more hospitable
26 volatile-rich Earth-sized planets7. Here we report the discovery of three short-period
27 Earth-sized planets transiting an ultracool dwarf star 12 parsecs away. The inner two
28 planets receive four and two times the irradiation of Earth, respectively, placing them
29 close to the inner edge of the habitable zone of the star8. Eleven orbits remain possible
30 for the third planet based on our data, the most likely resulting in an irradiation
31 significantly smaller than Earth's. The infrared brightness of the host star combined
32 with its Jupiter-like size offer the possibility of constraining the composition and
33 thoroughly characterizing the atmospheric properties of the components of this nearby
34 planetary system, notably to detect potential biosignatures.
Periodic mass extinctions_and_the_planet_x_model_reconsideredSérgio Sacani
The 27 Myr periodicity in the fossil extinction record has been con-
firmed in modern data bases dating back 500 Myr, which is twice the time
interval of the original analysis from thirty years ago. The surprising regularity
of this period has been used to reject the Nemesis model. A second
model based on the sun’s vertical galactic oscillations has been challenged
on the basis of an inconsistency in period and phasing. The third astronomical
model originally proposed to explain the periodicity is the Planet
X model in which the period is associated with the perihelion precession
of the inclined orbit of a trans-Neptunian planet. Recently, and unrelated
to mass extinctions, a trans-Neptunian super-Earth planet has been proposed
to explain the observation that the inner Oort cloud objects Sedna
and 2012VP113 have perihelia that lie near the ecliptic plane. In this
Letter we reconsider the Planet X model in light of the confluence of the
modern palaeontological and outer solar system dynamical evidence.
Key Words: astrobiology - planets and satellites - Kuiper belt:
general - comets: general
We discovered two transient events in the Kepler eld with light curves that strongly suggest they
are type II-P supernovae. Using the fast cadence of the Kepler observations we precisely estimate
the rise time to maximum for KSN2011a and KSN2011d as 10.50:4 and 13.30:4 rest-frame days
respectively. Based on ts to idealized analytic models, we nd the progenitor radius of KSN2011a
(28020 R) to be signicantly smaller than that for KSN2011d (49020 R) but both have similar
explosion energies of 2.00:3 1051 erg.
The rising light curve of KSN2011d is an excellent match to that predicted by simple models of
exploding red supergiants (RSG). However, the early rise of KSN2011a is faster than the models
predict possibly due to the supernova shockwave moving into pre-existing wind or mass-loss from the
RSG. A mass loss rate of 10 4 M yr 1 from the RSG can explain the fast rise without impacting
the optical
ux at maximum light or the shape of the post-maximum light curve.
No shock breakout emission is seen in KSN2011a, but this is likely due to the circumstellar inter-
action suspected in the fast rising light curve. The early light curve of KSN2011d does show excess
emission consistent with model predictions of a shock breakout. This is the rst optical detection of
a shock breakout from a type II-P supernova.
Detection of solar_like_oscillations_in_relies_of_the_milk_way_asteroseismolo...Sérgio Sacani
Asteroseismic constraints on K giants make it possible to infer radii, masses and ages of tens
of thousands of field stars. Tests against independent estimates of these properties are however
scarce, especially in the metal-poor regime. Here, we report the detection of solar-like
oscillations in 8 stars belonging to the red-giant branch and red-horizontal branch of the globular
cluster M4. The detections were made in photometric observations from the K2 Mission
during its Campaign 2. Making use of independent constraints on the distance, we estimate
masses of the 8 stars by utilising different combinations of seismic and non-seismic inputs.
When introducing a correction to the Δν scaling relation as suggested by stellar models, for
RGB stars we find excellent agreement with the expected masses from isochrone fitting, and
with a distance modulus derived using independent methods. The offset with respect to independent
masses is lower, or comparable with, the uncertainties on the average RGB mass
(4 − 10%, depending on the combination of constraints used). Our results lend confidence to
asteroseismic masses in the metal poor regime. We note that a larger sample will be needed
to allow more stringent tests to be made of systematic uncertainties in all the observables
(both seismic and non-seismic), and to explore the properties of RHB stars, and of different
populations in the cluster.
Is there an_exoplanet_in_the_solar_systemSérgio Sacani
We investigate the prospects for the capture of the proposed Planet 9 from other
stars in the Sun’s birth cluster. Any capture scenario must satisfy three conditions:
the encounter must be more distant than ∼ 150 au to avoid perturbing the Kuiper
belt; the other star must have a wide-orbit planet (a & 100 au); the planet must be
captured onto an appropriate orbit to sculpt the orbital distribution of wide-orbit
Solar System bodies. Here we use N-body simulations to show that these criteria may
be simultaneously satisfied. In a few percent of slow close encounters in a cluster,
bodies are captured onto heliocentric, Planet 9-like orbits. During the ∼ 100 Myr
cluster phase, many stars are likely to host planets on highly-eccentric orbits with
apastron distances beyond 100 au if Neptune-sized planets are common and susceptible
to planet–planet scattering. While the existence of Planet 9 remains unproven, we
consider capture from one of the Sun’s young brethren a plausible route to explain such
an object’s orbit. Capture appears to predict a large population of Trans-Neptunian
Objects (TNOs) whose orbits are aligned with the captured planet, and we propose
that different formation mechanisms will be distinguishable based on their imprint on
the distribution of TNOs
The 19 Feb. 2016 Outburst of Comet 67P/CG: An ESA Rosetta Multi-Instrument StudySérgio Sacani
On 19 Feb. 2016 nine Rosetta instruments serendipitously observed an outburst of gas and dust
from the nucleus of comet 67P/Churyumov-Gerasimenko. Among these instruments were cameras
and spectrometers ranging from UV over visible to microwave wavelengths, in-situ gas, dust and
plasma instruments, and one dust collector. At 9:40 a dust cloud developed at the edge of an image
in the shadowed region of the nucleus. Over the next two hours the instruments recorded a signature
of the outburst that signicantly exceeded the background. The enhancement ranged from 50% of
the neutral gas density at Rosetta to factors >100 of the brightness of the coma near the nucleus.
Dust related phenomena (dust counts or brightness due to illuminated dust) showed the strongest
enhancements (factors >10). However, even the electron density at Rosetta increased by a factor 3
and consequently the spacecraft potential changed from 16V to 20V during the outburst. A
clear sequence of events was observed at the distance of Rosetta (34 km from the nucleus): within 15
minutes the Star Tracker camera detected fast particles ( 25 ms 1) while 100 m radius particles
were detected by the GIADA dust instrument 1 hour later at a speed of 6 ms 1. The slowest
were individual mm to cm sized grains observed by the OSIRIS cameras. Although the outburst
originated just outside the FOV of the instruments, the source region and the magnitude of the
outburst could be determined.
Magnetic field and_wind_of_kappa_ceti_towards_the_planetary_habitability_of_t...Sérgio Sacani
We report magnetic field measurements for κ
1 Cet, a proxy of the young Sun when life arose on Earth. We carry out an analysis
of the magnetic properties determined from spectropolarimetric observations and reconstruct its large-scale surface magnetic
field to derive the magnetic environment, stellar winds and particle flux permeating the interplanetary medium around κ
1 Cet.
Our results show a closer magnetosphere and mass-loss rate of M˙ = 9.7 × 10−13 M yr−1
, i.e., a factor 50 times larger than the
current solar wind mass-loss rate, resulting in a larger interaction via space weather disturbances between the stellar wind and
a hypothetical young-Earth analogue, potentially affecting the planet’s habitability. Interaction of the wind from the young Sun
with the planetary ancient magnetic field may have affected the young Earth and its life conditions.
The habitability of Proxima Centauri b - I. Irradiation, rotation and volatil...Sérgio Sacani
Proxima b is a planet with a minimum mass of 1.3 M⊕ orbiting within the habitable zone (HZ) of Proxima Centauri, a very low-mass,
active star and the Sun’s closest neighbor. Here we investigate a number of factors related to the potential habitability of Proxima b
and its ability to maintain liquid water on its surface. We set the stage by estimating the current high-energy irradiance of the planet
and show that the planet currently receives 30 times more EUV radiation than Earth and 250 times more X-rays. We compute the time
evolution of the star’s spectrum, which is essential for modeling the flux received over Proxima b’s lifetime. We also show that Proxima
b’s obliquity is likely null and its spin is either synchronous or in a 3:2 spin-orbit resonance, depending on the planet’s eccentricity and
level of triaxiality. Next we consider the evolution of Proxima b’s water inventory. We use our spectral energy distribution to compute
the hydrogen loss from the planet with an improved energy-limited escape formalism. Despite the high level of stellar activity we find
that Proxima b is likely to have lost less than an Earth ocean’s worth of hydrogen (EOH) before it reached the HZ 100–200 Myr after
its formation. The largest uncertainty in our work is the initial water budget, which is not constrained by planet formation models. We
conclude that Proxima b is a viable candidate habitable planet.
The puzzling source_in_ngc6388_a_possible_planetary_tidal_disruption_eventSérgio Sacani
Artigo descreve a descoberta da destruição de um planeta ao passar próximo a uma estrela do tipo anã branca presente dentro do aglomerado globular de estrelas NGC 6388. Para isso os astrônomos utilizaram um arsenal de telescópios.
Evidence for the_thermal_sunyaev-zeldovich_effect_associated_with_quasar_feed...Sérgio Sacani
Using a radio-quiet subsample of the Sloan Digital Sky Survey spectroscopic quasar
catalogue, spanning redshifts 0.5–3.5, we derive the mean millimetre and far-infrared
quasar spectral energy distributions (SEDs) via a stacking analysis of Atacama Cosmology
Telescope and Herschel-Spectral and Photometric Imaging REceiver data. We
constrain the form of the far-infrared emission and find 3σ–4σ evidence for the thermal
Sunyaev-Zel’dovich (SZ) effect, characteristic of a hot ionized gas component with
thermal energy (6.2 ± 1.7) × 1060 erg. This amount of thermal energy is greater than
expected assuming only hot gas in virial equilibrium with the dark matter haloes of
(1 − 5) × 1012h
−1M that these systems are expected to occupy, though the highest
quasar mass estimates found in the literature could explain a large fraction of this
energy. Our measurements are consistent with quasars depositing up to (14.5±3.3) τ
−1
8
per cent of their radiative energy into their circumgalactic environment if their typical
period of quasar activity is τ8 × 108 yr. For high quasar host masses, ∼ 1013h
−1M,
this percentage will be reduced. Furthermore, the uncertainty on this percentage is
only statistical and additional systematic uncertainties enter at the 40 per cent level.
The SEDs are dust dominated in all bands and we consider various models for dust
emission. While sufficiently complex dust models can obviate the SZ effect, the SZ
interpretation remains favoured at the 3σ–4σ level for most models.
Uma grande equipe de astrônomos registrou uma supernova extremamente luminosa numa galáxia massiva a cerca de 3.82 bilhões de anos-luz de distância.
A explosão recém-descoberta, denominada de ASASSN-15Ih, pertence à classe mais luminosa de supernovas, chamada de supernovas superluminosas.
"Ela parece ter originado numa grande galáxia, em contraste com a maioria das supernovas superluminosas, que normalmente se originam em galáxias anãs com formação de estrelas", disse o Dr. Subo Dong, do Kavli Institute for Astronomy and Astrophysics e coautor do artigo publicado na revista Science que descreve a descoberta.
"Nós estimamos o raio efetivo para a galáxia de 7830 anos-luz e uma massa estelar de 200 bilhões de massas solares".
Também conhecida como SN 2015L, a ASASSN-15lh é aproximadamente 200 vezes mais poderosa do que uma típica explosão de supernova do Tipo Ia, cerca de 570 bilhões de vezes mais brilhante do que o nosso Sol, e vinte vezes mais brilhante do que todas as estrelas na nossa galáxia combinadas.
We report the discovery of a new Kepler transiting circumbinary planet (CBP).
This latest addition to the still-small family of CBPs defies the current trend of known
short-period planets orbiting near the stability limit of binary stars. Unlike the previous
discoveries, the planet revolving around the eclipsing binary system Kepler-1647 has
a very long orbital period ( 1100 days) and was at conjunction only twice during
the Kepler mission lifetime. Due to the singular configuration of the system, Kepler-
1647b is not only the longest-period transiting CBP at the time of writing, but also one
of the longest-period transiting planets. With a radius of 1:060:01 RJup it is also the
largest CBP to date. The planet produced three transits in the light-curve of Kepler-
1647 (one of them during an eclipse, creating a syzygy) and measurably perturbed the
times of the stellar eclipses, allowing us to measure its mass to be 1:520:65 MJup.
The planet revolves around an 11-day period eclipsing binary consisting of two Solarmass
stars on a slightly inclined, mildly eccentric (ebin = 0:16), spin-synchronized
orbit. Despite having an orbital period three times longer than Earth’s, Kepler-1647b is
in the conservative habitable zone of the binary star throughout its orbit.
Beyond the Kuiper Belt Edge: New High Perihelion Trans-Neptunian Objects With...Sérgio Sacani
We are conducting a survey for distant solar system objects beyond the Kuiper
Belt edge ( 50 AU) with new wide-field cameras on the Subaru and CTIO tele-
scopes. We are interested in the orbits of objects that are decoupled from the
giant planet region in order to understand the structure of the outer solar sys-
tem, including whether a massive planet exists beyond a few hundred AU as first
reported in Trujillo and Sheppard (2014). In addition to discovering extreme
trans-Neptunian objects detailed elsewhere, we have found several objects with
high perihelia (q > 40 AU) that differ from the extreme and inner Oort cloud
objects due to their moderate semi-major axes (50 < a < 100 AU) and eccen-
tricities (e . 0.3). Newly discovered objects 2014 FZ71 and 2015 FJ345 have
the third and fourth highest perihelia known after Sedna and 2012 VP113, yet
their orbits are not nearly as eccentric or distant. We found several of these high
perihelion but moderate orbit objects and observe that they are mostly near Nep-
tune mean motion resonances and have significant inclinations (i > 20 degrees).
These moderate objects likely obtained their unusual orbits through combined
interactions with Neptune’s mean motion resonances and the Kozai resonance,
similar to the origin scenarios for 2004 XR190. We also find the distant 2008
ST291 has likely been modified by the MMR+KR mechanism through the 6:1
Neptune resonance. We discuss these moderately eccentric, distant objects along
with some other interesting low inclination outer classical belt objects like 2012
FH84 discovered in our ongoing survey.
We present spectroscopic observations of the nearby dwarf galaxy AGC 198691. This object is part
of the Survey of H I in Extremely Low-Mass Dwarfs (SHIELD) project, which is a multi-wavelength
study of galaxies with H I masses in the range of 106-107:2 M discovered by the ALFALFA survey.
We have obtained spectra of the lone H II region in AGC 198691 with the new high-throughput
KPNO Ohio State Multi-Object Spectrograph (KOSMOS) on the Mayall 4-m as well as with the Blue
Channel spectrograph on the MMT 6.5-m telescope. These observations enable the measurement of the
temperature-sensitive [O III]4363 line and hence the determination of a \direct" oxygen abundance
for AGC 198691. We nd this system to be an extremely metal-decient (XMD) system with an
oxygen abundance of 12+log(O/H) = 7.02 0.03, making AGC 198691 the lowest-abundance starforming
galaxy known in the local universe. Two of the ve lowest-abundance galaxies known have
been discovered by the ALFALFA blind H I survey; this high yield of XMD galaxies represents a
paradigm shift in the search for extremely metal-poor galaxies.
Probing the innermost_regions_of_agn_jets_and_their_magnetic_fields_with_radi...Sérgio Sacani
Desde 1974, observações feitas com o chamado Long Baseline Interferometry, ou VLBI, combinaram sinais de um objeto cósmico recebidos em diferentes rádio telescópios espalhados pelo globo para criar uma antena com o tamanho equivalente à maior separação entre elas. Isso fez com que fosse possível fazer imagens com uma nitidez sem precedentes, com uma resolução 1000 vezes melhor do que Hubble consegue na luz visível. Agora, uma equipe internacional de astrônomos quebrou todos os recordes combinando 15 rádio telescópios na Terra e a antena de rádio da missão RadioAstron, da agência espacial russa, na órbita da Terra. O trabalho, liderado pelo Instituto de Astrofísica de Andalucía, o IAA-CSIC, forneceu novas ideias sobre a natureza das galáxias ativas, onde um buraco negro extremamente massivo engole a matéria ao redor enquanto simultaneamente emite um par de jatos de partículas de alta energia e campos magnéticos a velocidades próximas da velocidade da luz.
Observações feitas no comprimento de onda das micro-ondas são essenciais para explorar esses jatos, já que os elétrons de alta energia se movendo em campos magnéticos são mais proficientes em produzir micro-ondas. Mas a maioria das galáxias ativas com jatos brilhantes estão a bilhões de anos-luz de distância da Terra, de modo que esses jatos são minúsculos no céu. Desse modo a alta resolução é essencial para observar esses jatos em ação e então revelar fenômenos como as ondas de choque e a turbulência que controla o quanto de luz é produzida num dado tempo. “Combinando pela primeira vez rádio telescópios na Terra com rádio telescópios no espaço, operando na máxima resolução, tem permitido que a nossa equipe crie uma antena que tem um tamanho equivalente a 8 vezes o diâmetro da Terra, correspondendo a 20 micro arcos de segundo”, disse José L; Gómez, o líder da equipe no Instituto de Astrofísica de Andalucía, IAA-CSIC.
Quase 900 galáxias próximas, porém escondidas, têm sido estudadas por uma equipe internacional de astrônomos, levando uma nova luz sobre o entendimento do Grande Atrator - uma concentração difusa de massa a 250 milhões de anos-luz de distância, que está puxando a nossa Via Láctea, e milhares de outras galáxias em sua direção.
Usando o Multibeam Receiver, instalado no rádio telescópio Parkes de 64 m, pertencente à instituição CSIRO na Austrália, a equipe foi capaz de ver através das estrelas e da poeira da nossa galáxia, vasculhando assim uma região inexplorada do espaço, conhecida pelos astrônomos como Zone of Avoidance (Zona de Anulação).
“Nós descobrimos 883 galáxias, um terço das quais nunca tinham sido vistas anteriormente”, disse o Professor Lister Staveley-Smith, membro da equipe, do ARC Centre of Excellence for All-sky Astrophysics, e da University of Western Australia, um dos nós do International Centre for Radio Astronomy Research.
The nonmagnetic nucleus_of_comet_67_p_churyumov_gerasimenkoSérgio Sacani
Artigo descreve como a sonda Rosetta e o módulo Philae descobriram que o cometa Churyumov-Gerasimenko não é magnetizado, contrariando uma teoria da formação do Sistema Solar.
Stellar-like objects with effective temperatures of 2700K and below are referred to as
20 "ultracool dwarfs"1. This heterogeneous group includes both extremely low-mass stars
21 and brown dwarfs (substellar objects not massive enough to sustain hydrogen fusion),
22 and represents about 15% of the stellar-like objects in the vicinity of the Sun2. Based on
23 the small masses and sizes of their protoplanetary disks3,4, core-accretion theory for
24 ultracool dwarfs predicts a large, but heretofore undetected, population of close-in
25 terrestrial planets5, ranging from metal-rich Mercury-sized planets6 to more hospitable
26 volatile-rich Earth-sized planets7. Here we report the discovery of three short-period
27 Earth-sized planets transiting an ultracool dwarf star 12 parsecs away. The inner two
28 planets receive four and two times the irradiation of Earth, respectively, placing them
29 close to the inner edge of the habitable zone of the star8. Eleven orbits remain possible
30 for the third planet based on our data, the most likely resulting in an irradiation
31 significantly smaller than Earth's. The infrared brightness of the host star combined
32 with its Jupiter-like size offer the possibility of constraining the composition and
33 thoroughly characterizing the atmospheric properties of the components of this nearby
34 planetary system, notably to detect potential biosignatures.
Periodic mass extinctions_and_the_planet_x_model_reconsideredSérgio Sacani
The 27 Myr periodicity in the fossil extinction record has been con-
firmed in modern data bases dating back 500 Myr, which is twice the time
interval of the original analysis from thirty years ago. The surprising regularity
of this period has been used to reject the Nemesis model. A second
model based on the sun’s vertical galactic oscillations has been challenged
on the basis of an inconsistency in period and phasing. The third astronomical
model originally proposed to explain the periodicity is the Planet
X model in which the period is associated with the perihelion precession
of the inclined orbit of a trans-Neptunian planet. Recently, and unrelated
to mass extinctions, a trans-Neptunian super-Earth planet has been proposed
to explain the observation that the inner Oort cloud objects Sedna
and 2012VP113 have perihelia that lie near the ecliptic plane. In this
Letter we reconsider the Planet X model in light of the confluence of the
modern palaeontological and outer solar system dynamical evidence.
Key Words: astrobiology - planets and satellites - Kuiper belt:
general - comets: general
We discovered two transient events in the Kepler eld with light curves that strongly suggest they
are type II-P supernovae. Using the fast cadence of the Kepler observations we precisely estimate
the rise time to maximum for KSN2011a and KSN2011d as 10.50:4 and 13.30:4 rest-frame days
respectively. Based on ts to idealized analytic models, we nd the progenitor radius of KSN2011a
(28020 R) to be signicantly smaller than that for KSN2011d (49020 R) but both have similar
explosion energies of 2.00:3 1051 erg.
The rising light curve of KSN2011d is an excellent match to that predicted by simple models of
exploding red supergiants (RSG). However, the early rise of KSN2011a is faster than the models
predict possibly due to the supernova shockwave moving into pre-existing wind or mass-loss from the
RSG. A mass loss rate of 10 4 M yr 1 from the RSG can explain the fast rise without impacting
the optical
ux at maximum light or the shape of the post-maximum light curve.
No shock breakout emission is seen in KSN2011a, but this is likely due to the circumstellar inter-
action suspected in the fast rising light curve. The early light curve of KSN2011d does show excess
emission consistent with model predictions of a shock breakout. This is the rst optical detection of
a shock breakout from a type II-P supernova.
Detection of solar_like_oscillations_in_relies_of_the_milk_way_asteroseismolo...Sérgio Sacani
Asteroseismic constraints on K giants make it possible to infer radii, masses and ages of tens
of thousands of field stars. Tests against independent estimates of these properties are however
scarce, especially in the metal-poor regime. Here, we report the detection of solar-like
oscillations in 8 stars belonging to the red-giant branch and red-horizontal branch of the globular
cluster M4. The detections were made in photometric observations from the K2 Mission
during its Campaign 2. Making use of independent constraints on the distance, we estimate
masses of the 8 stars by utilising different combinations of seismic and non-seismic inputs.
When introducing a correction to the Δν scaling relation as suggested by stellar models, for
RGB stars we find excellent agreement with the expected masses from isochrone fitting, and
with a distance modulus derived using independent methods. The offset with respect to independent
masses is lower, or comparable with, the uncertainties on the average RGB mass
(4 − 10%, depending on the combination of constraints used). Our results lend confidence to
asteroseismic masses in the metal poor regime. We note that a larger sample will be needed
to allow more stringent tests to be made of systematic uncertainties in all the observables
(both seismic and non-seismic), and to explore the properties of RHB stars, and of different
populations in the cluster.
Is there an_exoplanet_in_the_solar_systemSérgio Sacani
We investigate the prospects for the capture of the proposed Planet 9 from other
stars in the Sun’s birth cluster. Any capture scenario must satisfy three conditions:
the encounter must be more distant than ∼ 150 au to avoid perturbing the Kuiper
belt; the other star must have a wide-orbit planet (a & 100 au); the planet must be
captured onto an appropriate orbit to sculpt the orbital distribution of wide-orbit
Solar System bodies. Here we use N-body simulations to show that these criteria may
be simultaneously satisfied. In a few percent of slow close encounters in a cluster,
bodies are captured onto heliocentric, Planet 9-like orbits. During the ∼ 100 Myr
cluster phase, many stars are likely to host planets on highly-eccentric orbits with
apastron distances beyond 100 au if Neptune-sized planets are common and susceptible
to planet–planet scattering. While the existence of Planet 9 remains unproven, we
consider capture from one of the Sun’s young brethren a plausible route to explain such
an object’s orbit. Capture appears to predict a large population of Trans-Neptunian
Objects (TNOs) whose orbits are aligned with the captured planet, and we propose
that different formation mechanisms will be distinguishable based on their imprint on
the distribution of TNOs
The 19 Feb. 2016 Outburst of Comet 67P/CG: An ESA Rosetta Multi-Instrument StudySérgio Sacani
On 19 Feb. 2016 nine Rosetta instruments serendipitously observed an outburst of gas and dust
from the nucleus of comet 67P/Churyumov-Gerasimenko. Among these instruments were cameras
and spectrometers ranging from UV over visible to microwave wavelengths, in-situ gas, dust and
plasma instruments, and one dust collector. At 9:40 a dust cloud developed at the edge of an image
in the shadowed region of the nucleus. Over the next two hours the instruments recorded a signature
of the outburst that signicantly exceeded the background. The enhancement ranged from 50% of
the neutral gas density at Rosetta to factors >100 of the brightness of the coma near the nucleus.
Dust related phenomena (dust counts or brightness due to illuminated dust) showed the strongest
enhancements (factors >10). However, even the electron density at Rosetta increased by a factor 3
and consequently the spacecraft potential changed from 16V to 20V during the outburst. A
clear sequence of events was observed at the distance of Rosetta (34 km from the nucleus): within 15
minutes the Star Tracker camera detected fast particles ( 25 ms 1) while 100 m radius particles
were detected by the GIADA dust instrument 1 hour later at a speed of 6 ms 1. The slowest
were individual mm to cm sized grains observed by the OSIRIS cameras. Although the outburst
originated just outside the FOV of the instruments, the source region and the magnitude of the
outburst could be determined.
Magnetic field and_wind_of_kappa_ceti_towards_the_planetary_habitability_of_t...Sérgio Sacani
We report magnetic field measurements for κ
1 Cet, a proxy of the young Sun when life arose on Earth. We carry out an analysis
of the magnetic properties determined from spectropolarimetric observations and reconstruct its large-scale surface magnetic
field to derive the magnetic environment, stellar winds and particle flux permeating the interplanetary medium around κ
1 Cet.
Our results show a closer magnetosphere and mass-loss rate of M˙ = 9.7 × 10−13 M yr−1
, i.e., a factor 50 times larger than the
current solar wind mass-loss rate, resulting in a larger interaction via space weather disturbances between the stellar wind and
a hypothetical young-Earth analogue, potentially affecting the planet’s habitability. Interaction of the wind from the young Sun
with the planetary ancient magnetic field may have affected the young Earth and its life conditions.
The habitability of Proxima Centauri b - I. Irradiation, rotation and volatil...Sérgio Sacani
Proxima b is a planet with a minimum mass of 1.3 M⊕ orbiting within the habitable zone (HZ) of Proxima Centauri, a very low-mass,
active star and the Sun’s closest neighbor. Here we investigate a number of factors related to the potential habitability of Proxima b
and its ability to maintain liquid water on its surface. We set the stage by estimating the current high-energy irradiance of the planet
and show that the planet currently receives 30 times more EUV radiation than Earth and 250 times more X-rays. We compute the time
evolution of the star’s spectrum, which is essential for modeling the flux received over Proxima b’s lifetime. We also show that Proxima
b’s obliquity is likely null and its spin is either synchronous or in a 3:2 spin-orbit resonance, depending on the planet’s eccentricity and
level of triaxiality. Next we consider the evolution of Proxima b’s water inventory. We use our spectral energy distribution to compute
the hydrogen loss from the planet with an improved energy-limited escape formalism. Despite the high level of stellar activity we find
that Proxima b is likely to have lost less than an Earth ocean’s worth of hydrogen (EOH) before it reached the HZ 100–200 Myr after
its formation. The largest uncertainty in our work is the initial water budget, which is not constrained by planet formation models. We
conclude that Proxima b is a viable candidate habitable planet.
The Variable Detection of Atmospheric Escape around the Young, Hot Neptune AU...Sérgio Sacani
Photoevaporation is a potential explanation for several features within exoplanet demographics. Atmospheric escape
observed in young Neptune-sized exoplanets can provide insight into and characterize which mechanisms drive this
evolution and at what times they dominate. AU Mic b is one such exoplanet, slightly larger than Neptune (4.19 R⊕).
It closely orbits a 23 Myr pre-main-sequence M dwarf with an orbital period of 8.46 days. We obtained two visits of
AU Mic b at Lyα with Hubble Space Telescope (HST)/Space Telescope Imaging Spectrograph. One flare within the
first HST visit is characterized and removed from our search for a planetary transit. We present a nondetection in our
first visit, followed by the detection of escaping neutral hydrogen ahead of the planet in our second visit. The outflow
absorbed ∼30% of the star’s Lyα blue wing 2.5 hr before the planet’s white-light transit. We estimate that the
highest-velocity escaping material has a column density of 1013.96 cm−2 and is moving 61.26 km s−1 away from the
host star. AU Mic b’s large high-energy irradiation could photoionize its escaping neutral hydrogen in 44 minutes,
rendering it temporarily unobservable. Our time-variable Lyα transit ahead of AU Mic b could also be explained by
an intermediate stellar wind strength from AU Mic that shapes the escaping material into a leading tail. Future Lyα
observations of this system will confirm and characterize the unique variable nature of its Lyα transit, which,
combined with modeling, will tune the importance of stellar wind and photoionization.
Seven temperate terrestrial planets around the nearby ultracool dwarf star TR...Sérgio Sacani
One aim of modern astronomy is to detect temperate, Earth-like
exoplanets that are well suited for atmospheric characterization.
Recently, three Earth-sized planets were detected that transit (that
is, pass in front of) a star with a mass just eight per cent that of
the Sun, located 12 parsecs away1. The transiting configuration of
these planets, combined with the Jupiter-like size of their host star—
named TRAPPIST-1—makes possible in-depth studies of their
atmospheric properties with present-day and future astronomical
facilities1–3. Here we report the results of a photometric monitoring
campaign of that star from the ground and space. Our observations
reveal that at least seven planets with sizes and masses similar
to those of Earth revolve around TRAPPIST-1. The six inner
planets form a near-resonant chain, such that their orbital periods
(1.51, 2.42, 4.04, 6.06, 9.1 and 12.35 days) are near-ratios of small
integers. This architecture suggests that the planets formed farther
from the star and migrated inwards4,5. Moreover, the seven planets
have equilibrium temperatures low enough to make possible the
presence of liquid water on their surfaces6–8.
Predictions of the_atmospheric_composition_of_gj_1132_bSérgio Sacani
GJ 1132 b is a nearby Earth-sized exoplanet transiting an M dwarf, and is amongst the most highly
characterizable small exoplanets currently known. In this paper we study the interaction of a magma
ocean with a water-rich atmosphere on GJ 1132b and determine that it must have begun with more
than 5 wt% initial water in order to still retain a water-based atmosphere. We also determine the
amount of O2
that can build up in the atmosphere as a result of hydrogen dissociation and loss.
We find that the magma ocean absorbs at most ∼ 10% of the O2 produced, whereas more than
90% is lost to space through hydrodynamic drag. The most common outcome for GJ 1132 b from our
simulations is a tenuous atmosphere dominated by O2
, although for very large initial water abundances
atmospheres with several thousands of bars of O2
are possible. A substantial steam envelope would
indicate either the existence of an earlier H2
envelope or low XUV flux over the system’s lifetime. A
steam atmosphere would also imply the continued existence of a magma ocean on GJ 1132 b. Further
modeling is needed to study the evolution of CO2
or N2
-rich atmospheres on GJ 1132 b.
Phosphine gas in the cloud decks of VenusSérgio Sacani
Measurements of trace gases in planetary atmospheres help us explore chemical conditions different to those on Earth. Our
nearest neighbour, Venus, has cloud decks that are temperate but hyperacidic. Here we report the apparent presence of phosphine
(PH3) gas in Venus’s atmosphere, where any phosphorus should be in oxidized forms. Single-line millimetre-waveband
spectral detections (quality up to ~15σ) from the JCMT and ALMA telescopes have no other plausible identification. Atmospheric
PH3 at ~20 ppb abundance is inferred. The presence of PH3 is unexplained after exhaustive study of steady-state chemistry and
photochemical pathways, with no currently known abiotic production routes in Venus’s atmosphere, clouds, surface and subsurface,
or from lightning, volcanic or meteoritic delivery. PH3 could originate from unknown photochemistry or geochemistry,
or, by analogy with biological production of PH3 on Earth, from the presence of life. Other PH3 spectral features should be
sought, while in situ cloud and surface sampling could examine sources of this gas.
A continuum from_clear_to_cloudy_hot_jupiter_exoplanets_without_primordial_wa...Sérgio Sacani
Uma pesquisa de 10 exoplanetas quentes, do tamanho de Júpiter, conduzida com os telescópios Spitzer e Hubble da NASA levou uma equipe de astrônomos a resolverem um mistério que já durava algum tempo – por que alguns desses mundos têm menos água do que o esperado? A descoberta, oferece novas ideias sobre uma vasta coleção de atmosferas planetárias na nossa galáxia e sobre como os planetas são formados.
Dos quase 2000 planetas confirmados orbitando outras estrelas, um subconjunto deles são planetas gasosos com características similares ao planeta Júpiter, mas, como suas órbitas são muito próximas de suas estrelas, eles são terrivelmente quentes.
A proximidade desses exoplanetas das suas estrelas, faz com que seja difícil observá-los. Devido a essa dificuldade, o Hubble só conseguiu explorar poucos desses exoplanetas, chamados de Júpiteres Quentes, no passado. Esses estudos iniciais descobriram que alguns planetas possuem menos água do que era previsto pelos modelos atmosféricos.
Uma equipe internacional de astrônomos tem atacado o problema fazendo o maior catálogo espectroscópico de atmosferas de exoplanetas até o momento. Todos os planetas no catálogo seguem órbitas orientadas de modo que o planeta passa em frente da estrela quando visto da Terra. Devido a esse trânsito, parte da luz da estrela viaja pela atmosfera externa do exoplaneta. “A atmosfera deixa sua impressão digital única na luz da estrela, que nós podemos estudar, quando ela chega até nós”, explicou a coautora Hannah Wakeford, do Goddard Space Flight Center da NASA , em Greenbelt, Maryland.
Radial velocity monitoring has found the signature of a Msin i = 1:3 M planet located within the Habitable Zone of Proxima
Centauri, the Sun’s closest neighbor (Anglada-Escudé et al. 2016). Despite a hotter past and an active host star the planet Proxima b
could have retained enough volatiles to sustain surface habitability (Ribas et al. 2016). Here we use a 3D Global Climate Model (GCM)
to simulate Proxima b’s atmosphere and water cycle for its two likely rotation modes (the 1:1 and 3:2 spin-orbit resonances) while
varying the unconstrained surface water inventory and atmospheric greenhouse eect (represented here with a CO2-N2 atmosphere.)
We find that a broad range of atmospheric compositions can allow surface liquid water. On a tidally-locked planet with a surface water
inventory larger than 0.6 Earth ocean, liquid water is always present (assuming 1 bar of N2), at least in the substellar region. Liquid
water covers the whole planet for CO2 partial pressures & 1 bar. For smaller water inventories, water can be trapped on the night side,
forming either glaciers or lakes, depending on the amount of greenhouse gases. With a non-synchronous rotation, a minimum CO2
pressure of 10 mbar (assuming 1 bar of N2) is required to avoid falling into a completely frozen snowball state if water is abundant.
If the planet is dryer, 0.5 bar of CO2 would suce to prevent the trapping of any arbitrary small water inventory into polar ice
caps. More generally, any low-obliquity planet within the classical habitable zone of its star should be in one of the climate regimes
discussed here.
We use our GCM to produce reflection/emission spectra and phase curves for the dierent rotations and surface volatile inventories.
We find that atmospheric characterization will be possible by direct imaging with forthcoming large telescopes thanks to an angular
separation of 7=D at 1 m (with the E-ELT) and a contrast of 10 7. The magnitude of the planet will allow for high-resolution
spectroscopy and the search for molecular signatures, including H2O, O2, and CO2.
The observation of thermal phase curves, although challenging, can be attempted with JWST, thanks to a contrast of 210 5 at 10 m.
Proxima b will also be an exceptional target for future IR interferometers. Within a decade it will be possible to image Proxima b and
possibly determine whether this exoplanet’s surface is habitable.
Exomoons & Exorings with the Habitable Worlds Observatory I: On the Detection...Sérgio Sacani
The highest priority recommendation of the Astro2020 Decadal Survey for space-based astronomy
was the construction of an observatory capable of characterizing habitable worlds. In this paper series
we explore the detectability of and interference from exomoons and exorings serendipitously observed
with the proposed Habitable Worlds Observatory (HWO) as it seeks to characterize exoplanets, starting
in this manuscript with Earth-Moon analog mutual events. Unlike transits, which only occur in systems
viewed near edge-on, shadow (i.e., solar eclipse) and lunar eclipse mutual events occur in almost every
star-planet-moon system. The cadence of these events can vary widely from ∼yearly to multiple events
per day, as was the case in our younger Earth-Moon system. Leveraging previous space-based (EPOXI)
lightcurves of a Moon transit and performance predictions from the LUVOIR-B concept, we derive
the detectability of Moon analogs with HWO. We determine that Earth-Moon analogs are detectable
with observation of ∼2-20 mutual events for systems within 10 pc, and larger moons should remain
detectable out to 20 pc. We explore the extent to which exomoon mutual events can mimic planet
features and weather. We find that HWO wavelength coverage in the near-IR, specifically in the 1.4 µm
water band where large moons can outshine their host planet, will aid in differentiating exomoon signals
from exoplanet variability. Finally, we predict that exomoons formed through collision processes akin
to our Moon are more likely to be detected in younger systems, where shorter orbital periods and
favorable geometry enhance the probability and frequency of mutual events.
Two super-Earths at the edge of the habitable zone of the nearby M dwarf TOI-...Sérgio Sacani
The main scientific goal of TESS is to find planets smaller than Neptune around stars bright enough to allow further characterization studies. Given
our current instrumentation and detection biases, M dwarfs are prime targets to search for small planets that are in (or nearby) the habitable zone
of their host star. Here we use photometric observations and CARMENES radial velocity measurements to validate a pair of transiting planet
candidates found by TESS. The data was fitted simultaneously using a Bayesian MCMC procedure taking into account the stellar variability
present in the photometric and spectroscopic time series. We confirm the planetary origin of the two transiting candidates orbiting around TOI-
2095 (TIC 235678745). The star is a nearby M dwarf (d = 41:90 0:03 pc, Te = 3759 87 K, V = 12:6 mag) with a stellar mass and radius
of M? = 0:44 0:02 M and R? = 0:44 0:02 R, respectively. The planetary system is composed of two transiting planets: TOI-2095b with an
orbital period of Pb = 17:66484 (7 105) days and TOI-2095c with Pc = 28:17232 (14 105) days. Both planets have similar sizes with
Rb = 1:250:07 R and Rc = 1:330:08 R for planet b and c, respectively.We put upper limits on the masses of these objects with Mb < 4:1 M
for the inner and Mc < 7:4 M for the outer planet (95% confidence level). These two planets present equilibrium temperatures in the range of 300
- 350 K and are close to the inner edge of the habitable zone of their star.
Hot Earth or Young Venus? A nearby transiting rocky planet mysterySérgio Sacani
Venus and Earth provide astonishingly different views of the evolution of a rocky planet, raising the question of why these two rock y worlds evolv ed so differently. The recently disco v ered transiting Super-Earth LP 890-9c (TOI-4306c, SPECULOOS-2c) is a key to the question. It circles a nearby M6V star in 8.46 d. LP890-9c receives similar flux as modern Earth, which puts it very close to the inner edge of the Habitable Zone (HZ), where models differ strongly in their prediction of how long rocky planets can hold onto their water. We model the atmosphere of a hot LP890-9c at the inner edge of the HZ, where the planet could sustain several very different environments. The resulting transmission spectra differ considerably between a hot, wet exo-Earth, a steamy planet caught in a runaway greenhouse, and an exo-Venus. Distinguishing these scenarios from the planet’s spectra will provide critical new insights into the evolution of hot terrestrial planets into exo-Venus. Our model and spectra are available online as a tool to plan observations. They show that observing LP890-9c can provide key insights into the evolution of a rocky planet at the inner edge of the HZ as well as the long-term future of Earth.
Observation of Io’s Resurfacing via Plume Deposition Using Ground-based Adapt...Sérgio Sacani
Since volcanic activity was first discovered on Io from Voyager images in 1979, changes
on Io’s surface have been monitored from both spacecraft and ground-based telescopes.
Here, we present the highest spatial resolution images of Io ever obtained from a groundbased telescope. These images, acquired by the SHARK-VIS instrument on the Large
Binocular Telescope, show evidence of a major resurfacing event on Io’s trailing hemisphere. When compared to the most recent spacecraft images, the SHARK-VIS images
show that a plume deposit from a powerful eruption at Pillan Patera has covered part
of the long-lived Pele plume deposit. Although this type of resurfacing event may be common on Io, few have been detected due to the rarity of spacecraft visits and the previously low spatial resolution available from Earth-based telescopes. The SHARK-VIS instrument ushers in a new era of high resolution imaging of Io’s surface using adaptive
optics at visible wavelengths.
Earliest Galaxies in the JADES Origins Field: Luminosity Function and Cosmic ...Sérgio Sacani
We characterize the earliest galaxy population in the JADES Origins Field (JOF), the deepest
imaging field observed with JWST. We make use of the ancillary Hubble optical images (5 filters
spanning 0.4−0.9µm) and novel JWST images with 14 filters spanning 0.8−5µm, including 7 mediumband filters, and reaching total exposure times of up to 46 hours per filter. We combine all our data
at > 2.3µm to construct an ultradeep image, reaching as deep as ≈ 31.4 AB mag in the stack and
30.3-31.0 AB mag (5σ, r = 0.1” circular aperture) in individual filters. We measure photometric
redshifts and use robust selection criteria to identify a sample of eight galaxy candidates at redshifts
z = 11.5 − 15. These objects show compact half-light radii of R1/2 ∼ 50 − 200pc, stellar masses of
M⋆ ∼ 107−108M⊙, and star-formation rates of SFR ∼ 0.1−1 M⊙ yr−1
. Our search finds no candidates
at 15 < z < 20, placing upper limits at these redshifts. We develop a forward modeling approach to
infer the properties of the evolving luminosity function without binning in redshift or luminosity that
marginalizes over the photometric redshift uncertainty of our candidate galaxies and incorporates the
impact of non-detections. We find a z = 12 luminosity function in good agreement with prior results,
and that the luminosity function normalization and UV luminosity density decline by a factor of ∼ 2.5
from z = 12 to z = 14. We discuss the possible implications of our results in the context of theoretical
models for evolution of the dark matter halo mass function.
THE IMPORTANCE OF MARTIAN ATMOSPHERE SAMPLE RETURN.Sérgio Sacani
The return of a sample of near-surface atmosphere from Mars would facilitate answers to several first-order science questions surrounding the formation and evolution of the planet. One of the important aspects of terrestrial planet formation in general is the role that primary atmospheres played in influencing the chemistry and structure of the planets and their antecedents. Studies of the martian atmosphere can be used to investigate the role of a primary atmosphere in its history. Atmosphere samples would also inform our understanding of the near-surface chemistry of the planet, and ultimately the prospects for life. High-precision isotopic analyses of constituent gases are needed to address these questions, requiring that the analyses are made on returned samples rather than in situ.
Multi-source connectivity as the driver of solar wind variability in the heli...Sérgio Sacani
The ambient solar wind that flls the heliosphere originates from multiple
sources in the solar corona and is highly structured. It is often described
as high-speed, relatively homogeneous, plasma streams from coronal
holes and slow-speed, highly variable, streams whose source regions are
under debate. A key goal of ESA/NASA’s Solar Orbiter mission is to identify
solar wind sources and understand what drives the complexity seen in the
heliosphere. By combining magnetic feld modelling and spectroscopic
techniques with high-resolution observations and measurements, we show
that the solar wind variability detected in situ by Solar Orbiter in March
2022 is driven by spatio-temporal changes in the magnetic connectivity to
multiple sources in the solar atmosphere. The magnetic feld footpoints
connected to the spacecraft moved from the boundaries of a coronal hole
to one active region (12961) and then across to another region (12957). This
is refected in the in situ measurements, which show the transition from fast
to highly Alfvénic then to slow solar wind that is disrupted by the arrival of
a coronal mass ejection. Our results describe solar wind variability at 0.5 au
but are applicable to near-Earth observatories.
Gliese 12 b: A Temperate Earth-sized Planet at 12 pc Ideal for Atmospheric Tr...Sérgio Sacani
Recent discoveries of Earth-sized planets transiting nearby M dwarfs have made it possible to characterize the
atmospheres of terrestrial planets via follow-up spectroscopic observations. However, the number of such planets
receiving low insolation is still small, limiting our ability to understand the diversity of the atmospheric
composition and climates of temperate terrestrial planets. We report the discovery of an Earth-sized planet
transiting the nearby (12 pc) inactive M3.0 dwarf Gliese 12 (TOI-6251) with an orbital period (Porb) of 12.76 days.
The planet, Gliese 12 b, was initially identified as a candidate with an ambiguous Porb from TESS data. We
confirmed the transit signal and Porb using ground-based photometry with MuSCAT2 and MuSCAT3, and
validated the planetary nature of the signal using high-resolution images from Gemini/NIRI and Keck/NIRC2 as
well as radial velocity (RV) measurements from the InfraRed Doppler instrument on the Subaru 8.2 m telescope
and from CARMENES on the CAHA 3.5 m telescope. X-ray observations with XMM-Newton showed the host
star is inactive, with an X-ray-to-bolometric luminosity ratio of log 5.7 L L X bol » - . Joint analysis of the light
curves and RV measurements revealed that Gliese 12 b has a radius of 0.96 ± 0.05 R⊕,a3σ mass upper limit of
3.9 M⊕, and an equilibrium temperature of 315 ± 6 K assuming zero albedo. The transmission spectroscopy metric
(TSM) value of Gliese 12 b is close to the TSM values of the TRAPPIST-1 planets, adding Gliese 12 b to the small
list of potentially terrestrial, temperate planets amenable to atmospheric characterization with JWST.
Gliese 12 b, a temperate Earth-sized planet at 12 parsecs discovered with TES...Sérgio Sacani
We report on the discovery of Gliese 12 b, the nearest transiting temperate, Earth-sized planet found to date. Gliese 12 is a
bright (V = 12.6 mag, K = 7.8 mag) metal-poor M4V star only 12.162 ± 0.005 pc away from the Solar system with one of the
lowest stellar activity levels known for M-dwarfs. A planet candidate was detected by TESS based on only 3 transits in sectors
42, 43, and 57, with an ambiguity in the orbital period due to observational gaps. We performed follow-up transit observations
with CHEOPS and ground-based photometry with MINERVA-Australis, SPECULOOS, and Purple Mountain Observatory,
as well as further TESS observations in sector 70. We statistically validate Gliese 12 b as a planet with an orbital period of
12.76144 ± 0.00006 d and a radius of 1.0 ± 0.1 R⊕, resulting in an equilibrium temperature of ∼315 K. Gliese 12 b has excellent
future prospects for precise mass measurement, which may inform how planetary internal structure is affected by the stellar
compositional environment. Gliese 12 b also represents one of the best targets to study whether Earth-like planets orbiting cool
stars can retain their atmospheres, a crucial step to advance our understanding of habitability on Earth and across the galaxy.
The importance of continents, oceans and plate tectonics for the evolution of...Sérgio Sacani
Within the uncertainties of involved astronomical and biological parameters, the Drake Equation
typically predicts that there should be many exoplanets in our galaxy hosting active, communicative
civilizations (ACCs). These optimistic calculations are however not supported by evidence, which is
often referred to as the Fermi Paradox. Here, we elaborate on this long-standing enigma by showing
the importance of planetary tectonic style for biological evolution. We summarize growing evidence
that a prolonged transition from Mesoproterozoic active single lid tectonics (1.6 to 1.0 Ga) to modern
plate tectonics occurred in the Neoproterozoic Era (1.0 to 0.541 Ga), which dramatically accelerated
emergence and evolution of complex species. We further suggest that both continents and oceans
are required for ACCs because early evolution of simple life must happen in water but late evolution
of advanced life capable of creating technology must happen on land. We resolve the Fermi Paradox
(1) by adding two additional terms to the Drake Equation: foc
(the fraction of habitable exoplanets
with significant continents and oceans) and fpt
(the fraction of habitable exoplanets with significant
continents and oceans that have had plate tectonics operating for at least 0.5 Ga); and (2) by
demonstrating that the product of foc
and fpt
is very small (< 0.00003–0.002). We propose that the lack
of evidence for ACCs reflects the scarcity of long-lived plate tectonics and/or continents and oceans on
exoplanets with primitive life.
A Giant Impact Origin for the First Subduction on EarthSérgio Sacani
Hadean zircons provide a potential record of Earth's earliest subduction 4.3 billion years ago. Itremains enigmatic how subduction could be initiated so soon after the presumably Moon‐forming giant impact(MGI). Earlier studies found an increase in Earth's core‐mantle boundary (CMB) temperature due to theaccumulation of the impactor's core, and our recent work shows Earth's lower mantle remains largely solid, withsome of the impactor's mantle potentially surviving as the large low‐shear velocity provinces (LLSVPs). Here,we show that a hot post‐impact CMB drives the initiation of strong mantle plumes that can induce subductioninitiation ∼200 Myr after the MGI. 2D and 3D thermomechanical computations show that a high CMBtemperature is the primary factor triggering early subduction, with enrichment of heat‐producing elements inLLSVPs as another potential factor. The models link the earliest subduction to the MGI with implications forunderstanding the diverse tectonic regimes of rocky planets.
Climate extremes likely to drive land mammal extinction during next supercont...Sérgio Sacani
Mammals have dominated Earth for approximately 55 Myr thanks to their
adaptations and resilience to warming and cooling during the Cenozoic. All
life will eventually perish in a runaway greenhouse once absorbed solar
radiation exceeds the emission of thermal radiation in several billions of
years. However, conditions rendering the Earth naturally inhospitable to
mammals may develop sooner because of long-term processes linked to
plate tectonics (short-term perturbations are not considered here). In
~250 Myr, all continents will converge to form Earth’s next supercontinent,
Pangea Ultima. A natural consequence of the creation and decay of Pangea
Ultima will be extremes in pCO2 due to changes in volcanic rifting and
outgassing. Here we show that increased pCO2, solar energy (F⨀;
approximately +2.5% W m−2 greater than today) and continentality (larger
range in temperatures away from the ocean) lead to increasing warming
hostile to mammalian life. We assess their impact on mammalian
physiological limits (dry bulb, wet bulb and Humidex heat stress indicators)
as well as a planetary habitability index. Given mammals’ continued survival,
predicted background pCO2 levels of 410–816 ppm combined with increased
F⨀ will probably lead to a climate tipping point and their mass extinction.
The results also highlight how global landmass configuration, pCO2 and F⨀
play a critical role in planetary habitability.
Constraints on Neutrino Natal Kicks from Black-Hole Binary VFTS 243Sérgio Sacani
The recently reported observation of VFTS 243 is the first example of a massive black-hole binary
system with negligible binary interaction following black-hole formation. The black-hole mass (≈10M⊙)
and near-circular orbit (e ≈ 0.02) of VFTS 243 suggest that the progenitor star experienced complete
collapse, with energy-momentum being lost predominantly through neutrinos. VFTS 243 enables us to
constrain the natal kick and neutrino-emission asymmetry during black-hole formation. At 68% confidence
level, the natal kick velocity (mass decrement) is ≲10 km=s (≲1.0M⊙), with a full probability distribution
that peaks when ≈0.3M⊙ were ejected, presumably in neutrinos, and the black hole experienced a natal
kick of 4 km=s. The neutrino-emission asymmetry is ≲4%, with best fit values of ∼0–0.2%. Such a small
neutrino natal kick accompanying black-hole formation is in agreement with theoretical predictions.
Detectability of Solar Panels as a TechnosignatureSérgio Sacani
In this work, we assess the potential detectability of solar panels made of silicon on an Earth-like
exoplanet as a potential technosignature. Silicon-based photovoltaic cells have high reflectance in the
UV-VIS and in the near-IR, within the wavelength range of a space-based flagship mission concept
like the Habitable Worlds Observatory (HWO). Assuming that only solar energy is used to provide
the 2022 human energy needs with a land cover of ∼ 2.4%, and projecting the future energy demand
assuming various growth-rate scenarios, we assess the detectability with an 8 m HWO-like telescope.
Assuming the most favorable viewing orientation, and focusing on the strong absorption edge in the
ultraviolet-to-visible (0.34 − 0.52 µm), we find that several 100s of hours of observation time is needed
to reach a SNR of 5 for an Earth-like planet around a Sun-like star at 10pc, even with a solar panel
coverage of ∼ 23% land coverage of a future Earth. We discuss the necessity of concepts like Kardeshev
Type I/II civilizations and Dyson spheres, which would aim to harness vast amounts of energy. Even
with much larger populations than today, the total energy use of human civilization would be orders of
magnitude below the threshold for causing direct thermal heating or reaching the scale of a Kardashev
Type I civilization. Any extraterrrestrial civilization that likewise achieves sustainable population
levels may also find a limit on its need to expand, which suggests that a galaxy-spanning civilization
as imagined in the Fermi paradox may not exist.
Jet reorientation in central galaxies of clusters and groups: insights from V...Sérgio Sacani
Recent observations of galaxy clusters and groups with misalignments between their central AGN jets
and X-ray cavities, or with multiple misaligned cavities, have raised concerns about the jet – bubble
connection in cooling cores, and the processes responsible for jet realignment. To investigate the
frequency and causes of such misalignments, we construct a sample of 16 cool core galaxy clusters and
groups. Using VLBA radio data we measure the parsec-scale position angle of the jets, and compare
it with the position angle of the X-ray cavities detected in Chandra data. Using the overall sample
and selected subsets, we consistently find that there is a 30% – 38% chance to find a misalignment
larger than ∆Ψ = 45◦ when observing a cluster/group with a detected jet and at least one cavity. We
determine that projection may account for an apparently large ∆Ψ only in a fraction of objects (∼35%),
and given that gas dynamical disturbances (as sloshing) are found in both aligned and misaligned
systems, we exclude environmental perturbation as the main driver of cavity – jet misalignment.
Moreover, we find that large misalignments (up to ∼ 90◦
) are favored over smaller ones (45◦ ≤ ∆Ψ ≤
70◦
), and that the change in jet direction can occur on timescales between one and a few tens of Myr.
We conclude that misalignments are more likely related to actual reorientation of the jet axis, and we
discuss several engine-based mechanisms that may cause these dramatic changes.
The solar dynamo begins near the surfaceSérgio Sacani
The magnetic dynamo cycle of the Sun features a distinct pattern: a propagating
region of sunspot emergence appears around 30° latitude and vanishes near the
equator every 11 years (ref. 1). Moreover, longitudinal flows called torsional oscillations
closely shadow sunspot migration, undoubtedly sharing a common cause2. Contrary
to theories suggesting deep origins of these phenomena, helioseismology pinpoints
low-latitude torsional oscillations to the outer 5–10% of the Sun, the near-surface
shear layer3,4. Within this zone, inwardly increasing differential rotation coupled with
a poloidal magnetic field strongly implicates the magneto-rotational instability5,6,
prominent in accretion-disk theory and observed in laboratory experiments7.
Together, these two facts prompt the general question: whether the solar dynamo is
possibly a near-surface instability. Here we report strong affirmative evidence in stark
contrast to traditional models8 focusing on the deeper tachocline. Simple analytic
estimates show that the near-surface magneto-rotational instability better explains
the spatiotemporal scales of the torsional oscillations and inferred subsurface
magnetic field amplitudes9. State-of-the-art numerical simulations corroborate these
estimates and reproduce hemispherical magnetic current helicity laws10. The dynamo
resulting from a well-understood near-surface phenomenon improves prospects
for accurate predictions of full magnetic cycles and space weather, affecting the
electromagnetic infrastructure of Earth.
Extensive Pollution of Uranus and Neptune’s Atmospheres by Upsweep of Icy Mat...Sérgio Sacani
In the Nice model of solar system formation, Uranus and Neptune undergo an orbital upheaval,
sweeping through a planetesimal disk. The region of the disk from which material is accreted by
the ice giants during this phase of their evolution has not previously been identified. We perform
direct N-body orbital simulations of the four giant planets to determine the amount and origin of solid
accretion during this orbital upheaval. We find that the ice giants undergo an extreme bombardment
event, with collision rates as much as ∼3 per hour assuming km-sized planetesimals, increasing the
total planet mass by up to ∼0.35%. In all cases, the initially outermost ice giant experiences the
largest total enhancement. We determine that for some plausible planetesimal properties, the resulting
atmospheric enrichment could potentially produce sufficient latent heat to alter the planetary cooling
timescale according to existing models. Our findings suggest that substantial accretion during this
phase of planetary evolution may have been sufficient to impact the atmospheric composition and
thermal evolution of the ice giants, motivating future work on the fate of deposited solid material.
Emergent ribozyme behaviors in oxychlorine brines indicate a unique niche for...Sérgio Sacani
Mars is a particularly attractive candidate among known astronomical objects
to potentially host life. Results from space exploration missions have provided
insights into Martian geochemistry that indicate oxychlorine species, particularly perchlorate, are ubiquitous features of the Martian geochemical landscape. Perchlorate presents potential obstacles for known forms of life due to
its toxicity. However, it can also provide potential benefits, such as producing
brines by deliquescence, like those thought to exist on present-day Mars. Here
we show perchlorate brines support folding and catalysis of functional RNAs,
while inactivating representative protein enzymes. Additionally, we show
perchlorate and other oxychlorine species enable ribozyme functions,
including homeostasis-like regulatory behavior and ribozyme-catalyzed
chlorination of organic molecules. We suggest nucleic acids are uniquely wellsuited to hypersaline Martian environments. Furthermore, Martian near- or
subsurface oxychlorine brines, and brines found in potential lifeforms, could
provide a unique niche for biomolecular evolution.
Continuum emission from within the plunging region of black hole discsSérgio Sacani
The thermal continuum emission observed from accreting black holes across X-ray bands has the potential to be leveraged as a
powerful probe of the mass and spin of the central black hole. The vast majority of existing ‘continuum fitting’ models neglect
emission sourced at and within the innermost stable circular orbit (ISCO) of the black hole. Numerical simulations, however,
find non-zero emission sourced from these regions. In this work, we extend existing techniques by including the emission
sourced from within the plunging region, utilizing new analytical models that reproduce the properties of numerical accretion
simulations. We show that in general the neglected intra-ISCO emission produces a hot-and-small quasi-blackbody component,
but can also produce a weak power-law tail for more extreme parameter regions. A similar hot-and-small blackbody component
has been added in by hand in an ad hoc manner to previous analyses of X-ray binary spectra. We show that the X-ray spectrum
of MAXI J1820+070 in a soft-state outburst is extremely well described by a full Kerr black hole disc, while conventional
models that neglect intra-ISCO emission are unable to reproduce the data. We believe this represents the first robust detection of
intra-ISCO emission in the literature, and allows additional constraints to be placed on the MAXI J1820 + 070 black hole spin
which must be low a• < 0.5 to allow a detectable intra-ISCO region. Emission from within the ISCO is the dominant emission
component in the MAXI J1820 + 070 spectrum between 6 and 10 keV, highlighting the necessity of including this region. Our
continuum fitting model is made publicly available.
WASP-69b’s Escaping Envelope Is Confined to a Tail Extending at Least 7 RpSérgio Sacani
Studying the escaping atmospheres of highly irradiated exoplanets is critical for understanding the physical
mechanisms that shape the demographics of close-in planets. A number of planetary outflows have been observed
as excess H/He absorption during/after transit. Such an outflow has been observed for WASP-69b by multiple
groups that disagree on the geometry and velocity structure of the outflow. Here, we report the detection of this
planet’s outflow using Keck/NIRSPEC for the first time. We observed the outflow 1.28 hr after egress until the
target set, demonstrating the outflow extends at least 5.8 × 105 km or 7.5 Rp This detection is significantly longer
than previous observations, which report an outflow extending ∼2.2 planet radii just 1 yr prior. The outflow is
blueshifted by −23 km s−1 in the planetary rest frame. We estimate a current mass-loss rate of 1 M⊕ Gyr−1
. Our
observations are most consistent with an outflow that is strongly sculpted by ram pressure from the stellar wind.
However, potential variability in the outflow could be due to time-varying interactions with the stellar wind or
differences in instrumental precision.
X-rays from a Central “Exhaust Vent” of the Galactic Center ChimneySérgio Sacani
Using deep archival observations from the Chandra X-ray Observatory, we present an analysis of
linear X-ray-emitting features located within the southern portion of the Galactic center chimney,
and oriented orthogonal to the Galactic plane, centered at coordinates l = 0.08◦
, b = −1.42◦
. The
surface brightness and hardness ratio patterns are suggestive of a cylindrical morphology which may
have been produced by a plasma outflow channel extending from the Galactic center. Our fits of the
feature’s spectra favor a complex two-component model consisting of thermal and recombining plasma
components, possibly a sign of shock compression or heating of the interstellar medium by outflowing
material. Assuming a recombining plasma scenario, we further estimate the cooling timescale of this
plasma to be on the order of a few hundred to thousands of years, leading us to speculate that a
sequence of accretion events onto the Galactic Black Hole may be a plausible quasi-continuous energy
source to sustain the observed morphology
Efficient spin-up of Earth System Models usingsequence accelerationSérgio Sacani
Marine and terrestrial biogeochemical models are key components of the Earth System Models (ESMs) used toproject future environmental changes. However, their slow adjustment time also hinders effective use of ESMsbecause of the enormous computational resources required to integrate them to a pre-industrial equilibrium. Here,a solution to this "spin-up" problem based on "sequence acceleration", is shown to accelerate equilibration of state-of-the-art marine biogeochemical models by over an order of magnitude. The technique can be applied in a "blackbox" fashion to existing models. Even under the challenging spin-up protocols used for Intergovernmental Panelon Climate Change (IPCC) simulations, this algorithm is 5 times faster. Preliminary results suggest that terrestrialmodels can be similarly accelerated, enabling a quantification of major parametric uncertainties in ESMs, improvedestimates of metrics such as climate sensitivity, and higher model resolution than currently feasible.
Seminar of U.V. Spectroscopy by SAMIR PANDASAMIR PANDA
Spectroscopy is a branch of science dealing the study of interaction of electromagnetic radiation with matter.
Ultraviolet-visible spectroscopy refers to absorption spectroscopy or reflect spectroscopy in the UV-VIS spectral region.
Ultraviolet-visible spectroscopy is an analytical method that can measure the amount of light received by the analyte.
This pdf is about the Schizophrenia.
For more details visit on YouTube; @SELF-EXPLANATORY;
https://www.youtube.com/channel/UCAiarMZDNhe1A3Rnpr_WkzA/videos
Thanks...!
Slide 1: Title Slide
Extrachromosomal Inheritance
Slide 2: Introduction to Extrachromosomal Inheritance
Definition: Extrachromosomal inheritance refers to the transmission of genetic material that is not found within the nucleus.
Key Components: Involves genes located in mitochondria, chloroplasts, and plasmids.
Slide 3: Mitochondrial Inheritance
Mitochondria: Organelles responsible for energy production.
Mitochondrial DNA (mtDNA): Circular DNA molecule found in mitochondria.
Inheritance Pattern: Maternally inherited, meaning it is passed from mothers to all their offspring.
Diseases: Examples include Leber’s hereditary optic neuropathy (LHON) and mitochondrial myopathy.
Slide 4: Chloroplast Inheritance
Chloroplasts: Organelles responsible for photosynthesis in plants.
Chloroplast DNA (cpDNA): Circular DNA molecule found in chloroplasts.
Inheritance Pattern: Often maternally inherited in most plants, but can vary in some species.
Examples: Variegation in plants, where leaf color patterns are determined by chloroplast DNA.
Slide 5: Plasmid Inheritance
Plasmids: Small, circular DNA molecules found in bacteria and some eukaryotes.
Features: Can carry antibiotic resistance genes and can be transferred between cells through processes like conjugation.
Significance: Important in biotechnology for gene cloning and genetic engineering.
Slide 6: Mechanisms of Extrachromosomal Inheritance
Non-Mendelian Patterns: Do not follow Mendel’s laws of inheritance.
Cytoplasmic Segregation: During cell division, organelles like mitochondria and chloroplasts are randomly distributed to daughter cells.
Heteroplasmy: Presence of more than one type of organellar genome within a cell, leading to variation in expression.
Slide 7: Examples of Extrachromosomal Inheritance
Four O’clock Plant (Mirabilis jalapa): Shows variegated leaves due to different cpDNA in leaf cells.
Petite Mutants in Yeast: Result from mutations in mitochondrial DNA affecting respiration.
Slide 8: Importance of Extrachromosomal Inheritance
Evolution: Provides insight into the evolution of eukaryotic cells.
Medicine: Understanding mitochondrial inheritance helps in diagnosing and treating mitochondrial diseases.
Agriculture: Chloroplast inheritance can be used in plant breeding and genetic modification.
Slide 9: Recent Research and Advances
Gene Editing: Techniques like CRISPR-Cas9 are being used to edit mitochondrial and chloroplast DNA.
Therapies: Development of mitochondrial replacement therapy (MRT) for preventing mitochondrial diseases.
Slide 10: Conclusion
Summary: Extrachromosomal inheritance involves the transmission of genetic material outside the nucleus and plays a crucial role in genetics, medicine, and biotechnology.
Future Directions: Continued research and technological advancements hold promise for new treatments and applications.
Slide 11: Questions and Discussion
Invite Audience: Open the floor for any questions or further discussion on the topic.
(May 29th, 2024) Advancements in Intravital Microscopy- Insights for Preclini...Scintica Instrumentation
Intravital microscopy (IVM) is a powerful tool utilized to study cellular behavior over time and space in vivo. Much of our understanding of cell biology has been accomplished using various in vitro and ex vivo methods; however, these studies do not necessarily reflect the natural dynamics of biological processes. Unlike traditional cell culture or fixed tissue imaging, IVM allows for the ultra-fast high-resolution imaging of cellular processes over time and space and were studied in its natural environment. Real-time visualization of biological processes in the context of an intact organism helps maintain physiological relevance and provide insights into the progression of disease, response to treatments or developmental processes.
In this webinar we give an overview of advanced applications of the IVM system in preclinical research. IVIM technology is a provider of all-in-one intravital microscopy systems and solutions optimized for in vivo imaging of live animal models at sub-micron resolution. The system’s unique features and user-friendly software enables researchers to probe fast dynamic biological processes such as immune cell tracking, cell-cell interaction as well as vascularization and tumor metastasis with exceptional detail. This webinar will also give an overview of IVM being utilized in drug development, offering a view into the intricate interaction between drugs/nanoparticles and tissues in vivo and allows for the evaluation of therapeutic intervention in a variety of tissues and organs. This interdisciplinary collaboration continues to drive the advancements of novel therapeutic strategies.
The increased availability of biomedical data, particularly in the public domain, offers the opportunity to better understand human health and to develop effective therapeutics for a wide range of unmet medical needs. However, data scientists remain stymied by the fact that data remain hard to find and to productively reuse because data and their metadata i) are wholly inaccessible, ii) are in non-standard or incompatible representations, iii) do not conform to community standards, and iv) have unclear or highly restricted terms and conditions that preclude legitimate reuse. These limitations require a rethink on data can be made machine and AI-ready - the key motivation behind the FAIR Guiding Principles. Concurrently, while recent efforts have explored the use of deep learning to fuse disparate data into predictive models for a wide range of biomedical applications, these models often fail even when the correct answer is already known, and fail to explain individual predictions in terms that data scientists can appreciate. These limitations suggest that new methods to produce practical artificial intelligence are still needed.
In this talk, I will discuss our work in (1) building an integrative knowledge infrastructure to prepare FAIR and "AI-ready" data and services along with (2) neurosymbolic AI methods to improve the quality of predictions and to generate plausible explanations. Attention is given to standards, platforms, and methods to wrangle knowledge into simple, but effective semantic and latent representations, and to make these available into standards-compliant and discoverable interfaces that can be used in model building, validation, and explanation. Our work, and those of others in the field, creates a baseline for building trustworthy and easy to deploy AI models in biomedicine.
Bio
Dr. Michel Dumontier is the Distinguished Professor of Data Science at Maastricht University, founder and executive director of the Institute of Data Science, and co-founder of the FAIR (Findable, Accessible, Interoperable and Reusable) data principles. His research explores socio-technological approaches for responsible discovery science, which includes collaborative multi-modal knowledge graphs, privacy-preserving distributed data mining, and AI methods for drug discovery and personalized medicine. His work is supported through the Dutch National Research Agenda, the Netherlands Organisation for Scientific Research, Horizon Europe, the European Open Science Cloud, the US National Institutes of Health, and a Marie-Curie Innovative Training Network. He is the editor-in-chief for the journal Data Science and is internationally recognized for his contributions in bioinformatics, biomedical informatics, and semantic technologies including ontologies and linked data.
TEMPORAL EVOLUTION OF THE HIGH-ENERGY IRRADIATION AND WATER CONTENT OF TRAPPIST-1 EXOPLANETS.
1. Draft version July 31, 2017
Preprint typeset using LATEX style emulateapj v. 01/23/15
TEMPORAL EVOLUTION OF THE HIGH-ENERGY IRRADIATION AND WATER CONTENT OF
TRAPPIST-1 EXOPLANETS.
V. Bourrier1
, J. de Wit2
, E. Bolmont3
, V. Stamenkovi´c4,5
, P.J. Wheatley6
, A.J Burgasser7
, L. Delrez8
,
B.-O. Demory9
, D. Ehrenreich1
, M. Gillon10
, E. Jehin10
, J. Leconte11
, S.M. Lederer12
, N. Lewis13
,
A.H.M.J. Triaud14
, V. Van Grootel10
(Dated:)
Draft version July 31, 2017
ABSTRACT
The ultracool dwarf star TRAPPIST-1 hosts seven Earth-size transiting planets, some of which could
harbour liquid water on their surfaces. UV observations are essential to measure their high-energy
irradiation, and to search for photodissociated water escaping from their putative atmospheres. Our
new observations of TRAPPIST-1 Ly-α line during the transit of TRAPPIST-1c show an evolution of
the star emission over three months, preventing us from assessing the presence of an extended hydrogen
exosphere. Based on the current knowledge of the stellar irradiation, we investigated the likely history
of water loss in the system. Planets b to d might still be in a runaway phase, and planets within the
orbit of TRAPPIST-1g could have lost more than 20 Earth oceans after 8 Gyr of hydrodynamic escape.
However, TRAPPIST-1e to h might have lost less than 3 Earth oceans if hydrodynamic escape stopped
once they entered the habitable zone. We caution that these estimates remain limited by the large
uncertainty on the planet masses. They likely represent upper limits on the actual water loss because
our assumptions maximize the XUV-driven escape, while photodissociation in the upper atmospheres
should be the limiting process. Late-stage outgassing could also have contributed significant amounts
of water for the outer, more massive planets after they entered the habitable zone. While our results
suggest that the outer planets are the best candidates to search for water with the JWST, they also
highlight the need for theoretical studies and complementary observations in all wavelength domains
to determine the nature of the TRAPPIST-1 planets, and their potential habitability.
Keywords: planetary systems - Stars: individual: TRAPPIST-1
1. INTRODUCTION
The TRAPPIST-1 system has been found to host an
unprecedented seven Earth-sized planets (Gillon et al.
2016, Gillon et al. 2017). All seven of the TRAPPIST-1
planets were detected using the transit method (Winn
2010), which allows for the direct determination of
1 Observatoire de l’Universit´e de Gen`eve, 51 chemin des Mail-
lettes, 1290 Sauverny, Switzerland
2 Department of Earth, Atmospheric and Planetary Sciences,
Massachusetts Institute of Technology, 77 Massachusetts Av-
enue, Cambridge, MA 02139, USA
3 Laboratoire AIM Paris-Saclay, CEA/DRF - CNRS - Univ.
Paris Diderot - IRFU/SAp, Centre de Saclay, F- 91191 Gif-sur-
Yvette Cedex, France
4 Division of Geological and Planetary Sciences, California In-
stitute of Technology, Pasadena, CA 91125 USA
5 Jet Propulsion Laboratory, California Institute of Technol-
ogy, Pasadena, CA 91109 USA
6 Department of Physics, University of Warwick, Coventry
CV4 7AL, UK
7 Center for Astrophysics and Space Science, University of Cal-
ifornia San Diego, La Jolla, CA 92093, USA
8 Cavendish Laboratory, J J Thomson Avenue, Cambridge,
CB3 0HE, UK
9 University of Bern, Center for Space and Habitability, Si-
dlerstrasse 5, CH-3012, Bern, Switzerland
10 Institut dAstrophysique et de G´eophysique, Universit´e de
Li`ege, All´ee du 6 Aout 19C, 4000 Li`ege, Belgium
11 Laboratoire dAstrophysique de Bordeaux, Univ. Bordeaux,
CNRS, B18N, all´ee Geoffroy Saint-Hilaire, 33615 Pessac, France
12 NASA Johnson Space Center, 2101 NASA Parkway, Hous-
ton, Texas, 77058, USA
13 Space Telescope Science Institute, 3700 San Martin Drive,
Baltimore, Maryland 21218, USA
14 Institute of Astronomy, Madingley Road, Cambridge CB3
0HA, UK
their radii (Gillon et al. 2017, Table 1). Masses for the
TRAPPIST-1 planets (Gillon et al. 2017, Table 1) were
derived through transit-timing variations (TTV, Holman
& Murray 2005). The seventh planet’s properties were
recently refined by Luger et al. (2017), who showed that
three-body resonances link every planet of this complex
system. The combined mass and radius measurements
for the TRAPPIST-1 planets are consistent with rocky
water-enriched bulk compositions, with TRAPPIST-1
f having a density low enough to harbor up to 50% of
water in its mass. Three of the TRAPPIST-1 planets
(e to g) orbit within the habitable zone (HZ) (e.g.,
Kopparapu 2013), where water on a planet’s surface
is more likely to be in a liquid state. The planets in
the TRAPPIST-1 system present unique opportunity
thus far for single-system comparative studies aimed at
understanding the formation and evolution of terrestrial
exoplanet atmospheres.
The atmospheres of terrestrial exoplanets are ex-
pected to be diverse and shaped by a number of physical
processes (e.g., Leconte et al. 2015). Observationally
probing the TRAPPIST-1 planets over a broad wave-
length range from the ultraviolet (UV) to the infrared
(IR) provides insights into their current state and the
dominant physical processes shaping their atmospheres.
Because the TRAPPIST-1 planets transit their host stars
as seen from Earth, their atmospheres can be probed
via transmission spectroscopy (e.g. Seager & Sasselov
2000; Kaltenegger & Traub 2009). The atmospheres of
TRAPPIST-1b and c were probed at IR wavelengths by
2. 2 V. Bourrier et al.
Table 1
Characteristics of the TRAPPIST-1 exoplanets. Note that the mass of planet h could not be determined with TTV, we therefore
computed the mass range for two extreme compositions: 100% ice and 100% iron. We chose to base our analysis on the masses derived by
Gillon et al. (2017) rather than those of Wang et al. (2017) and Quarles et al. (2017), because these latter works were still under
reviewing at the time of submission of this paper.
Planets b c d e f g h
Mp(M⊕) 0.85±0.72 1.38±0.61 0.41±0.27 0.62±0.58 0.68±0.18 1.34±0.88 0.06 – 0.86
Rp(R⊕) 1.086 1.056 0.772 0.918 1.045 1.127 0.752
ρp(ρ⊕) 0.66±0.56 1.17±0.53 0.89±0.60 0.80±0.76 0.60±0.17 0.94±0.63 0.14 – 2.02
ap (au) 0.01111 0.01521 0.02144 0.02817 0.0371 0.0451 0.059
de Wit et al. (2016) using the Hubble Space Telescope
(HST), which found the atmospheres of these planets to
be inconsistent with clear, hydrogen-rich “primordial”
atmospheres. However, a number of plausible scenarios
still exist for the atmospheres of TRAPPIST-1b and c,
including water-rich and aerosol-laden atmospheres. A
robust interpretation of current and future observations
of TRAPPIST-1 at IR wavelengths will require a better
understanding of atmospheric chemistry and escape
processes shaping these planets, which can be provided
by observations at UV wavelengths.
Ultraviolet transit spectroscopy is a powerful way
to search for signatures of atmospheric escape from
exoplanets. Extended atmospheres of neutral hydro-
gen have been detected through observations of the
stellar Lyman-α line (Ly-α, at 1215.67 ˚A) during the
transit of Jupiter-mass planets (Vidal-Madjar et al.
2003; Ehrenreich et al. 2012; Lecavelier des Etangs
et al. 2010, 2012) and Neptune-mass planets (Kulow
et al. 2014, Ehrenreich et al. 2015). Because of their
spatial extent and kinetic broadening (e.g., Ekenb¨ack
et al. 2010, Bourrier & Lecavelier des Etangs 2013),
exospheres transit longer than the lower atmospheric
layers probed at optical/infrared wavelengths, and yield
deep transit signatures over a large spectral range.
The case of the warm Neptune GJ 436b, in particular,
revealed that small planets around cool M dwarfs can
support giant exospheres, yielding up to half-eclipses of
the star at Ly-α (Bourrier et al. 2015, Bourrier et al.
2016b). UV observations of Earth-size planets in a
system like TRAPPIST-1 thus offer great perspectives
for constraining their atmospheric properties. The
faint Ly-α line of this cold M8 star was detected by
Bourrier et al. 2017 (hereafter B17) using the Hubble
Space Telescope (HST), with enough light to perform
transit spectroscopy. Hints of variations were identified
at the time of the transits of inner planets b and c,
which could either indicate extended atmospheres of
neutral hydrogen or intrinsic stellar variability. The
first objective of the present study was to reobserve
the TRAPPIST-1 system in the Ly-α line during a
TRAPPIST-1c transit, to search for signatures of an
extended atmosphere, and to improve our understanding
of the high-energy stellar emission.
Despite recent efforts (France et al. 2013, France
et al. 2016) our understanding of the atmospheres of
exoplanets around M dwarf stars remains limited by the
lack of observational and theoretical knowledge about
the UV and X-rays spectra of these cool stars. Yet
these stars currently offer the best opportunity to detect
and characterize Earth-size planets in the habitable
zone (HZ). Measuring their UV irradiation is crucial
because it impacts the stability and erosion of planetary
atmospheres (e.g., Lammer et al. 2003, Koskinen et al.
2007, Bolmont et al. 2017), controls photochemical
reactions in the outer atmosphere (Miguel et al. 2015),
and can further influence the developement and survival
of life on a planet surface (see, e.g., O’Malley-James &
Kaltenegger 2017, Ranjan et al. 2017 for TRAPPIST-1).
The high present-day X-rays to ultraviolet (XUV) emis-
sion from TRAPPIST-1 (Wheatley et al. 2017) and the
fact that M dwarfs can remain active for several billon
years suggest that the atmospheres of the TRAPPIST-1
planets could have been subjected to significant mass
loss over the course of their history. Water, in particular,
could have been lost through photolysis and atmospheric
escape, a process which has been previously studied by
Bolmont et al. (2017) for TRAPPIST-1b, c, and d. At
the time of their study, only those three planets were
known, and the XUV emission of the star was not yet
observationally-constrained.
Our second objective in this paper is to revise the
calculations of water-loss for all TRAPPIST-1 planets,
benefiting from our improved knowledge of the system
architecture (Gillon et al. 2017) and of the stellar XUV
irradiation (Wheatley et al. 2017, B17, and new Ly-α
measurements presented in this paper). The planet prop-
erties used in our analysis are given in Table 1. HST
observations of TRAPPIST-1 are presented in Sect. 2,
and used in Sect. 3 to study the high-energy stellar emis-
sion and its temporal evolution. Sect. 4 describes how the
stellar irradiation influences the water loss from the plan-
etary atmospheres, while Sect. 5 addresses the limiting
effect of hydrogen production. We discuss the evolution
of TRAPPIST-1 exoplanet atmospheres in Sect. 6.
2. OBSERVATIONS AND DATA REDUCTION
We observed the H i Ly-α line (1215.6702 ˚A) of
TRAPPIST-1 at four independent epochs in 2016,
using the Space Telescope Imaging Spectrograph (STIS)
instrument on board the HST. The log of these obser-
vations is given in Table 2. The star was observed at
three epochs during Mid-Cycle Program 14493 (PI: V.
Bourrier). Two consecutive HST orbits were obtained
on 26 September (Visit 1), at a time when none of the
seven planets were transiting (all planets were between
135◦
and 330◦
past their last respective transits). A
single HST orbit was obtained during the transit of
TRAPPIST-1b on 30 September (Visit 2), and another
one about 1.7 h after the transit of TRAPPIST-1c on
23 November (Visit 3). No other planets were close
3. Irradiation and water loss of TRAPPIST-1 exoplanets 3
−0.06 −0.03 0.00 0.03 0.06
Distance (au)
−0.06
−0.03
0.00
0.03
0.06
Distance(au)
bcdefgh
−10 −5 0 5 10
Distance (R*
)
−2
0
2
Dist.(R*
)
Figure 1. Orbital positions of the TRAPPIST-1 planets at the
time of the HST observations in Visit 4. Each rectangle corre-
sponds to the space covered by a planet during one of the HST
orbits. Upper panel: View from the above of the planetary sys-
tem. Planets are moving counterclockwise. The dashed black line
indicates the line-of-sight (LOS) toward Earth. Star and orbital
trajectory have the correct relative scale. Lower panel: View from
Earth.
to transiting during Visits 2 and 3. Results of this
reconnaissance program were published in B17. We
obtained five new orbits on December 25, 2016 during
the GO/DD Program 14900 (PI: J. de Wit). Visit 4 was
scheduled to include a TRAPPIST-1c transit, to search
for the signature of a hydrogen exosphere around the
planet. The configuration of the planetary system at
the time of Visit 4 is shown in Fig. 1. Note that because
of occultations by the Earth and the time required to
acquire the target star with the HST, about a third of
an HST orbit could be spent observing TRAPPIST-1 at
Lyman-α.
Table 2
Log of TRAPPIST-1 Ly-α observations in 2016.
Visit Date Time (UT)
Start End
1 Sept-26 02:51:50 04:59:45
2 Sept-30 22:55:05 23:27:38
3 Nov-23 20:56:10 21:28:35
4 Dec-25 03:17:58 10:10:17
All four visits made use of STIS Far Ultraviolet
Multi-Anode Microchannel Array (FUV-MAMA) de-
tector, and the G140M grating at 1222 ˚A. Data were
reduced with the CALSTIS pipeline. In the region
of the Ly-α line the background is dominated by the
−200 −100 0 100 200
Velocity in star rest frame (km s−1
)
0.000
0.005
0.010
0.015
Countss−1
Figure 2. Raw spectra of the stellar Ly-α line in Visit 4 (solid
line histogram), after correction from the geocoronal emission line
(superimposed as a dashed line). Colors correspond to HST orbits
at consecutive orbital phases (increasing from black, blue, green,
orange, red). Gray vertical lines indicate the range excluded from
our analysis, where the airglow is so strong that its correction re-
sults in spurious flux values.
Earth’s geocoronal airglow emission (Vidal-Madjar et al.
2003). The error bars in the final 1D spectra account for
the uncertainty in the airglow flux, but the correction
performed by the pipeline can yield spurious flux values
where the airglow is much stronger than the stellar line.
The position, amplitude, and width of the airglow line
profile varies in strength and position with the epoch
of observation (e.g. Bourrier et al. 2016a), and we thus
excluded from our analysis the contaminated ranges
[-3 ; 129] km s−1
(Visit 1), [-4 ; 102] km s−1
(Visit 2),
[-8 ; 110] km s−1
(Visit 3), and [-29 ; 116] km s−1
(Visit
4), defined in the star rest frame. Airglow is much
stronger in Visit 4 because TRAPPIST-1 was nearly
four months past opposition (see Fig. 2), and we found
that the stellar spectrum between -150 and -29 km s−1
depended on the areas of the 2D images used to build the
background profile. The background is extracted and
averaged automatically by the pipeline from two regions
above and below the spectrum. For the FUV-MAMA
D1 aperture used in Visit 4, the standard regions are 5
pixels wide and located ±30 pixels from the spectrum
along the cross-dispersion axis. We varied this distance
and found that individual airglow-corrected exposures
showed differences in the blue wing of the stellar Ly-α
line when the background was extracted from regions
farther than ∼25 pixels from the spectrum. We thus
limited the effect of airglow contamination by measuring
an accurate local background within extraction regions
that extend between 6 and 20 pixels from each side of
the spectrum.
Data in each orbit, obtained in time-tagged mode,
were divided into five shorter sub-exposures (varying
from 380 to 450 s depending on the duration of the
initial exposure). This allowed us to check for variations
at short time scales within a given HST orbit caused by
the telescope breathing (e.g., Bourrier et al. 2013). We
modeled the breathing effect using either a Fourier series
decomposition (Bourrier et al. 2016a) or a polynomial
function (e.g., Ehrenreich et al. 2012). The model was
fitted to the flux integrated over the entire Ly-α line,
excluding the range contaminated by airglow emission,
and using the Bayesian Information Criterion (BIC) as
4. 4 V. Bourrier et al.
Figure 3. Ly-α fluxes for all sub-exposures in Visit 4, integrated
over the entire line (excluding the airglow range) and phase-folded
on the HST orbital period. No variations caused by the telescope
breathing were detected, with no significant deviations from the
mean flux (black dashed line). Colors correspond to HST orbits
at consecutive orbital phases (increasing from black, blue, green,
orange, red).
a merit function (Crossfield et al. 2012). No variations
caused by the telescope breathing were detected in any
of the visits (see Fig. 3 for Visit 4), most likely because
it is dominated by the photon noise from the very faint
Ly-α line and because there are not enough HST orbits
to sample its variations properly in Visits 1 to 3.
3. ANALYSIS OF TRAPPIST-1 FUV OBSERVATIONS
3.1. Long-term evolution of the stellar Ly-α line
A high-quality reference spectrum for the intrinsic
stellar Ly-α line of TRAPPIST-1 was built by B17 as
the average of all spectra obtained in Visits 1, 2, and 3,
excluding the spectral ranges contaminated by airglow
emission or showing hints of flux variations. We first
compared the Ly-α line spectra obtained in each expo-
sure of Visit 4 with this reference spectrum, searching for
absolute flux variations over ranges covering more than
STIS spectral resolution (about two pixels). As can be
seen in Fig.4 the flux in the red wing of Visit 4 spectra
is systematically higher than or equal to the reference
spectrum, with a significant (>3σ) increase in orbits 2,
3, and 5. Similarly the reference spectrum shows very
little emission in the blue wing at velocities lower than
about -160 km s−1
, whereas the flux in Visit 4 spectra is
systematically higher than or equal to the reference in
this range, with a marginal (>2σ) increase in orbits 2,
3, and 4. Therefore it comes as a surprise that Visit 4
displays an overall lower flux in the blue wing between
about -120 and -55 km s−1
, with significant decreases in
orbits 2 and 5 compared to the reference spectrum.
To investigate the source of these differences we stud-
ied the evolution of the Ly-α line over the three months
span of our observations, averaging all spectra within
each visit, and integrating them in four complementary
spectral bands (Fig. 5). In agreement with the above
spectral analysis, the flux in the symmetric wing bands
(±[130 ; 250] km s−1
) did not vary significantly from
Visit 1 to Visit 3 (top panels in Fig. 5) but increased
noticeably in Visit 4. This variation likely traces an
increase in the emission of the intrinsic stellar Ly-α line
(Sect. 3.2). However, while we do not expect similar
Figure 4. Ly-α line spectra in Visit 4, overplotted with their
average over the visit (black spectrum), and with the reference
spectrum from B17 (grey spectrum). Spectra were shifted along
the vertical axis (dotted black lines indicate the null level in each
orbit). The dashed range is contaminated by airglow emission.
TRAPPIST-1 Ly-α line is so faint that in some pixels no photons
were detected over the duration of the exposure.
absolute flux levels in the observed wing bands because
of interstellar medium (ISM) absorption in the red wing
of the Ly-α line (see B17), it is surprising that the
relative flux increase in Visit 4 is much larger and more
significant in the red wing than in the blue wing. The
flux in the blue wing even shows a marginal decline at
lower velocities ([-130 ; -50] km s−1
) from Visit 1 to Visit
4 (third panel in Fig. 5), while the flux at velocities
closer to the Ly-α line core ([-50 ; -25] km s−1
) remained
at about the same flux level (bottom panel in Fig. 5).
This comparison suggests that the shape of the line
evolved between Visit 1 and Visit 4, with a change in the
spectral balance of the Ly-α line flux between the blue
and the red wings. The search for absorption signatures
possibly caused by the transit of TRAPPIST-1c in Visit
4 is made difficult by this evolution, since the spectra
from Visits 1-3 cannot be used as a reference for the
out-of-transit stellar line. We investigate this question
in more details in Sect. 3.3.
3.2. High-energy stellar emission
5. Irradiation and water loss of TRAPPIST-1 exoplanets 5
0 20 40 60 80 100
Time (BJD − 2457652)
0.0
0.2
0.4
0.6
0.8
Flux(10−15
ergs−1
cm−2
)
Band: 130 ; 250 km/s
0 20 40 60 80 100
Time (BJD − 2457652)
0.0
0.2
0.4
0.6
Flux(10−15
ergs−1
cm−2
)
Band: −250 ; −130 km/s
0 20 40 60 80 100
Time (BJD − 2457652)
0.4
0.6
0.8
1.0
1.2
1.4
Flux(10−15
ergs−1
cm−2
)
Band: −130 ; −50 km/s
0 20 40 60 80 100
Time (BJD − 2457652)
0.2
0.4
0.6
Flux(10−15
ergs−1
cm−2
)
Band: −50 ; −25 km/s
Figure 5. Evolution of the Ly-α flux over time, integrated in four
complementary bands (indicated in each panel). All spectra have
been interpolated over a common wavelength table before being
averaged in each visit. Each point thus corresponds to the mean
spectrum over a visit. The dashed line indicates the flux level in
Visit 1, measured outside of any planet transit.
To further study the evolution of the stellar Ly-α
line, we sought to reconstruct its intrinsic profile at the
time of Visit 4 using the same approach as in B17. We
assumed a Gaussian line profile, which was absorbed by
the ISM using the column density derived in B17. The
model was then convolved by the STIS line spread func-
tion (LSF), and compared with the average of all spectra
in Visit 4. We excluded the pixels beyond ±250 km s−1
from the fit, where the wings of the line become too faint.
We also excluded the core of the line fully absorbed
by the ISM and possibly biased by the airglow correction.
Contrary to the reconstruction performed in B17 on
Visit 1-3 reference spectrum, in Visit 4, we found that it
was not possible to fit the entire line profile well with
our theoretical Gaussian model. Trying out different
spectral ranges for the reconstruction, we found that a
good fit was obtained when excluding the band [-190 ;
-55] km s−1
, even in the range contaminated by the air-
glow (Fig. 6). This best-fit line profile for Visit 4 peaks
at about the same flux level as the reference spectrum
in Visit 1-3 but displays much broader wings, which is
consistent with the stability of the Ly-α line core and
the variability of its wings noted in Sect. 3.1. Assuming
this best-fit model is correct, it would suggest that both
wings of the Ly-α line have increased similarly from Visit
1-3 to Visit 4, but that the band [-190 ; -55] km s−1
is
re-absorbed by an unknown source in this epoch. Alter-
natively, the intrinsic Ly-α line of TRAPPIST-1 could
have become asymmetric in Visit 4. Both scenarios
would explain why the line profile observed in Visit 4
appears unbalanced between the blue and the red wing
(see Sect. 3.1 and Fig. 5). We further investigate this
question in Sect. 3.3.
The Lyman-α line arises from different regions of
the stellar atmosphere, ranging from the low-flux
wings of the line formed in the colder regions of the
lower chromosphere, to the core of the line, which is
emitted by the hot transition region between the upper
chromosphere of the star and its corona. M dwarfs
display a lower chromospheric emission than earlier-type
stars, but equivalent amounts of emission from the
transition region and the corona (see Youngblood et al.
2016 and references). This trend might be even more
pronounced for late-type M dwarfs like TRAPPIST-1,
since B17 suggested that this ultracool dwarf might have
a weak chromosphere compared to its transition region
and corona, based on its Lyman-α and X-ray emission
(Wheatley et al. 2017) and the shape of its Ly-α line.
Interestingly though, the broader wings of TRAPPIST-1
Ly-α line in Visit 4 might trace an increase in the
temperature and emission of the stellar chromosphere.
In addition to the Ly-α line, the spectral range of
the STIS/G140M grating covers the Si iii (1206.5 ˚A)
and O v (1218.3 ˚A) transitions, and the N v doublet
(1242.8 ˚A and 1238.8 ˚A). We averaged our nine STIS
spectra of TRAPPIST-1 to search for these stellar
emission lines, and detected the N v doublet (Fig. 7).
The two lines of the doublet were averaged and fitted
with a Gaussian profile. Assuming that the width of the
line is controlled by thermal broadening, we obtained a
best-fit temperature on the order of 3×105
K, which is
close to the peak emissivity of the N v lines at 2×105
K.
We further derived a total flux in the doublet of about
7.3×10−17
erg s−1
cm−2
. This line strength is consistent
with the fits to the X-ray spectrum of TRAPPIST-1 by
Wheatley et al. 2017, which predict N v line strengths of
1×10−17
and 100×10−17
erg s−1
cm−2
for two different
models designed to span the possible range of EUV lu-
minosities (the APEC and cemekl models respectively).
The dispersion is larger in the regions of the other stellar
lines and there is no clear evidence for their detection.
More observations will be required to characterize the
chromospheric and coronal emission from TRAPPIST-1.
3.3. The mysterious shape of TRAPPIST-1 Ly-α line
B17 reported a hint of absorption in the blue wing of
the Ly-α line in Visit 3, possibly caused by a hydrogen
exosphere trailing TRAPPIST-1c. The long-term
evolution of the intrinsic Ly-α line prevents us from
comparing the different visits from one another, and
we thus took the average of all spectra in Visit 4 as a
reference to search for the presence of an exosphere in
this epoch. We highlight the long-term variability in
Fig. 8, where we plotted the flux integrated in the same
spectral bands as in Fig. 5 but phase-folded over the
TRAPPIST-1c orbital period. The spectrum measured
in Visit 3 shows a lower flux level at high velocities in the
wing bands compared to the average flux in Visit 4 but
6. 6 V. Bourrier et al.
Figure 6. Ly-α line profiles of TRAPPIST-1. Solid-line profiles
correspond to our best estimates for the theoretical intrinsic Ly-
α line in Visit 1-3 (blue) and in Visit 4 (black). They yield the
dashed-line profiles after ISM absorption and convolution by STIS
LSF. ISM absorption profile in the range 0-1 has been scaled to
the vertical axis range and plotted as a dotted black line. The
dashed-line profile in Visit 4 was fitted to the observations (red
histogram, equal to the average of all spectra in Visit 4) outside
of the hatched regions, and excluding the variable range between
-187 and -55 km s−1 (highlighted in orange). Note that the model
fits the observations well, even in the range contaminated by the
airglow (except where it is strongest between 0 and 50 km s−1).
Figure 7. Average spectrum of TRAPPPIST-1 in the star rest
frame in the ranges of the Si iii line (top panel), the O v line (middle
panel), and the N v doublet (bottom panel). Pixels are binned by
two for the sake of clarity. The blue dashed lines indicate the rest
wavelength of the stellar lines. The green line is the mean flux in
the range (excluding the region blueward of the O v line, since it is
dominated by the red wing of the Ly-α line). In the bottom panel,
the lines of the N v doublet have been averaged in velocity space
and fitted with a Gaussian model. Each N v line is indicated by
a dotted blue line at the velocity of its transition relative to the
other line of the doublet.
similar flux levels in other parts of the line, consistent
with the changes in the intrinsic line shape discussed
in Sect. 3.1. No significant deviations to the average
spectrum were found in Visit 4, and in particular no
variations that would be consistent with the transit
of an extended exosphere surrounding TRAPPIST-1c.
More observations will be required to assess the possible
short-term variability in the Ly-α line and to search for
residual absorption signatures.
If the Ly-α line model derived in Sect. 3.2 corresponds
to the actual intrinsic line of the star in Visit 4, what is
the origin of the much lower flux observed in the band
[-190 ; -70] km s−1
(Fig. 6) ? Despite our careful extrac-
tion of the stellar spectrum (Sect. 2), it is possible that
the stronger airglow in this epoch was overcorrected at
some wavelengths. However, the airglow becomes neg-
ligible beyond about -100 km s−1
, and therefore cannot
explain the lower flux observed at larger velocities. If
confirmed, this feature might imply that colder hydro-
gen gas is moving away from the star at high velocities
and is absorbing about half of the Ly-α flux in this veloc-
ity range. This absorption is unlikely to originate from
TRAPPIST-1c alone, as it occurs in all orbits of Visit 4
and displays no correlation with the planet transit. Ra-
diative braking is less efficient around TRAPPIST-1 than
around the M2.5 dwarf GJ 436 (Bourrier et al. 2015), be-
cause its radiation pressure is about three times lower
and thus more than five times lower than stellar grav-
ity (B17). This could lead to the formation of giant
hydrogen exospheres around the TRAPPIST-1 planets
even larger than the one surrounding the warm Neptune
GJ 436b (Ehrenreich et al. 2015), and possibly extending
both behind and ahead of the planets because of gravi-
tational shear (Bourrier et al. 2015). Furthermore, the
XUV spectrum of TRAPPIST-1 (Sect. 4.2) yields pho-
toionization lifetimes for neutral hydrogen atoms rang-
ing from ∼20 h at the orbit of TRAPPIST-1b to nearly
600 h at the orbit of TRAPPIST-1h (i.e., longer than
the planetary period). Because of the very low Ly-α
and UV emission from TRAPPIST-1, neutral hydrogen
exospheres could thus extend along the entire planetary
orbits, and could even cross the orbit of several planets.
This not only suggests that some planets could be ac-
creting the gas escaped from their companions, but also
that a large volume of the TRAPPIST-1 system could
be filled with neutral hydrogen gas, providing a possi-
ble explanation for the persistent absorption signature
in Visit 4. Given that the evaporating planets sustain-
ing this system-wide hydrogen cloud would be in differ-
ent relative positions at a given epoch, the structure of
the cloud and its absorption signature would be highly
variable over time, which could explain why it was not
detected in Visit 1. We note, though, that the hydro-
gen cloud would still have to be accelerated to very high
velocities away from the star (possibly through charge-
exchange with the stellar wind, Holmstr¨om et al. 2008,
Ekenb¨ack et al. 2010, Bourrier et al. 2016b) to explain
the velocity range of the measured absorption.
Alternatively, this variation could have a stellar
origin. This is also an intriguing possibility, because
the Ly-α line of TRAPPIST-1 was well approximated
with a Gaussian profile in previous visits (B17), and the
Ly-α line profiles of later-type M dwarfs do not show
7. Irradiation and water loss of TRAPPIST-1 exoplanets 7
−4 −2 0 2 4
Time (h)
0.5
1.0
Flux(10−15
ergs−1
cm−2
)
Band: 130 ; 250 km/s
−4 −2 0 2 4
Time (h)
0.0
0.5
1.0
Flux(10−15
ergs−1
cm−2
)
Band: −250 ; −130 km/s
−4 −2 0 2 4
Time (h)
0.0
0.5
1.0
1.5
Flux(10−15
ergs−1
cm−2
)
Band: −130 ; −50 km/s
−4 −2 0 2 4
Time (h)
0.2
0.4
0.6
0.8
Flux(10−15
ergs−1
cm−2
)
Band: −50 ; −25 km/s
Figure 8. Ly-α flux integrated in the same complementary bands
as in Fig. 5, and plotted as a function of time relative to the transit
of TRAPPIST-1c. Vertical dotted lines indicate the transit contact
times. Black points correspond to Visit 4, and the orange point for
Visit 3. The dashed line is the mean flux in Visit 4.
evidence for strong asymmetries (e.g., Bourrier et al.
2015, Youngblood et al. 2016). The intrinsic Ly-α line of
TRAPPIST-1 might have become asymmetric in Visit 4
because of variations in the up-flows and down-flows of
stellar hydrogen gas, or because of absorption by colder
hydrogen gas at high altitudes in the stellar atmosphere.
Filaments made of partially-ionized plasma are, for the
Sun, a hundred times cooler and denser than the coronal
material in which they are immersed, and can thus be
optically thick in the Ly-α line (e.g., Parenti 2014). The
large velocities of the putative absorber of TRAPPIST-1
Ly-α line might indicate that we witnessed the eruption
of a filament that was expelled by a destabilization of
the stellar magnetic field. Such eruptions can reach large
distances and velocities (between 100 to 1000 km s−1
for
the Sun, e.g. Schrijver et al. 2008). In any case, our
new observations of TRAPPIST-1 raise many questions
about the physical mechanisms behind the emission of
the Ly-α line in an ultracool dwarf.
Despite these unknowns, our best-fit Gaussian profile
can be used to estimate a conservative upper limit on
the total Ly-α irradiation of the planets at the epoch of
Visit 4 (Sect. 4.2). More observations of TRAPPIST-1
at Ly-α will be required to beat down the photon noise,
to assess the effects of stellar variability, and to reveal ab-
sorption signatures caused by the putative planets’ exo-
spheres. The long-term variability of TRAPPIST-1 Ly-α
line emphasizes the need for contemporaneous observa-
tions obtained outside and during the planet’s transits.
4. EVOLUTION OF THE PLANETS UNDER HIGH-ENERGY
IRRADIATION
Two types of spectral radiation are involved in the
escape of water from an exoplanet: far-UV (FUV,
100–200 nm) to photo-dissociate water molecules and
XUV (0.1–100 nm) to heat up the upper atmosphere
and allow for the escape of the photo-dissociation
products, hydrogen and oxygen (e.g., Vidal-Madjar
et al. 2003, Lammer et al. 2003). In this section, we
study the evolution of water loss from the TRAPPIST-1
planets, in particular during their runaway greenhouse
phase (see Barnes & Heller 2013; Luger & Barnes 2015
and Bolmont et al. 2017 for generic brown dwarfs and
M-dwarfs and Ribas et al. 2016 and Barnes et al. 2016
for the M-dwarf planet Proxima-b). The idea is that
once a planet reaches the HZ, its water can recombine
and condense. Thus the amount of water reaching the
upper layers of the atmosphere would be much lower
than the amount available during a runaway phase.
With a low mass of 0.0802 ± 0.0073 M , TRAPPIST-1
(stellar type M8) is just above the limit between brown
dwarfs and M-dwarfs and is expected to cool down for
about 1 Gyr before reaching the Main Sequence (MS).
During this initial phase all TRAPPIST-1 planets,
including those in the HZ today (planets e, f and g
according to Gillon et al. 2017), were hot enough for the
water potentially delivered during the formation process
to be injected in gaseous form into the atmosphere, and
lost more easily (Jura 2004, Selsis et al. 2007).
In a first step we estimated the duration of the run-
away greenhouse phases for the TRAPPIST-1 planets.
Figure 9 shows the present day orbital distances of
the seven planets, and the evolution of the HZ inner
limits for a TRAPPIST-1 analog. Using the mass
of TRAPPIST-1 (0.0802 M ) yielded an HZ inner
edge much closer-in to what is shown in Gillon et al.
(2017), because low-mass star evolution models tend to
underestimate the luminosity for active stars (Chabrier
et al. 2007) such as TRAPPIST-1 (Luger et al. 2017,
Vida et al. 2017). We therefore revised the stellar mass
for TRAPPIST-1 following the prescription of Chabrier
et al. (2007), by greatly reducing convection efficiency
in CLES stellar evolution models (Scuflaire et al. 2008).
We estimate a stellar mass of 0.091±0.005 M using
TRAPPIST-1’s luminosity (Filippazzo et al. 2015),
density and metallicity (Gillon et al. 2017) as inputs.
The error bars include uncertainties associated with
these input parameters, as well as on the initial helium
abundance. This stellar mass is fully consistent with
the most recent dynamical mass estimates based on
ultra cool binaries for TRAPPIST-1s spectral type
(Dupuy & Liu 2017), and with the larger radius derived
by Burgasser & Mamajek (2017). The inferred age
is greater than 2 Gyr (the star evolves too slowly to
constrain its age through stellar evolution models),
consistent with the 3-8 Gyr (Luger et al. 2017) and
7.6±2.2 Gyr (Burgasser & Mamajek 2017) age estimates
for TRAPPIST-1. The evolution of the HZ inner edge
was calculated for two different assumptions regarding
the rotation of the planets. The first one (Sp = 1.5 S⊕,
where Sp is the insolation received by the planet and S⊕
the solar insolation received by the Earth) corresponds
8. 8 V. Bourrier et al.
to a synchronized planet. This estimation comes from
Yang et al. (2013), which showed that a tidally locked
planet could sustain surface liquid water closer to the
star due to the protection of the substellar point by
water clouds. The second one (Sp = 0.84 S⊕) is the
classical limit, computed for a non-synchronous planet
(Kopparapu 2013). Note that the planet does not
require as much incident flux as the Earth to maintain
the same surface temperature because of the redness
of the star. For instance, the albedo of ice and snow
is significantly lower in the infrared (Joshi & Haberle
2012), which means that the temperature of a planet is
higher around TRAPPIST-1 than around a Solar-type
star for a given flux and therefore, the inner edge of the
HZ corresponds to a lower incoming flux. We estimated
the age at which the planets entered the shrinking HZ
(Table 3), considering that their migration stopped when
the gas disk dissipated (Luger et al. 2017, Tamayo et al.
2017). This age corresponds to the end of the runaway
greenhouse phase, and we found it lasted between a
few 10 Myr (for planet h) to a few 100 Myr (for planet
d, in the synchronized scenario). The HZ stabilized
at about 1 Gyr, earlier than the lower limit on the age
of TRAPPIST-1 given by Luger et al. (2017). This
suggests that planets d to h have already been subjected
to the strongest phases of their atmospheric erosion,
but that planets b and c might still be in their runaway
greenhouse phase if they were formed with enough water.
Sp = 1.5 S⨁
Sp = 0.84 S⨁
HZ inner edge
T1-b
T1-c
T1-d
T1-e
T1-f
T1-g
T1-h
Figure 9. Architecture of the TRAPPIST-1 system and evolu-
tion of the inner edge of the HZ for two different hypotheses: a
synchronized planet (Sp = 1.5 S⊕, see Yang et al. 2013) and a
non-synchronized planet (Sp = 0.84 S⊕, see Kopparapu 2013).
The thick blue line corresponds to HZ inner edges which were cal-
culated from evolutionary models for a 0.091 M dwarf (Sect. 4
and Van Grootel et al. (submitted)). The blue areas correspond
to the uncertainties on the HZ inner edge due to the uncertainty
of the mass of the star.
4.1. Water loss model
We calculated mass-loss rates from TRAPPIST-1 plan-
ets using an improved formalism based on the energy-
limited formula (e.g. Lecavelier des Etangs 2007, Selsis
et al. 2007, Luger & Barnes 2015):
˙Mtot
= (
RXUV
Rp
)2 3 FXUV(ap)
4 G ρp Ktide
, (1)
with FXUV(ap) the XUV irradiation. The heating effi-
ciency is the fraction of the incoming energy that is
transferred into gravitational energy through mass loss.
As in Bolmont et al. (2017) and Ribas et al. (2016), we
calculated using 1D radiation-hydrodynamic mass-loss
simulations based on Owen & Alvarez (2016). varies
with the incoming XUV radiation. For example, for to-
day’s estimated XUV flux (see next Section and Table
4) we obtain values of 0.064, 0.076, 0.089, 0.099, 0.107,
0.112 and 0.115, respectively for planets b to h. These
efficiencies are on the same order as the 10% assumed by
Wheatley et al. 2017 but larger than the 1% assumed by
Bourrier et al. (2017).
In the following sections, we consider a constant XUV
flux and an evolving XUV flux. For the latter as-
sumption, is computed accordingly. In the energy-
limited formula the parameter (RXUV
Rp
)2
accounts for the
increased cross-sectional area of planets to XUV radia-
tion, while Ktide accounts for the contribution of tidal
forces to the potential energy (Erkaev et al. 2007). Both
are set to unity for these cool and small planets (Bolmont
et al. 2017). The mean density of the planets was calcu-
lated using masses derived from TTV in Gillon et al. 2017
(See Table 1). We consider here that the atmospheres of
the planets are mainly composed of hydrogen and oxy-
gen and compute their joint escape using the formalism
of Hunten et al. (1987). The escape rates of both ele-
ments depend on the temperature of the thermosphere,
the gravity of the planet and a collision parameter be-
tween oxygen and hydrogen. As in Bolmont et al. (2017)
and Ribas et al. (2016), we adopt a thermosphere tem-
perature of 3000 K obtained through our hydrodynamic
simulations. We caution that more detailed models, in-
cluding FUV radiative transfer, photochemical schemes,
and non-LTE kinetics in the rarefied gas regions of the
upper atmosphere, will be required to determine accu-
rately the outflow properties. For example the hydrody-
namic outflow of hydrogen could drag water molecules,
which are only slightly heavier than oxygen atoms, up-
ward and they would be photodissociated at high alti-
tudes into more escaping oxygen and hydrogen atoms.
Nonetheless, our assumptions likely maximize the XUV-
driven escape (see Bolmont et al. 2017), and our esti-
mates of the water loss should be considered as upper
limits.
4.2. Estimation of the planets’ XUV irradiation
To calculate the planetary mass losses, we needed
estimations of the XUV irradiation from TRAPPIST-1
over the whole history of the system. In a first step,
we calculated the present day stellar irradiation. We
used the same value as in Bourrier et al. (2017) for the
X-ray emission (5–100 ˚A ), studied by Wheatley et al.
(2017). The stellar EUV emission between 100–912 ˚A
is mostly absorbed by the ISM but can be approxi-
mated from semi-empirical relations based on the Ly-α
emission. The theoretical Ly-α line profile derived for
Visit 4 (Sect. 3.2) yields an upper limit on the total
Ly-α emission of 7.5±0.9×10−2
erg s−1
cm−2
at 1 au.
This is larger than the emission derived for previous
visits (5.1
+1.9
−1.3 ×10−2
erg s−1
cm−2
, B17), in agreement
with the increase in flux suggested by observations
(Sect. 3.1). We chose to consider those two estimates as
9. Irradiation and water loss of TRAPPIST-1 exoplanets 9
Table 3
Age at which the TRAPPIST-1 planets enter the HZ for two different hypothesis: a synchronized planet (Sp = 1.5 S⊕) and a
non-synchronized planet (Sp = 0.84 S⊕).
Assumption THZ (Myr)
on HZ limit planet b planet c planet d planet e planet f planet g planet h
Sp = 1.5 S⊕ – – 461 211 107 65 33
Sp = 0.84 S⊕ – – – 494 218 135 67
lower and upper limits on the present Ly-α emission of
TRAPPIST-1, and used the Linsky et al. (2014) relation
for M dwarfs to derive corresponding limits on the EUV
flux. Table 4 gives our best estimate for today’s range
of fluxes emitted by TRAPPIST-1 at Ly-α and between
5 - 912 ˚A. We computed the ratio of these two fluxes
to the bolometric luminosity and obtained a value of
log10(LXUV/Lbol) between -3.39 and -3.73, which is
about a factor 2.5 lower than estimated from the X-ray
flux by Wheatley et al. (2017).
In a second step, we estimated the past stellar irradia-
tion. We consider that when the planets were embedded
in the protoplanetary disk, they were protected from irra-
diation and did not experience mass loss. In that frame,
water loss began at the time when the disk dissipated,
which we assume to be 10 Myr (Pascucci et al. 2009;
Pfalzner et al. 2014; Pecaut & Mamajek 2016). We in-
vestigated two different scenarios, depending on our as-
sumptions for the temporal evolution of the XUV emis-
sion after the disk dissipation:
- A constant LXUV equal to today’s range of emis-
sion. This assumption might be supported by the
X-ray flux of TRAPPIST-1, which is consistent
with a saturated emission typical of earlier type
M-dwarfs, according to Wheatley et al. 2017).
- An evolving LXUV, considering the ratio
LXUV/Lbol to be constant throughout the
history of the star. The ratio was set to the
present day estimate of the star luminosities (see
Table 4). We used the evolutionary models of
Baraffe et al. (2015) to compute the evolution of
the bolometric luminosity.
Here we set the stellar mass to its nominal value of
0.091 M . Considering the range allowed by the uncer-
tainties would slightly change our water loss estimates,
at the time the planet reached the HZ for the constant
XUV flux prescription, and at all ages for the evolving
XUV flux prescription. We estimate that the difference
would be less than 4% at an age of 8 Gyr.
4.3. Water loss evolution
Using the energy-limited model in Sect. 4.1 and our
estimates for the XUV irradiation in Sect. 4.2, we
calculated the mass loss from TRAPPIST-1 planets
over time. In order to calculate the hydrogen loss,
we used the method (2) of Ribas et al. (2016), which
consists in calculating the ratio between the oxygen and
hydrogen fluxes as a function of the XUV luminosity.
We consider here an infinite water reservoir. This
allows us to consider that the ratio of hydrogen and
oxygen remains stoichiometric even though the loss is
not stoichiometric. This provides us with an upper limit
on the mass loss (see Ribas et al. 2016 for a discussion
on the effect of a finite initial water reservoir). The
loss is given in units of Earth Ocean equivalent content
of hydrogen (referred as 1 EOH). In other words, the
mass loss is expressed in unit of the mass of hydrogen
contained in one Earth ocean (1.455 × 1020
kg, with an
Earth ocean mass corresponding to 1.4×1021
kg). For
example we estimate a current mass loss from planet b of
0.008 Mocean/Myr, for the nominal XUV flux (Table 4).
This corresponds to escape rates of oxygen and hydro-
gen from planet b of 2.9 × 108
g/s and 4.3 × 107
g/s,
respectively. The values for the other planets can be
found in Table 5. Figure 10 shows the evolution of
the hydrogen loss from the TRAPPIST-1 planets as a
function of the age of the system in the two scenarios
assumed for the evolution of the XUV flux. Table 6 gives
the corresponding mass loss at different times of interest.
Planet b and c never reach the HZ, so they are
expected to have lost water via the runaway greenhouse
mechanism (Sect. 4) throughout the full lifetime of
the star. If TRAPPIST-1 is 3 Gyr old (the lower
estimate of the age given in Luger et al. 2017), planet
b potentially lost more than 20 EOH and planet c
more than 10 EOH. If planets b and c formed with
an Earth-like water content, they are likely dry today,
whatever the assumptions on the XUV flux and the age
of the star. Alternatively they might have formed as
ocean planets (L´eger et al. 2004), in which case a loss of
20 Earth oceans for planet b would represent only 0.5%
of its mass. Currently this scenario is not favoured by
the planet formation model proposed by Ormel et al.
(2017), which excludes water fractions larger than about
50%, and by the densities of planets b and c derived
observationally by Gillon et al. (2017) and Wang et al.
(2017), although we note that they still allow for a
significant water content.
If we consider that the water loss only occurs during
the runaway phase, planets d to f lost less than 4 EOH
before reaching the HZ, and planets g and h lost less
than 1 EOH. In that scenario the outer planets of the
TRAPPIST-1 system might thus still harbour substan-
tial amounts of water, especially planets e to h if the low
densities derived by Wang et al. (2017) are confirmed.
What if hydrodynamic water loss continued once the
planets reached the HZ? After 3 Gyr, we estimate that
planets g and those closer-in would have lost more than
7 EOH. After 8 Gyr, they would have lost more than
20 EOH (Table 6). Interestingly, the relation obtained
by Guinan et al. 2016 for M0-5 V dwarf stars yields an
age of about 7.6 Gyr for TRAPPIST-1, using the X-ray
flux obtained by Wheatley et al. 2017 in the ROSAT
10. 10 V. Bourrier et al.
Table 4
High-energy emission from TRAPPIST-1.
Wavelength domain XUV (0.5 − 100 nm) Lα
LXUV (erg.s−1) log10(LXUV/Lbol) Lα (erg.s−1) log10(Lα/Lbol)
Lower estimate 5.26 × 1026 -3.58 1.44 × 1026 -4.15
Mean estimate 6.28 × 1026 -3.51 1.62 × 1026 -4.09
Upper estimate 7.30 × 1026 -3.44 1.81 × 1026 -4.05
Table 5
Current mass loss rate, hydrogen loss rate and oxygen loss rate for the TRAPPIST-1 planets.
Planet b c d e f g h
Mass loss (Mocean/Myr) 8.2 × 10−3 2.9 × 10−3 2.3 × 10−3 1.7 × 10−3 1.4 × 10−3 6.4 × 10−4 2.9 × 10−4
Hydrogen loss (g/s) 4.3 × 107 2.3 × 107 1.3 × 107 1.2 × 107 1.1 × 107 1.2 × 107 4.3 × 106
Oxygen loss (g/s) 2.9 × 108 1.0 × 108 8.2 × 107 5.7 × 107 4.7 × 107 1.5 × 107 7.5 × 106
band (0.14 erg s−1
cm−2
at 1 au). This age is at the up-
per limit of the range derived by Luger et al. (2017), and
if confirmed suggests that all TRAPPIST-1 planets have
lost substantial amounts of water over the long history of
the system. Refined estimates of the planet densities will
however be necessary to determine whether they still har-
bour a significant water content. We also note that our
estimates for the water loss once planets are in the HZ
(Table 6) are probably upper limits. If the planet is able
to retain its background atmosphere, the tropopause is
expected to act as an efficient cold trap, preventing water
from reaching the higher parts of the atmosphere (e.g.,
Wordsworth & Pierrehumbert 2014; Turbet et al. 2016).
In that case, water escape would be limited by the dif-
fusion of water through the cold trap. However, if the
background pressure is low, the water vapor mixing ratio
increases globally in the atmosphere (Turbet et al. 2016)
and hydrogen escape is no longer limited by the diffusion
of water. The farther out the TRAPPIST-1 planets, the
more likely there would have been able to sustain an
important background atmosphere, thus protecting the
water reservoir once in the HZ.
4.4. Consequences of the uncertainty on the planetary
masses
While the radii of the TRAPPIST-1 planets are
known to a good precision, their masses remain very
uncertain. We set today’s XUV luminosity to the
nominal estimate in Table 4, and investigated the effect
of changing the value of the planetary mass within the
range of uncertainty estimated by Gillon et al. (2017)
(see Table 1). For planet h, we investigated a range
of compositions from 100% ice to 100% iron, which
corresponds to masses between 0.06 M⊕ and 0.86 M⊕.
Figure 11(b) shows that for most planets the uncertainty
on their mass dominates the final uncertainty on the
mass loss, compared to the effect of varying the XUV
irradiation with its uncertainty (see also Luger &
Barnes 2015). This is because hydrogen loss is not only
inversely proportional to the planetary mass (see Eq.
1), but is also linked to the ratio of the escape fluxes
of hydrogen and oxygen (rF = FO/FH), which is a
function of the cross-over mass (see Hunten et al. 1987;
Bolmont et al. 2017). For a given value of the XUV
luminosity and an infinite initial water reservoir, the
hydrogen mass loss is described by a polynomial in Mp
of the form α/Mp + βMp, where α and β are constants
depending, for example, on the radius of the planet (we
refer to Eqs. 8 and 9 of Bolmont et al. 2017 to derive
these values). The mass flux decreases with increasing
planetary mass and the ratio of the flux of oxygen over
the flux of hydrogen decreases with increasing planetary
mass. For high masses, the mass flux is lower (gravity
wins over cross section) but the mass loss mainly occurs
via hydrogen escape. This results in a high hydrogen
escape rate. For low masses, the outflow is a mixture
of hydrogen and oxygen, meaning less hydrogen escape
for an equal energy input, but the overall mass flux is
higher. For low enough mass, the increased overall mass
flux does more than compensate and this also results
in a high hydrogen loss. The hydrogen loss is therefore
high for very low mass and very high mass planets with
a minimum for intermediate mass. Figure 11(a) shows
this dependance of the hydrogen flux with mass for
each planet of the system. For all planets but planet
b, the minimum loss is achieved for an intermediate
mass in the range allowed by the observations (this
range is displayed as a thicker line on the graph). The
lower curves delimiting the colored areas in Figure 11(b)
correspond to the hydrogen loss calculated for this
intermediate mass for all planets but b. For planet b,
the minimum hydrogen loss is obtained for the highest
mass allowed by the observations.
In the end the uncertainty on the hydrogen loss comes
mainly from the uncertainty on mass rather than the
uncertainty on the prescribed luminosity (although we
note that our calculations assume an unlimited water
supply, yielding upper limits on the water losses; see
Sect. 4.3). The uncertainty on the hydrogen loss thus
ranges from about 80% for planets b and e, ∼ 50% for
planets d and h, ∼20% for planet c and g and only 4%
for planet f. Table 7 gives the upper and lower estimates
of hydrogen loss for the mass range for each planet and
for the different times considered in this study. Due
to the relative precision of the mass of planet f, the
mass loss is relatively well constrained with our model,
with a loss of less than 0.5 EOH before reaching the
HZ and less than 20 EOH at an age of 8 Gyr. Given
that the low density of planet f is compatible with a
11. Irradiation and water loss of TRAPPIST-1 exoplanets 11
Hydrogenloss(EOH)Hydrogenloss(EOH)
b c d
e
f
g
h
Ls range
Time (Myr)
20
15
10
5
0
0 2000 4000 6000 8000
20
15
10
5
0
(a) Constant XUV luminosity Hydrogenloss(EOH)Hydrogenloss(EOH)
b c d
e
f
g
h
Ls range
0.091
Time (Myr)
20
15
10
5
0
0 2000 4000 6000 8000
20
15
10
5
0
(b) Evolving XUV luminosity
Figure 10. Cumulative hydrogen loss for the TRAPPIST-1 planets for the two different assumptions for the evolution and values of
the XUV flux (see Table 4). The masses of the planets are the masses from Table 1. Because of our assumptions, these estimates likely
represent upper limits on the actual loss.
non negligible water content (Gillon et al. 2017), this
could indicate that water loss may not have been a very
efficient process and/or that the planet formed with a
large fraction of its mass in water.
We note that for most planets, the estimates of the
masses from Wang et al. (2017) are more precise but
consistent compared to Gillon et al. (2017). However,
for planet f, the mass ranges obtained by these different
studies are incompatible, and using the mass from Wang
et al. (2017) would lead to a higher mass loss than what
is shown on Figure 11(b). More data is needed to refine
our measurements of the masses of the planets of the
system.
5. HYDROGEN LOSS VS HYDROGEN PRODUCTION
5.1. Photolysis
The atmospheric mass loss can be limited by the
amount of hydrogen formed by photo-dissociation of wa-
ter molecules. We computed the rate of hydrogen pro-
duction driven by the FUV part of the spectrum, which
is taken to be restricted to the Ly α emission (as in Bol-
mont et al. 2017). We note that water molecules could
further be dissociated through impact with high-energy
electrons, in particular those produced by the ioniza-
tion of water (considering the high X-ray emission of
TRAPPIST-1 and the large ionization cross-section of
water in the XUV; Heays et al. 2017). Figure 12 shows
the hydrogen loss for the nominal irradiation (Table 4)
and planet masses, and the hydrogen quantity available
due to photo-dissociation of water for two different effi-
ciencies: α = 1 (each photon leads to a dissociation, see
Bolmont et al. 2017) and 0.2. We obtained the following
results for a constant XUV luminosity:
1. For planets b and c, photo-dissociation is not the
limiting process for high efficiencies. The hydro-
gen loss is limited by the hydrodynamic escape as
computed in the previous section;
2. For planets d to g, photo-dissociation is the lim-
iting process whatever the efficiency: the rate of
hydrogen formation by photo-dissociation is below
the escape rate of hydrogen.
Photo-dissociation of water also becomes the limiting
process for planets b and c if α <∼ 0.60. Because of
various processes, such as photon backscattering or re-
combination of hydrogen atoms, only a fraction of the
incoming FUV photons actually results in the loss of a
hydrogen atom. As a result we do not expect photo-
dissociation to be more efficient than 20% (Bolmont et al.
2017). It should be the limiting process for all planets,
and the mass losses estimated in Sect. 4 can be considered
as upper limits. The quantity of hydrogen avaible from
photolysis assuming a 20% efficiency is given in Table 8
for each planet, to be compared with the hydrodynamic
hydrogen loss. We note that the photolysis process does
not depend on the mass of the planets (only on their
radii, known to a high precision for the TRAPPIST-1
planets), so these results are more robust than the hy-
drogen loss estimates, which highly depend on the mass
of the planets.
5.2. Outgassing
Water is contained within a rocky planets mantle in
the form of hydrated minerals, as unbound fluids, or
in melt. This water can be released to the surface
through volcanic activity. Such outgassing processes are
very different during the early stages of planet evolution
12. 12 V. Bourrier et al.
Table 6
Cumulative hydrogen loss (in EOH ) for different times (table corresponding to Fig. 10). THZ is the age at which a planet enters in the
HZ (see Table 3). The two values given for each column correspond to the uncertainty coming from the different luminosity prescriptions
(between low and high, see Table 4).
H loss (EOH )
Planet Mass THZ THZ 3 Gyr 8 Gyr
(M⊕) (1.5 S⊕) (0.84 S⊕)
LXUV evol b 0.85 – – 29.2–35.4 71.5–86.9
c 1.38 – – 15.2–17.6 38.1–44.1
d 0.41 2.35–2.87 – 9.12–11.2 22.2–27.2
e 0.62 1.20–1.46 2.05–2.49 7.98–9.57 19.6–23.4
f 0.68 0.70–0.86 1.14–1.39 7.46–8.89 18.4–21.8
g 1.34 0.31–0.37 0.58–0.67 7.79–8.46 20.1–21.7
h 0.46 0.07–0.09 0.14–0.17 2.91–3.23 7.40–8.15
LXUV cst b 0.85 – – 25.3–30.7 67.5–82.1
c 1.38 – – 13.7–15.8 36.5–42.1
d 0.41 1.17–1.44 – 7.80–9.57 20.8–25.5
e 0.62 0.47–0.56 1.12–1.34 6.95–8.28 18.6–22.1
f 0.68 0.21–0.25 0.45–0.54 6.52–7.70 17.4–20.6
g 1.34 0.14–0.15 0.31–0.33 7.34–7.89 19.6–21.1
h 0.46 0.02–0.02 0.05–0.06 2.69–2.94 7.18–7.86
Table 7
Cumulative hydrogen loss (in EOH ) for different times. THZ is the age at which a planet enters in the HZ (see Table 3). The two values
given for each column correspond to the uncertainty coming from the masses (for the mean estimation of the XUV luminosity, see
Table 4).
Mass H loss (EOH ) Uncertainty
Planet range THZ THZ 3 Gyr 8 Gyr range
(M⊕) (1.5 S⊕) (0.84 S⊕) %
LXUV cst b 0.13–1.57 – – 18.8–160 50.3–429 79
c 0.77–1.99 – – 14.5–19.2 38.6–51.3 14
d 0.14–0.68 1.04–3.16 – 6.97–21.0 18.6–56.0 50
e 0.04–1.20 0.49–5.21 1.17–12.5 7.26–77.6 19.4–207 83
f 0.50–0.86 0.23–0.25 0.48–0.55 6.99–7.88 18.7–21.0 6
g 0.46–2.22 0.12–0.19 0.28–0.43 6.60–10.3 17.6–27.5 22
h 0.06–0.86 0.02–0.05 0.05–0.13 2.59–6.84 6.92–18.3 45
Table 8
Hydrogen loss and hydrogen production (in EOH ) for different times. The two values given for each column correspond to the quantity of
hydrogen lost (calculated for the nominal estimate of the XUV luminosityin Table 4, and the nominal masses) and the quantity of
hydrogen available from photolysis (in bold, assuming an efficiency of 20%).
H loss (EOH )
Planet Mass THZ THZ 3 Gyr 8 Gyr
(M⊕) (1.5 S⊕) (0.84 S⊕)
LXUV evol b 0.85 – – 32.4–13.0 79.5–28.6
c 1.38 – – 16.5–6.54 41.2–14.4
d 0.41 2.62–0.65 – 10.2–1.76 24.8–3.88
e 0.62 1.33–0.39 2.28–0.55 8.79–1.44 21.6–3.18
f 0.68 0.79–0.21 1.27–0.29 8.19–1.08 20.1–2.38
g 1.34 0.34–0.12 0.63–0.19 8.13–0.85 20.9–1.87
h 0.41 0.08–0.02 0.16–0.03 3.07–0.20 7.78–0.43
LXUV cst b 0.85 – – 28.1–9.30 75.0–24.8
c 1.38 – – 14.8–4.69 39.4–12.5
d 0.41 1.31–0.19 – 8.70–1.26 23.2–3.37
e 0.62 0.51–0.07 1.23–0.17 7.63–1.03 20.4–2.76
f 0.68 0.23–0.02 0.50–0.05 7.12–0.77 19.0–2.06
g 1.34 0.14–0.01 0.32–0.03 7.62–0.61 20.3–1.62
h 0.41 0.02–<0.01 0.05–<0.01 2.82–0.14 7.52–0.37
13. Irradiation and water loss of TRAPPIST-1 exoplanets 13
b c d e f g h
Normalizedhydrogenflux
Planet mass (M⨁)
1.00
0.10
0.1 1.0 10.0
0.01
(a) Effect of mass on the hydrogen flux
Hydrogenloss(EOH)Hydrogenloss(EOH)
Time (Myr)
b
c
d
e f
g
h
Mp range
20
15
10
5
0
0 2000 4000 6000 8000
20
15
10
5
0
(b) Hydrogen loss for the observational mass range
Figure 11. Effect of planetary mass on the hydrogen loss for the TRAPPIST-1 planets, for the range of masses in Gillon et al. (2017).
The XUV flux is set to its nominal estimate (LXUV = cst) (a) Normalized hydrogen flux as a function of planetary mass for the different
planets. The thick part of each curve corresponds to the allowed range determined by Gillon et al. (2017) and the vertical line corresponds
to the mass which corresponds to the lowest hydrogen flux. (b) Hydrogen loss from the planets. The thicker line corresponds to the loss
calculated for the mass given in Gillon et al. (2017) and the thin lines correspond to the lower and upper estimation within the mass range
given in the same article.
14. 14 V. Bourrier et al.
Hydrogenloss(EOH)Hydrogenloss(EOH)
Time (Myr)
b c d e f g h
Hydrogen loss
Hydrogen available
from photolysis
LXUV = cst
Nom123
1, 0.2 eff
20
15
10
5
0
0 2000 4000 6000 8000
20
15
10
5
0
Figure 12. Hydrogen loss (full lines) and hydrogen production
(dashed lines) by photolysis for the planets of TRAPPIST-1. The
amount of hydrogen formed by photolysis was calculated for two
efficiencies of the process: 1 (upper dashed lines) and 0.2 (lower
dashed lines). With a realistic value of the photolysis efficiency,
we find that photolysis is the limiting process as the hydrogen loss
cannot occur faster than the hydrogen production.
(< 10-100 Myr, see Solomatov 2007), where the surface
and a significant fraction of the planets mantle could be
molten (magma ocean phase), and a later stage, where
the largest fraction of the planet’s mantle is solid. In
the following sections, we will discuss the amounts of
outgassed water during the magma ocean phase of the
TRAPPIST-1 planets, assuming they are rocky, and we
compute the water outgassing rates for the later stage of
subsolidus convection as a function of time.
5.2.1. Outgassing from a magma ocean
At the early stages of planet evolution, magma oceans
can outgas large fractions of water. The amount of out-
gassed water can range from less than 1% to 20% of
a terrestrial-like planet mass based on typical composi-
tions (see Elkins-Tanton & Seager 2008). For the Earth
(MEarth = 5.972×1024
kg), this would correspond to up
to 800 oceans of water assuming chondritic CI mete-
orites as the planet’s building blocks. This number is
clearly an upper limit, considering the fact that the Earth
(and possibly the planets in the TRAPPIST-1 system),
might have formed from much drier (intermediate size)
planetary bodies or lost significant amounts of water in
the impact-driven formation processes. Furthermore, the
model of Hamano et al. (2013) suggests that planets with
steam atmospheres at orbits with a stellar influx larger
than about 300 W m−2
(the Earths current incoming
solar radiation) would have much longer magma ocean
phases and could hence possibly outgas much more of
their initial water at an early stage in the first few 10-
100 Myr, and thus end up much drier than planets at
greater distances from their host star. Based on the heat
fluxes for the TRAPPIST-1 planets today (see Gillon
et al. 2017), planets b-d would fall in orbits with such
elevated heat fluxes. However, at this point in time, it is
almost impossible to estimate the initial water inventory
after the planet formation phase (including magma ocean
and a possible later delivery of water), because of a lack of
detailed understanding of what the early radiation envi-
ronment of TRAPPIST-1 looked like, whether the plan-
ets migrated inwards from a greater distance during this
epoch (at subcritical lower stellar flux levels), whether
any of the planets had a steam atmosphere (hydrogen-
and methane-rich atmospheres would have no outgoing
radiation limit to slow cooling, see Elkins-Tanton 2013;
and hence not fall under the Hamano et al. 2013 di-
chotomy), and whether any water was delivered by im-
pactors after the magma ocean phase. Therefore, what
we can constrain at this point in time are the limits to
the outgassed amount of water during the magma ocean
phase, and the later maximum subsolidus outgassing of
water assuming plausible ranges of post-magma-ocean
water content in the planets mantles (see next sections).
5.2.2. Outgassing after the magma ocean phase
After the magma ocean phase, rocky planets cool
mainly through subsolidus convection and outgas water
through volcanism. Volcanic activity and outgassing are
driven by the formation and transport of melt within the
planet’s subsurface, which depend on the thermal profile,
the melting temperature of rock, and on the advective
transport of rock parcels within a planets lithosphere.
5.2.3. Methods
Melt is formed only where the temperature exceeds
the melting temperature of rock. We, therefore, have to
model 1) the interior depth-dependent thermal evolution
of a planet and know 2) the melting curve of mantle rock
in order to assess a planet’s ability to generate melt.
1. The thermal histories of planets are computed
with an extended 1D boundary layer model (Sta-
menkovi´c et al. 2012), which agrees well with spher-
ical 2D thermal evolution models (i.e., H¨uttig &
Stemmer 2008). The thermal evolution is described
by two thermal boundary layers, which drive ther-
mal convection and are used to parameterize the
heat flux out of the core and out of the convective
mantle, which is fed by secular cooling and radio-
genic heat sources decaying in time. For simplicity,
we assume the Earth’s radiogenic heat content to
obtain a first insight into the TRAPPIST-1 plan-
ets; we do not expect our conclusions to signifi-
cantly vary for alternative values based on some
first tests.
We try to mimic an initially fully molten man-
tle by fitting the initial upper mantle tempera-
ture Tm(0) to the solidus temperature of peridotite,
Tmelt,peridotite (see below). For the highest initial
15. Irradiation and water loss of TRAPPIST-1 exoplanets 15
core-mantle boundary (CMB) temperature, Tc(0),
we use the melting temperatures of MgSiO3 per-
ovskite from Stamenkovi´c et al. (2011). This as-
sumption allows us to fluently connect to an ini-
tial early magma ocean stage. All scaling relations
and parameters can be found in Stamenkovi´c et al.
(2012).
2. Our melt model has been described in detail in Sta-
menkovi´c & Breuer (2014) and for the melting tem-
perature in the upper mantle (where the melt that
drives outgassing is produced) uses the solidus for
Earth-like peridotite, Tmelt,peridotite. Tmelt,peridotite
is obtained by fitting the data from Herzberg et al.
(2000), Zerr et al. (1998), and Fiquet et al. (2010)
(see Eq. 7 in Stamenkovi´c & Breuer 2014).
Water can have a significant effect on reducing the
solidus temperature of mantle rock (e.g., Asimow
et al. 2004; Aubaud et al. 2004; Grove et al. 2009;
Hirschmann 2006). Asimow et al. (2004) com-
pute melting curves for water-under-saturated and
water-saturated peridotite. Their water-saturated
melting curve is close to a prediction based on the
homologous temperature approach (for details, see,
e.g., Katayama & Karato 2008; Stamenkovi´c et al.
2011). In the homologous temperature model, the
melting temperature change corresponds to the en-
thalpy change of diffusion creep, E∗
, (at smaller
pressures approximately activation energy change),
so that Tmelt,dry/Tmelt,wet = E∗
dry/E∗
wet. This cor-
responds to a melting point reduction of ∼20%
due to water saturation when we use the model
of Karato & Wu (1993) for activation energies of
dry and wet olivine. We, therefore, use our water-
saturated homologous temperature based melting
curve as the reference melting curve for water-
saturated upper mantle rock.
The upper mantle water concentrations are thought
to generally be below water saturation levels, typically
between 50-200 ppm (partially up to 1000 ppm, still
not saturated) (Aubaud et al. 2004; Hirschmann 2006),
at subduction zones locally over-saturated (e.g., Grove
et al. 2009), and plumes are found to contain about
300-1000 ppm of water (Hirschmann 2006 for review).
The storage capacity of olivine on the other hand has
been estimated to increase with depth from ∼25 ppm at
10 km to ∼1300 ppm at 410 km for the Earth, strongly
varying with water fugacity and hence temperature and
depth. It is, however, possible that this value is about
∼3-3.5 times too small, leading to more than ∼0.4
weight % of water for mantle rock (see Hirschmann 2006
and references therein). On the other hand, based on
geochemical constraints on K2O/H2O ratios in basalts
(Hirschmann 2006 for review), the bulk water content
is estimated to be between 500-1900 ppm. For our first
order of magnitude estimate for the TRAPPIST-1 sys-
tem, we assume no depth-dependence of water content
or storage capability and use average bulk values of
500 ppm (minimal value bulk mantle) to 0.4% (upper
saturation value) for mantle rock. The rheology is fixed
to a Newtonian-type viscosity for a wet bulk mantle
based on Karato & Wu (1993).
We vary the pressure dependence (activation volume
V∗
) of the mantle viscosity, from V∗
=0 to values
calculated in Stamenkovi´c et al. 2011. We propagate
this uncertainty in mantle viscosity throughout all
calculations. Furthermore, we follow the probabilistic
approach of Stamenkovi´c & Seager (2016), where we
also propagate an uncertainty in our heat flux (Nusselt)
scaling parameter β, allowing it to vary between 0.2-1/3.
By accounting for all uncertainties, we make sure that
our results are as robust as possible. Within this
parameter space, we highlight a favored model with a
value of β ∼0.3 for the Nusselt-Rayleigh parameter and
a pressure-dependent activation volume as computed
in Stamenkovi´c et al. (2011) suggesting that this
standard model best represents the thermal evolution of
rocky planets of variable core size between 0.1-2 Earth
masses representative of the possible refractory planet
masses for the TRAPPIST-1 planets. We fix the surface
temperature to 298 K, as surface temperature variations
found in the TRAPPIST-1 system today (unless above
many 100 K close to the magma ocean phase) have no
impact on the interior evolution.
Knowing a planet’s ability to generate melt at depth
and in time is however not sufficient to calculate whether
that parcel of melt can be brought to the surface leading
to potential outgassing. The latter depends strongly on
two factors, 1) the density cross-over pressure of mantle
rock and 2) the tectonic mode of a planet.
1. Melt generated at depth will rise to the surface as
long as the density of melt is smaller than that of
the surrounding solid rock. However, on the Earth
typical mantle rock at pressures above 12 GPa does
not rise to the surface due to the density-cross over,
where melt becomes denser than surrounding solid
rock (Ohtani et al. 1995). We note that this pres-
sure value of 12 GPa varies with rock composition
and especially water content (Jing & ichiro Karato
2009). Hence, we use the terrestrial value only as
a reference point to explore whether the density
cross-over pressure might affect outgassing on the
TRAPPIST-1 planets. Moreover, we do not ac-
count for any other mechanisms that could cause
intrusive volcanism.
2. The tectonic mode has two end members: plate tec-
tonics (PT), as found on the Earth, and stagnant
lid (SL) convection, as found on modern-day Mars.
In the following, we will model outgassing for stag-
nant lid planets. Modeling outgassing in the plate
tectonics mode is too sensitive to planet properties
that we do not yet know from the TRAPPIST-1
planets, and hence we leave this to future work
and refer to Schaefer & Sasselov (2015) for a more
detailed discussion on outgassing on plate tectonics
worlds.
For the TRAPPIST-1 planets, the uncertainties in
mass are yet too large to infer much structural or compo-
sitional detail. At this point in time, what we can do is
model the thermal evolution, melt generation, and water
outgassing assuming a terrestrial (refractory) planetary
body with a mass between 0.1-2 Earth masses with vari-
able iron core sizes from 0-65% (corresponding to core-
16. 16 V. Bourrier et al.
less to Mercury-structured) in the stagnant lid mode -
and put the TRAPPIST-1 planets in context with these
results. Also, we note that we do not include tidal heat-
ing at this point in time. To make significant conclusions
about the effects of tidal heating on the thermal evolu-
tion of the TRAPPIST-1 planets, we need much better
constraints on planet masses, their volatile content, and
their structures. Therefore, better constraints on planet
masses will significantly improve our predictions in the
near future.
5.2.4. Results
We find that after the magma ocean phase, the
TRAPPIST-1 planets can outgas significant amounts of
water, especially the more massive ones. We show in
Fig. 13 - whilst accounting for significant uncertainties
in structure and model parameters - the range of mini-
mal planet ages where outgassing can occur as a function
of planet mass. Within this domain, we also plot the so-
lution for our standard model (in pink) without and with
consideration of the density cross-over at 12 GPa. We see
in Fig. 13 that the minimal ages during which outgassing
can occur vary largely (mainly modulated by core frac-
tion and Nusselt-Rayleigh parameter uncertainty). How-
ever, our standard model shows a robust behavior, in-
dependent of density crossover, suggesting that planets
formed from more massive refractory parent bodies will
be able to outgas much longer. Fig. 14 (showing the out-
gassed amount of water, in Earth oceans, for 500 ppm
and 0.4 weight % of water respectively) also exemplifies
that planets with more massive refractory parent bodies
can outgas more water and outgas that water at much
later times in their evolution.
Combining this finding with Fig. 9, which shows
that planets within the orbits of TRAPPIST-1d and
TRAPPIST-1h enter the HZ within 100 Myr to a
few hundred Myr, and considering that the largest
atmospheric loss processes occur before entering the
HZ, suggests that especially planets farther away from
TRAPPIST-1 and planets that are more massive could
deliver up to 1-2 ocean masses of water after they entered
the HZ. This emphasizes that late-stage geophysical out-
gassing might be a critical component helping to sustain
habitable environments within the TRAPPIST-1 system.
0 0.5 1 1.5 2
Planet Mass [MEarth
]
0
2
4
6
8
Time[Gyr]
0 0.5 1 1.5 2
Planet Mass [MEarth
]
0
2
4
6
8
Time[Gyr]
b)a)
Figure 13. Duration of outgassing: As a function of refractory
planet mass, we show the minimal duration of outgassing with-
out (a) and with (b) consideration of an Earth-like reference den-
sity cross-over, including all uncertainties specified in the methods
(Sect. 5.2.3) in shaded blue. This uncertainty range is reduced to
the domain in between the pink lines when considering only our
standard model. When the density cross-over is considered, more
massive planets can lack any extrusive volcanism due to the melt
source region being too deep (and hence at too high pressures).
However, for our standard model, we find that for all cases, more
massive planets can outgas longer.
0 2 4 6 8
Time [Gyr]
0
0.5
1
1.5
2
2.5
3
OceanMass[1.41021
kg]
0 2 4 6 8
Time [Gyr]
0
0.1
0.2
0.3
0.4
OceanMass[1.41021
kg]
b)a)
Figure 14. Outgassed water: We plot the range for the amount of
outgassed water as a function of planet age for planets of refractory
planet mass M=0.1 (red), 1 (blue), and 2 (green). The two col-
ored lines delimit in each case the range of uncertainties in planet
structure (from core-less to Mercury-structured) for our standard
model. Figure (a) assumes 500 ppm of water in the planets mantle
and (b) saturation levels of 0.4 weight %.
6. DISCUSSION
We observed the Ly-α line of TRAPPIST-1 with
HST/STIS in December 2016, at the time of planet c
transiting. When compared with previous observations
obtained in September and November 2016, this new
measurement revealed that the stellar line evolved
significantly in the last visit. It shows an increased
emission with broader wings, which might trace an
increase in the temperature of the stellar chromosphere.
The relation from Youngblood et al. (2016) between
the stellar rotation period and Ly-α surface flux of
early-type M dwarfs predicts significantly stronger Ly-α
emission than we detected for TRAPPIST-1. Our
measured Ly-α fluxes would correspond to rotation
periods of ∼84 days (based on Visits 1-3 Ly-α flux)
and ∼54 days (based on Visits 4 Ly-α flux), whereas
the rotation period from from K2 photometric data
is ∼3.3 days (Luger et al. 2017). This is in contrast
to our detection of Nv emission, which we find to be
consistent with the previously measured X-ray flux.
Together these observations support our hypothesis that
TRAPPIST-1 has a weak chromosphere compared to its
transition region and corona (Wheatley et al. 2017, B17).
The spectra in December 2016 are subjected to a
strong airglow contamination, which could have biased
the extraction of TRAPPIST-1 Lyman-α line. Nonethe-
less, a careful analysis of the stellar line shape tentatively
suggests an absorption from neutral hydrogen at high
velocity in the blue wing. This signature does not seem
to correlate with the transit of TRAPPIST-1c, but
could originate from a system-wide neutral hydrogen
cloud sustained by the evaporation of several planets,
and shaped by the very low radiation pressure and
photoionization from TRAPPIST-1. Alternatively,
the peculiar shape of TRAPPIST-1 Ly-α line in this
epoch could result from physical mechanisms specific or
magnified in ultracool dwarfs. In any case the long-term,
and possibly short-term variability in the intrinsic Ly-α
line of TRAPPIST-1 prevents us from constraining
the presence of a putative hydrogen exosphere around
planet c, and calls for an ongoing monitoring of the star
both outside and during all planets transits.
Combining all measurements of TRAPPIST-1 Ly-α
and X-ray emissions, we estimated the present day XUV
irradiation of the planets. Using simple assumptions
on the evolution of the irradiation over time, we cal-
culated the history of hydrodynamic water loss from
17. Irradiation and water loss of TRAPPIST-1 exoplanets 17
the planets in the energy-limited regime. With our
current knowledge of the TRAPPIST-1 system, the
major uncertainty on the water loss estimates comes
from the uncertainty on the planet masses, rather than
on the XUV luminosity. Setting the masses to their
nominal estimates from Gillon et al. (2017) we found
that planets g and closer-in could have lost more than
20 Earth oceans through hydrodynamic escape, if the
system is as old as 8 Gyr. Planets b, c, and possibly
d could still be in a runaway phase, but if water loss
drops down significantly within and beyond the HZ,
planets e, f, g, and h might have lost less than 3 Earth
oceans. We caution that our water loss estimates were
derived in a simplified framework, and should be con-
sidered as upper limits because our assumptions likely
maximize the XUV-driven escape. We refer the reader
to the section 6 of Bolmont et al. 2017 for more details
about these limitations. Furthermore, we found that
photodissociation of water in the upper atmospheres of
the TRAPPIST-1 planets is likely to be the limiting
process, as hydrogen is produced at a lower rate than
it is lost through hydrodynamic escape rate. Photolysis
efficiency is expected to be lower than about 20%, in
which case all planets but TRAPPIST-1b and c could
still harbor significant amounts of water. Naturally this
also depends on the age of the system and whether the
planets formed with a small water content (as suggested
by planetary formation models, Ormel et al. 2017)
or as planet oceans (as hinted by the low densities
of the outer planets, especially TRAPPIST-1f; Gillon
et al. 2017, Wang et al. 2017). We have also shown
that late-stage outgassing could contribute significant
amounts of water after the planets have entered the HZ.
The amount of water outgassed after a few hundred Myr
(after which TRAPPIST-1h to e, and possibly d, have
entered the HZ), is greater for planets with more massive
refractory parent bodies. Improving our constraints
on the planet masses of the TRAPPIST-1 system will
therefore significantly improve our understanding of the
variable outgassing capabilities of the TRAPPIST-1
planets and hence the current state of their atmospheres.
Our study focused on hydrodynamic water loss driven
by the quiescent stellar XUV irradiation. We also
investigated the effects of photolysis and outgassing,
but we did not account for other physical mechanisms
competing between the erosion of the atmospheres and
their replenishing. For example the presence of other
gases in the atmosphere would act to slow down the
hydrodynamic outflow (just as in our model oxygen
atoms can exert a drag on the hydrogen flow), although
the background atmosphere could also be exposed
to evaporation. We refer the reader to section 5 of
Ribas et al. 2016 for an extensive discussion about the
loss of the background atmosphere and other escape
processes. Stellar flares could occasionally increase
the energy input into the atmospheres, enhancing the
escape rate. However, no flaring activity was observed
in TRAPPIST-1 X-ray and FUV observations, and the
flares detected in optical (Vida et al. 2017, Luger et al.
2017) and infrared (Gillon et al. 2016, Gillon et al. 2017)
wavelengths point toward a low activity, with weak flares
once every few days and stronger flares once every two
to three months. The planetary atmospheres might also
have been eroded by the stellar wind of TRAPPIST-1,
especially when it was more active during the early
phases of the system. Assuming that the planets are
unmagnetized, Dong et al. 2017 derived upper limits on
the atmospheric ion escape driven by the stellar wind.
Tidal heating (due to the planets proximity to the star
and the mutual dynamical interactions maintaining
their slightly eccentric orbits) could maintain significant
magnetospheres, able to protect the planets from a
putative stellar wind, or it could suppress dynamo
activity. Furtheremore, planetary magnetic fields can,
depending on the specific interaction between planet
and star, enhance or reduce atmospheric loss rates
(e.g., Strangeway et al. 2005). Currently we have no
constraints on the ability of the TRAPPIST-1 planets
to generate magnetic fields, as this significantly depends
on planet composition and structure. We also lack
knowledge about the winds of ultracool dwarfs and
their evolution with the stellar magnetic field over time,
although TRAPPIST-1 is so cold that its amosphere
likely has a low level of ionization, resulting in a lower
emission of charged particles than for a hotter star like
Proxima Centauri (e.g. Mohanty et al. 2002).
Understanding the nature of the TRAPPIST-1 planets
and their potential habitability will thus require the
combination of theoretical studies (to better understand
the time-dependent processes leading to geophysically-
driven water outgassing, the atmospheric loss processes,
and the role of magnetic fields in affecting them) with
further photometric observations (to refine the planet
radii and more importantly their masses through TTV),
X-ray and UV observations of the stellar spectrum
(to monitor the activity of the star and measure the
high-energy irradiation of the planetary atmospheres,
currently poorly known; O’Malley-James & Kaltenegger
2017), transit spectroscopy in the FUV (to detect
escaping hydrogen and possibly oxygen) and in the IR
(to search for the signature of water in the bottom
atmospheric layers).
ACKNOWLEDGEMENTS
We give our thanks to the referee for a detailed re-
view and useful suggestions. We thank A. Lecavelier
Des Etangs for insightful discussion about habitability
and extraction of the STIS spectra. We thank S. Ray-
mond, F. Selsis, and H. Wakeford for helpful comments
about this study. This work is based on observations
made with the NASA/ESA Hubble Space Telescope, ob-
tained at the Space Telescope Science Institute, which is
operated by the Association of Universities for Research
in Astronomy, Inc., under NASA contract NAS 5-26555.
This work has been carried out partly in the frame of
the National Centre for Competence in Research “Plan-
etS” supported by the Swiss National Science Foundation
(SNSF). V.B. acknowledges the financial support of the
SNSF. V.S. has received support from the Simons Col-
laboration on the Origins of Life (338555, VS). PW is
supported by STFC consolidated grant ST/P000495/1.
M. Gillon, E. Jehin, and V. Van Grootel are Belgian
F.R.S.-FNRS Research Associates. This work was par-
tially supported by a grant from the Simons Foundation
(PI Queloz, grant number 327127). L. D. acknowledges
18. 18 V. Bourrier et al.
support from the Gruber Foundation Fellowship.
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