Artigo da revista Nature, descreve o trabalho de astrônomos para medir o tamanho e a massa de um exoplaneta parecido com Marte, além de caracterizar por completo o sistema planetário da estrela Kepler-138.
Artigo relata como a Terra sofreu com os impactos de ateroides a 4 bilhões de anos atrás, e como a superfície do planeta foi remodelada e os oceanos formados.
A rocky planet_transiting_a_nearby_low_mass_starSérgio Sacani
Um exoplaneta rochoso do tamanho da Terra, orbita uma estrela pequena e próxima, poderia ser o mundo mais importante já encontrado além do Sistema Solar, disseram os astrônomos.
O planeta localiza-se na constelação de Vela, no hemisfério sul do céu e é próximo o suficiente para que os telescópios possam observar qualquer atmosfera que ele possua, um procedimento que poderia ajudar a registrar algum tipo de vida, se ela existisse em outros planetas, no futuro.
Denominado de GJ 1132b, o exoplaneta é cerca de 16% maior que a Terra, e está localizado a cerca de 39 anos-luz de distância, o que faz com que ele seja três vezes mais próximo da Terra do que qualquer outro exoplaneta rochoso já descoberto. Nessa distância, espera-se que os telescópios sejam capazes de fazer uma análise química de sua atmosfera, a velocidade dos seus ventos e as cores do pôr-do-Sol, que acontecem no exoplaneta.
Os astrônomos registraram o planeta à medida que ele passava na frente da sua estrela, uma estrela do tipo anã vermelha, com somente um quinto do tamanho do Sol. Apesar de muito mais fria e muito mais apagada que o Sol, o GJ 1132b, tem uma órbita tão próxima da estrela que as suas temperaturas superficiais atingem cerca de 260 graus Celsius.
Essa temperatura, obviamente, é muito alta para reter a água em estado líquido na superfície do exoplaneta, fazendo com que ele seja inóspito para a vida, mas não tão quente para queimar toda uma atmosfera que pode ter se formado no planeta.
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.
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.
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.
Artigo relata como a Terra sofreu com os impactos de ateroides a 4 bilhões de anos atrás, e como a superfície do planeta foi remodelada e os oceanos formados.
A rocky planet_transiting_a_nearby_low_mass_starSérgio Sacani
Um exoplaneta rochoso do tamanho da Terra, orbita uma estrela pequena e próxima, poderia ser o mundo mais importante já encontrado além do Sistema Solar, disseram os astrônomos.
O planeta localiza-se na constelação de Vela, no hemisfério sul do céu e é próximo o suficiente para que os telescópios possam observar qualquer atmosfera que ele possua, um procedimento que poderia ajudar a registrar algum tipo de vida, se ela existisse em outros planetas, no futuro.
Denominado de GJ 1132b, o exoplaneta é cerca de 16% maior que a Terra, e está localizado a cerca de 39 anos-luz de distância, o que faz com que ele seja três vezes mais próximo da Terra do que qualquer outro exoplaneta rochoso já descoberto. Nessa distância, espera-se que os telescópios sejam capazes de fazer uma análise química de sua atmosfera, a velocidade dos seus ventos e as cores do pôr-do-Sol, que acontecem no exoplaneta.
Os astrônomos registraram o planeta à medida que ele passava na frente da sua estrela, uma estrela do tipo anã vermelha, com somente um quinto do tamanho do Sol. Apesar de muito mais fria e muito mais apagada que o Sol, o GJ 1132b, tem uma órbita tão próxima da estrela que as suas temperaturas superficiais atingem cerca de 260 graus Celsius.
Essa temperatura, obviamente, é muito alta para reter a água em estado líquido na superfície do exoplaneta, fazendo com que ele seja inóspito para a vida, mas não tão quente para queimar toda uma atmosfera que pode ter se formado no planeta.
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.
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.
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.
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.
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.
Four new planets_around_giant_stars_and_the_mass_metallicity_correlation_of_p...Sérgio Sacani
Exoplanet searches have revealed interesting correlations between the stellar properties and the occurrence rate of planets.
In particular, different independent surveys have demonstrated that giant planets are preferentially found around metal-rich stars and
that their fraction increases with the stellar mass.
Aims. During the past six years, we have conducted a radial velocity follow-up program of 166 giant stars, to detect substellar
companions, and characterizing their orbital properties. Using this information, we aim to study the role of the stellar evolution in
the orbital parameters of the companions, and to unveil possible correlations between the stellar properties and the occurrence rate of
giant planets.
Methods. We have taken multi-epoch spectra using FEROS and CHIRON for all of our targets, from which we have computed
precision radial velocities and we have derived atmospheric and physical parameters. Additionally, velocities computed from UCLES
spectra are presented here. By studying the periodic radial velocity signals, we have detected the presence of several substellar
companions.
Results. We present four new planetary systems around the giant stars HIP8541, HIP74890, HIP84056 and HIP95124. Additionally,
we study the correlation between the occurrence rate of giant planets with the stellar mass and metallicity of our targets. We find that
giant planets are more frequent around metal-rich stars, reaching a peak in the detection of f = 16.7+15.5
−5.9 % around stars with [Fe/H] ∼
0.35 dex. Similarly, we observe a positive correlation of the planet occurrence rate with the stellar mass, between M⋆∼ 1.0 - 2.1 M⊙ ,
with a maximum of f = 13.0+10.1
−4.2 %, at M⋆= 2.1 M⊙ .
Conclusions. We conclude that giant planets are preferentially formed around metal-rich stars. Also, we conclude that they are more
efficiently formed around more massive stars, in the stellar mass range of ∼ 1.0 - 2.1 M⊙ . These observational results confirm previous
findings for solar-type and post-MS hosting stars, and provide further support to the core-accretion formation model.
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.
Bright features have been recently discovered by Dawn on Ceres, which extend
previous photometric and Space Telescope observations. These features should produce
distortions of the line profiles of the reflected solar spectrum and therefore an apparent
radial velocity variation modulated by the rotation of the dwarf planet. Here we report
on two sequences of observations of Ceres performed in the nights of 31 July, 26-
27 August 2015 by means of the high-precision HARPS spectrograph at the 3.6-m
La Silla ESO telescope. The observations revealed a quite complex behaviour which
likely combines a radial velocity modulation due to the rotation with an amplitude of
⇡ ±6 m s
DISCOVERY OF A GALAXY CLUSTER WITH A VIOLENTLY STARBURSTING CORE AT z = 2:506Sérgio Sacani
We report the discovery of a remarkable concentration of massive galaxies with extended X-ray
emission at zspec = 2:506, which contains 11 massive (M & 1011M) galaxies in the central 80kpc
region (11.6 overdensity). We have spectroscopically conrmed 17 member galaxies with 11 from CO
and the remaining ones from H. The X-ray luminosity, stellar mass content and velocity dispersion
all point to a collapsed, cluster-sized dark matter halo with mass M200c = 1013:90:2M, making it
the most distant X-ray-detected cluster known to date. Unlike other clusters discovered so far, this
structure is dominated by star-forming galaxies (SFGs) in the core with only 2 out of the 11 massive
galaxies classied as quiescent. The star formation rate (SFR) in the 80kpc core reaches 3400 M
yr 1 with a gas depletion time of 200 Myr, suggesting that we caught this cluster in rapid build-up
of a dense core. The high SFR is driven by both a high abundance of SFGs and a higher starburst
fraction ( 25%, compared to 3%-5% in the eld). The presence of both a collapsed, cluster-sized
halo and a predominant population of massive SFGs suggests that this structure could represent an
important transition phase between protoclusters and mature clusters. It provides evidence that the
main phase of massive galaxy passivization will take place after galaxies accrete onto the cluster,
providing new insights into massive cluster formation at early epochs. The large integrated stellar
mass at such high redshift challenges our understanding of massive cluster formation.
The characterization of_the_gamma_ray_signal_from_the_central_milk_way_a_comp...Sérgio Sacani
Past studies have identified a spatially extended excess of ∼1-3 GeV gamma rays from the region
surrounding the Galactic Center, consistent with the emission expected from annihilating dark
matter. We revisit and scrutinize this signal with the intention of further constraining its characteristics
and origin. By applying cuts to the Fermi event parameter CTBCORE, we suppress the tails
of the point spread function and generate high resolution gamma-ray maps, enabling us to more
easily separate the various gamma-ray components. Within these maps, we find the GeV excess
to be robust and highly statistically significant, with a spectrum, angular distribution, and overall
normalization that is in good agreement with that predicted by simple annihilating dark matter
models. For example, the signal is very well fit by a 36-51 GeV dark matter particle annihilating to
b
¯b with an annihilation cross section of σv = (1−3)×10−26 cm3
/s (normalized to a local dark matter
density of 0.4 GeV/cm3
). Furthermore, we confirm that the angular distribution of the excess is
approximately spherically symmetric and centered around the dynamical center of the Milky Way
(within ∼0.05◦
of Sgr A∗
), showing no sign of elongation along the Galactic Plane. The signal is
observed to extend to at least ' 10◦
from the Galactic Center, disfavoring the possibility that this
emission originates from millisecond pulsars.
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.
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.
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
Extensive Noachian fluvial systems in Arabia Terra: Implications for early Ma...Sérgio Sacani
Valley networks are some of the strongest lines of evidence for
extensive fluvial activity on early (Noachian; >3.7 Ga) Mars. However,
their purported absence on certain ancient terrains, such as
Arabia Terra, is at variance with patterns of precipitation as predicted
by “warm and wet” climate models. This disagreement has contributed
to the development of an alternative “icy highlands” scenario,
whereby valley networks were formed by the melting of highland ice
sheets. Here, we show through regional mapping that Arabia Terra
shows evidence for extensive networks of sinuous ridges. We interpret
these ridge features as inverted fluvial channels that formed in
the Noachian, before being subject to burial and exhumation. The
inverted channels developed on extensive aggrading flood plains. As
the inverted channels are both sourced in, and traverse across, Arabia
Terra, their formation is inconsistent with discrete, localized sources
of water, such as meltwater from highland ice sheets. Our results are
instead more consistent with an early Mars that supported widespread
precipitation and runoff.
Very regular high-frequency pulsation modes in young intermediate-mass starsSérgio Sacani
Asteroseismology probes the internal structures of stars by using their natural
pulsation frequencies1. It relies on identifying sequences of pulsation modes that can
be compared with theoretical models, which has been done successfully for many
classes of pulsators, including low-mass solar-type stars2, red giants3, high-mass stars4
and white dwarfs5. However, a large group of pulsating stars of intermediate mass—the
so-called δ Scuti stars—have rich pulsation spectra for which systematic mode
identification has not hitherto been possible6,7. This arises because only a seemingly
random subset of possible modes are excited and because rapid rotation tends to
spoil regular patterns8–10. Here we report the detection of remarkably regular
sequences of high-frequency pulsation modes in 60 intermediate-mass
main-sequence stars, which enables definitive mode identification. The space
motions of some of these stars indicate that they are members of known associations
of young stars, as confirmed by modelling of their pulsation spectra.
Measurement of Jupiter’s asymmetric gravity fieldSérgio Sacani
The gravity harmonics of a fluid, rotating planet can be decomposed
into static components arising from solid-body rotation and dynamic
components arising from flows. In the absence of internal dynamics,
the gravity field is axially and hemispherically symmetric and is
dominated by even zonal gravity harmonics J2n that are approximately
proportional to qn, where q is the ratio between centrifugal
acceleration and gravity at the planet’s equator1
. Any asymmetry in the
gravity field is attributed to differential rotation and deep atmospheric
flows. The odd harmonics, J3, J5, J7, J9 and higher, are a measure of the
depth of the winds in the different zones of the atmosphere2,3
. Here
we report measurements of Jupiter’s gravity harmonics (both even
and odd) through precise Doppler tracking of the Juno spacecraft
in its polar orbit around Jupiter. We find a north–south asymmetry,
which is a signature of atmospheric and interior flows. Analysis of
the harmonics, described in two accompanying papers4,5
, provides
the vertical profile of the winds and precise constraints for the depth
of Jupiter’s dynamical atmosphere.
Early optical spectra_of_nova_v1369_cen_show_the_presence_of_lithiumSérgio Sacani
O elemento químico lítio foi encontrado pela primeira vez em material ejetado por uma nova. Observações da Nova Centauri 2013 obtidas com o auxílio de telescópios no Observatório de La Silla do ESO e perto de Santiago do Chile, ajudaram a explicar por que é que muitas estrelas jovens parecem ter mais quantidade deste elemento químico do que o esperado. Esta nova descoberta acrescenta uma importante peça que faltava ao quebra-cabeças que representa a evolução química da nossa Galáxia e é um enorme passo em frente na compreensão das quantidades dos diferentes elementos químicos nas estrelas da Via Láctea.
O elemento químico leve lítio é um dos poucos elementos que se prevê ter sido criado pelo Big Bang, há 13,8 bilhões de anos atrás. No entanto, tentar compreender as quantidades de lítio observadas nas estrelas que nos rodeiam hoje tem sido um processo muito difícil. Estrelas mais velhas possuem menos lítio do que o esperado [1] e algumas estrelas jovens têm dez vezes mais lítio do que o que pensávamos [2].
Desde os anos 1970 que os astrônomos especulam que a enorme quantidade de lítio encontrado nas estrelas jovens poderá vir de novas — explosões estelares que libertam material para o espaço entre as estrelas, contribuindo assim para a matéria que forma a próxima geração de estrelas. No entanto, observações cuidadas de várias novas não tinham, até agora, fornecido resultados claros.
Uma equipe liderada por Luca Izzo (Universidade Sapienza de Roma e ICRANet, Pescara, Itália) utilizou o instrumento FEROS montado no telescópio MPG/ESO de 2,2 metros instalado no Observatório de La Silla, assim como o espectrógrafo PUCHEROS montado no telescópio de 0,5 metros do ESO, no Observatório da Pontificia Universidad Catolica de Chile em Santa Marina, perto de Santiago, para estudar a nova Nova Centauri 2013 (V1369 Centauri). Esta estrela explodiu no céu austral perto da estrela brilhante Beta Centauri em dezembro de 2013, tratando-se, até agora, da nova mais brilhante deste século — facilmente observada a olho nu [3].
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.
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.
Four new planets_around_giant_stars_and_the_mass_metallicity_correlation_of_p...Sérgio Sacani
Exoplanet searches have revealed interesting correlations between the stellar properties and the occurrence rate of planets.
In particular, different independent surveys have demonstrated that giant planets are preferentially found around metal-rich stars and
that their fraction increases with the stellar mass.
Aims. During the past six years, we have conducted a radial velocity follow-up program of 166 giant stars, to detect substellar
companions, and characterizing their orbital properties. Using this information, we aim to study the role of the stellar evolution in
the orbital parameters of the companions, and to unveil possible correlations between the stellar properties and the occurrence rate of
giant planets.
Methods. We have taken multi-epoch spectra using FEROS and CHIRON for all of our targets, from which we have computed
precision radial velocities and we have derived atmospheric and physical parameters. Additionally, velocities computed from UCLES
spectra are presented here. By studying the periodic radial velocity signals, we have detected the presence of several substellar
companions.
Results. We present four new planetary systems around the giant stars HIP8541, HIP74890, HIP84056 and HIP95124. Additionally,
we study the correlation between the occurrence rate of giant planets with the stellar mass and metallicity of our targets. We find that
giant planets are more frequent around metal-rich stars, reaching a peak in the detection of f = 16.7+15.5
−5.9 % around stars with [Fe/H] ∼
0.35 dex. Similarly, we observe a positive correlation of the planet occurrence rate with the stellar mass, between M⋆∼ 1.0 - 2.1 M⊙ ,
with a maximum of f = 13.0+10.1
−4.2 %, at M⋆= 2.1 M⊙ .
Conclusions. We conclude that giant planets are preferentially formed around metal-rich stars. Also, we conclude that they are more
efficiently formed around more massive stars, in the stellar mass range of ∼ 1.0 - 2.1 M⊙ . These observational results confirm previous
findings for solar-type and post-MS hosting stars, and provide further support to the core-accretion formation model.
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.
Bright features have been recently discovered by Dawn on Ceres, which extend
previous photometric and Space Telescope observations. These features should produce
distortions of the line profiles of the reflected solar spectrum and therefore an apparent
radial velocity variation modulated by the rotation of the dwarf planet. Here we report
on two sequences of observations of Ceres performed in the nights of 31 July, 26-
27 August 2015 by means of the high-precision HARPS spectrograph at the 3.6-m
La Silla ESO telescope. The observations revealed a quite complex behaviour which
likely combines a radial velocity modulation due to the rotation with an amplitude of
⇡ ±6 m s
DISCOVERY OF A GALAXY CLUSTER WITH A VIOLENTLY STARBURSTING CORE AT z = 2:506Sérgio Sacani
We report the discovery of a remarkable concentration of massive galaxies with extended X-ray
emission at zspec = 2:506, which contains 11 massive (M & 1011M) galaxies in the central 80kpc
region (11.6 overdensity). We have spectroscopically conrmed 17 member galaxies with 11 from CO
and the remaining ones from H. The X-ray luminosity, stellar mass content and velocity dispersion
all point to a collapsed, cluster-sized dark matter halo with mass M200c = 1013:90:2M, making it
the most distant X-ray-detected cluster known to date. Unlike other clusters discovered so far, this
structure is dominated by star-forming galaxies (SFGs) in the core with only 2 out of the 11 massive
galaxies classied as quiescent. The star formation rate (SFR) in the 80kpc core reaches 3400 M
yr 1 with a gas depletion time of 200 Myr, suggesting that we caught this cluster in rapid build-up
of a dense core. The high SFR is driven by both a high abundance of SFGs and a higher starburst
fraction ( 25%, compared to 3%-5% in the eld). The presence of both a collapsed, cluster-sized
halo and a predominant population of massive SFGs suggests that this structure could represent an
important transition phase between protoclusters and mature clusters. It provides evidence that the
main phase of massive galaxy passivization will take place after galaxies accrete onto the cluster,
providing new insights into massive cluster formation at early epochs. The large integrated stellar
mass at such high redshift challenges our understanding of massive cluster formation.
The characterization of_the_gamma_ray_signal_from_the_central_milk_way_a_comp...Sérgio Sacani
Past studies have identified a spatially extended excess of ∼1-3 GeV gamma rays from the region
surrounding the Galactic Center, consistent with the emission expected from annihilating dark
matter. We revisit and scrutinize this signal with the intention of further constraining its characteristics
and origin. By applying cuts to the Fermi event parameter CTBCORE, we suppress the tails
of the point spread function and generate high resolution gamma-ray maps, enabling us to more
easily separate the various gamma-ray components. Within these maps, we find the GeV excess
to be robust and highly statistically significant, with a spectrum, angular distribution, and overall
normalization that is in good agreement with that predicted by simple annihilating dark matter
models. For example, the signal is very well fit by a 36-51 GeV dark matter particle annihilating to
b
¯b with an annihilation cross section of σv = (1−3)×10−26 cm3
/s (normalized to a local dark matter
density of 0.4 GeV/cm3
). Furthermore, we confirm that the angular distribution of the excess is
approximately spherically symmetric and centered around the dynamical center of the Milky Way
(within ∼0.05◦
of Sgr A∗
), showing no sign of elongation along the Galactic Plane. The signal is
observed to extend to at least ' 10◦
from the Galactic Center, disfavoring the possibility that this
emission originates from millisecond pulsars.
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.
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.
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
Extensive Noachian fluvial systems in Arabia Terra: Implications for early Ma...Sérgio Sacani
Valley networks are some of the strongest lines of evidence for
extensive fluvial activity on early (Noachian; >3.7 Ga) Mars. However,
their purported absence on certain ancient terrains, such as
Arabia Terra, is at variance with patterns of precipitation as predicted
by “warm and wet” climate models. This disagreement has contributed
to the development of an alternative “icy highlands” scenario,
whereby valley networks were formed by the melting of highland ice
sheets. Here, we show through regional mapping that Arabia Terra
shows evidence for extensive networks of sinuous ridges. We interpret
these ridge features as inverted fluvial channels that formed in
the Noachian, before being subject to burial and exhumation. The
inverted channels developed on extensive aggrading flood plains. As
the inverted channels are both sourced in, and traverse across, Arabia
Terra, their formation is inconsistent with discrete, localized sources
of water, such as meltwater from highland ice sheets. Our results are
instead more consistent with an early Mars that supported widespread
precipitation and runoff.
Very regular high-frequency pulsation modes in young intermediate-mass starsSérgio Sacani
Asteroseismology probes the internal structures of stars by using their natural
pulsation frequencies1. It relies on identifying sequences of pulsation modes that can
be compared with theoretical models, which has been done successfully for many
classes of pulsators, including low-mass solar-type stars2, red giants3, high-mass stars4
and white dwarfs5. However, a large group of pulsating stars of intermediate mass—the
so-called δ Scuti stars—have rich pulsation spectra for which systematic mode
identification has not hitherto been possible6,7. This arises because only a seemingly
random subset of possible modes are excited and because rapid rotation tends to
spoil regular patterns8–10. Here we report the detection of remarkably regular
sequences of high-frequency pulsation modes in 60 intermediate-mass
main-sequence stars, which enables definitive mode identification. The space
motions of some of these stars indicate that they are members of known associations
of young stars, as confirmed by modelling of their pulsation spectra.
Measurement of Jupiter’s asymmetric gravity fieldSérgio Sacani
The gravity harmonics of a fluid, rotating planet can be decomposed
into static components arising from solid-body rotation and dynamic
components arising from flows. In the absence of internal dynamics,
the gravity field is axially and hemispherically symmetric and is
dominated by even zonal gravity harmonics J2n that are approximately
proportional to qn, where q is the ratio between centrifugal
acceleration and gravity at the planet’s equator1
. Any asymmetry in the
gravity field is attributed to differential rotation and deep atmospheric
flows. The odd harmonics, J3, J5, J7, J9 and higher, are a measure of the
depth of the winds in the different zones of the atmosphere2,3
. Here
we report measurements of Jupiter’s gravity harmonics (both even
and odd) through precise Doppler tracking of the Juno spacecraft
in its polar orbit around Jupiter. We find a north–south asymmetry,
which is a signature of atmospheric and interior flows. Analysis of
the harmonics, described in two accompanying papers4,5
, provides
the vertical profile of the winds and precise constraints for the depth
of Jupiter’s dynamical atmosphere.
Early optical spectra_of_nova_v1369_cen_show_the_presence_of_lithiumSérgio Sacani
O elemento químico lítio foi encontrado pela primeira vez em material ejetado por uma nova. Observações da Nova Centauri 2013 obtidas com o auxílio de telescópios no Observatório de La Silla do ESO e perto de Santiago do Chile, ajudaram a explicar por que é que muitas estrelas jovens parecem ter mais quantidade deste elemento químico do que o esperado. Esta nova descoberta acrescenta uma importante peça que faltava ao quebra-cabeças que representa a evolução química da nossa Galáxia e é um enorme passo em frente na compreensão das quantidades dos diferentes elementos químicos nas estrelas da Via Láctea.
O elemento químico leve lítio é um dos poucos elementos que se prevê ter sido criado pelo Big Bang, há 13,8 bilhões de anos atrás. No entanto, tentar compreender as quantidades de lítio observadas nas estrelas que nos rodeiam hoje tem sido um processo muito difícil. Estrelas mais velhas possuem menos lítio do que o esperado [1] e algumas estrelas jovens têm dez vezes mais lítio do que o que pensávamos [2].
Desde os anos 1970 que os astrônomos especulam que a enorme quantidade de lítio encontrado nas estrelas jovens poderá vir de novas — explosões estelares que libertam material para o espaço entre as estrelas, contribuindo assim para a matéria que forma a próxima geração de estrelas. No entanto, observações cuidadas de várias novas não tinham, até agora, fornecido resultados claros.
Uma equipe liderada por Luca Izzo (Universidade Sapienza de Roma e ICRANet, Pescara, Itália) utilizou o instrumento FEROS montado no telescópio MPG/ESO de 2,2 metros instalado no Observatório de La Silla, assim como o espectrógrafo PUCHEROS montado no telescópio de 0,5 metros do ESO, no Observatório da Pontificia Universidad Catolica de Chile em Santa Marina, perto de Santiago, para estudar a nova Nova Centauri 2013 (V1369 Centauri). Esta estrela explodiu no céu austral perto da estrela brilhante Beta Centauri em dezembro de 2013, tratando-se, até agora, da nova mais brilhante deste século — facilmente observada a olho nu [3].
The x ray_outburst_of_the_galactic_centre_magnetar_sgr_j1745_2900_during_the_...Sérgio Sacani
Artigo descreve a pesquisa feita com a magnetar localizada próxima do buraco negro supermassivo da Via Láctea e que tenta explicar o comportamento estranho e incomum desse objeto misterioso.
Artigo descreve a descoberta feita pelo Hubble de que duas luas de Plutão descrevem suas órbitas realizando cambalhotas imprevisíveis. Além disso, o estudo descobriu um link entre as órbitas das luas menores de Plutão.
The morphological diversity_of_comet_67_p_churyumov_gerasimenkoSérgio Sacani
Artigo descreve em detalhes as unidades morfológicas do cometa Churyumov-Gerasimenko, classificadas pelos cientistas com as análises feitas nas imagens de alta resolução da sonda Rosetta da ESA.
Artigo descreve estudo feito com o Hubble que mostra o elo entre os buracos negros que apresentam os poderosos jatos relativísticos e galáxias massivas em fusão.
The formation of_a_quadruple_star_system_with_wide_separationSérgio Sacani
Artigo da Nature que reporta a observação feita da formação de um sistema quadruplo de estrelas. Pela primeira vez, os estágios iniciais de formação desse tipo de sistema é observado.
Galaxy dynamics and the mass density of the universeSérgio Sacani
Dynamical evidence accumulated over the
past 20 years has convinced astronomers that luminous matter
in a spiral galaxy constitutes no more than 10% of the mass of
a galaxy. An additional 90% is inferred by its gravitational
effect on luminous material. Here I review recent observations
concerning the distribution of luminous and nonluminous
matter in the Milky Way, in galaxies, and in galaxy clusters.
Observations of neutral hydrogen disks, some extending in
radius several times the optical disk, confirm that a massive
dark halo is a major component of virtually every spiral. A
recent surprise has been the discovery that stellar and gas
motions in ellipticals are enormously complex. To date, only for
a few spheroidal galaxies do the velocities extend far enough to
probe the outer mass distribution. But the diverse kinematics
of inner cores, peripheral to deducing the overall mass distribution,
offer additional evidence that ellipticals have acquired
gas-rich systems after initial formation. Dynamical results are
consistent with a low-density universe, in which the required
dark matter could be baryonic. On smallest scales of galaxies
[10 kiloparsec (kpc); H. = 50 kmsec'lmegaparsec'11 the
luminous matter constitutes only 1% of the closure density. On
scales greater than binary galaxies (i.e., .100 kpc) all systems
indicate a density -10% of the closure density, a density
consistent with the low baryon density in the universe. If
large-scale motions in the universe require a higher mass
density, these motions would constitute the first dynamical
evidence for nonbaryonic matter in a universe of higher
density.
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Accepted to ApJ Letters on 30 January, 2013.
Preprint typeset using LATEX style emulateapj v. 5/2/11
THE MASS-RADIUS RELATION FOR 65 EXOPLANETS SMALLER THAN 4 EARTH RADII
Lauren M. Weiss
1,†
& Geoffrey W. Marcy
1
1B-20 Hearst Field Annex, Astronomy Department, University of California, Berkeley, CA 94720
Accepted to ApJ Letters on 30 January, 2013.
ABSTRACT
We study the masses and radii of 65 exoplanets smaller than 4R⊕ with orbital periods shorter
than 100 days. We calculate the weighted mean densities of planets in bins of 0.5 R⊕ and identify a
density maximum of 7.6 g cm−3at 1.4 R⊕. On average, planets with radii up to RP = 1.5R⊕ increase
in density with increasing radius. Above 1.5 R⊕, the average planet density rapidly decreases with
increasing radius, indicating that these planets have a large fraction of volatiles by volume overlying
a rocky core. Including the solar system terrestrial planets with the exoplanets below 1.5 R⊕, we
find ρP = 2.43 + 3.39 (RP/R⊕) g cm
−3 for RP < 1.5R⊕, which is consistent with rocky compositions.
For 1.5 ≤ RP/R⊕ < 4, we find MP/M⊕ = 2.69 (RP/R⊕)
0.93
. The RMS of planet masses to the fit
between 1.5 and 4 R⊕ is 4.3 M⊕ with reduced χ
2 = 6.2. The large scatter indicates a diversity in
planet composition at a given radius. The compositional diversity can be due to planets of a given
volume (as determined by their large H/He envelopes) containing rocky cores of different masses or
compositions.
1. INTRODUCTION
The Kepler Mission has found an abundance of planets
with radii RP < 4R⊕ (Batalha et al. 2013); the most re-
cent head-count indicates 3206 planet candidates in this
size range (NASA exoplanet Archive, queried 15 Jan.
2014), most of which are real (Morton & Johnson 2011).
Although there are no planets between the size of Earth
and Neptune in the solar system, occurrence calculations
that de-bias the orbital geometry and completeness of
the Kepler survey find that planets between the size of
Earth and Neptune are common in our galaxy, occurring
with orbital periods between 5 and 50 days around 24%
of stars (Petigura et al. 2013). However, in many sys-
tems, it is difficult to measure the masses of such small
planets because the gravitational acceleration these plan-
ets induce on their host stars or neighboring planets is
challenging to detect with current telescopes and instru-
ments. We cannot hope to measure the masses of all
planets in this size range discovered by Kepler. Ob-
taining measurements of the masses of a subset of these
planets and characterizing their compositions is vital to
understanding the formation and evolution of this pop-
ulation of planets.
Many authors have explored the relation between
planet mass and radius as a means for understanding
exoplanet compositions and as a predictive tool. Sea-
ger et al. (2007) predict the mass-radius relationship for
planets of various compositions. Th ...
Eccentricity from transit_photometry_small_planets_in_kepler_multi_planet_sys...Sérgio Sacani
Artigo descreve estudo que mostra que a órbita dos exoplanetas terrestres são na sua maioria órbitas circulares, o que é bom para se procurar por vida e o que vem causando uma revolução no entendimento sobre os sistemas de exoplanteas.
An Earth-sized exoplanet with a Mercury-like compositionSérgio Sacani
Earth, Venus, Mars and some extrasolar terrestrial planets1
have a mass and radius that is consistent with a mass fraction
of about 30% metallic core and 70% silicate mantle2
. At the
inner frontier of the Solar System, Mercury has a completely
different composition, with a mass fraction of about 70%
metallic core and 30% silicate mantle3
. Several formation or
evolution scenarios are proposed to explain this metal-rich
composition, such as a giant impact4, mantle evaporation5
or the depletion of silicate at the inner edge of the protoplanetary
disk6. These scenarios are still strongly debated.
Here, we report the discovery of a multiple transiting planetary
system (K2-229) in which the inner planet has a radius
of 1.165 ± 0.066 Earth radii and a mass of 2.59 ± 0.43 Earth
masses. This Earth-sized planet thus has a core-mass fraction
that is compatible with that of Mercury, although it was
expected to be similar to that of Earth based on host-star
chemistry7
. This larger Mercury analogue either formed with
a very peculiar composition or has evolved, for example, by
losing part of its mantle. Further characterization of Mercurylike
exoplanets such as K2-229 b will help to put the detailed
in situ observations of Mercury (with MESSENGER and
BepiColombo8) into the global context of the formation and
evolution of solar and extrasolar terrestrial planets.
Lunar ejecta origin of near-Earth asteroid Kamo’oalewa is compatible with rar...Sérgio Sacani
Near-Earth asteroid, Kamo’oalewa (469219), is one of a small number of known quasisatellites of Earth; it transitions between quasi-satellite and horseshoe orbital states on
centennial timescales, maintaining this dynamics over megayears. The similarity of its
reflectance spectrum to lunar silicates and its Earth-like orbit both suggest that it originated
from the lunar surface. Here we carry out numerical simulations of the dynamical evolution of
particles launched from different locations on the lunar surface with a range of ejection
velocities in order to assess the hypothesis that Kamo‘oalewa originated as a debris-fragment
from a meteoroidal impact with the lunar surface. As these ejecta escape the Earth-Moon
environment, they face a dynamical barrier for entry into Earth’s co-orbital space. However, a
small fraction of launch conditions yields outcomes that are compatible with Kamo‘oalewa’s
orbit. The most favored conditions are launch velocities slightly above the escape velocity
from the trailing lunar hemisphere.
Similar to The mass of_the_mars_sized_exoplanet_kepler_138_b_from_transit_timing (20)
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.
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.
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
Richard's entangled aventures in wonderlandRichard Gill
Since the loophole-free Bell experiments of 2020 and the Nobel prizes in physics of 2022, critics of Bell's work have retreated to the fortress of super-determinism. Now, super-determinism is a derogatory word - it just means "determinism". Palmer, Hance and Hossenfelder argue that quantum mechanics and determinism are not incompatible, using a sophisticated mathematical construction based on a subtle thinning of allowed states and measurements in quantum mechanics, such that what is left appears to make Bell's argument fail, without altering the empirical predictions of quantum mechanics. I think however that it is a smoke screen, and the slogan "lost in math" comes to my mind. I will discuss some other recent disproofs of Bell's theorem using the language of causality based on causal graphs. Causal thinking is also central to law and justice. I will mention surprising connections to my work on serial killer nurse cases, in particular the Dutch case of Lucia de Berk and the current UK case of Lucy Letby.
(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.
Richard's aventures in two entangled wonderlandsRichard Gill
Since the loophole-free Bell experiments of 2020 and the Nobel prizes in physics of 2022, critics of Bell's work have retreated to the fortress of super-determinism. Now, super-determinism is a derogatory word - it just means "determinism". Palmer, Hance and Hossenfelder argue that quantum mechanics and determinism are not incompatible, using a sophisticated mathematical construction based on a subtle thinning of allowed states and measurements in quantum mechanics, such that what is left appears to make Bell's argument fail, without altering the empirical predictions of quantum mechanics. I think however that it is a smoke screen, and the slogan "lost in math" comes to my mind. I will discuss some other recent disproofs of Bell's theorem using the language of causality based on causal graphs. Causal thinking is also central to law and justice. I will mention surprising connections to my work on serial killer nurse cases, in particular the Dutch case of Lucia de Berk and the current UK case of Lucy Letby.
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.
Cancer cell metabolism: special Reference to Lactate PathwayAADYARAJPANDEY1
Normal Cell Metabolism:
Cellular respiration describes the series of steps that cells use to break down sugar and other chemicals to get the energy we need to function.
Energy is stored in the bonds of glucose and when glucose is broken down, much of that energy is released.
Cell utilize energy in the form of ATP.
The first step of respiration is called glycolysis. In a series of steps, glycolysis breaks glucose into two smaller molecules - a chemical called pyruvate. A small amount of ATP is formed during this process.
Most healthy cells continue the breakdown in a second process, called the Kreb's cycle. The Kreb's cycle allows cells to “burn” the pyruvates made in glycolysis to get more ATP.
The last step in the breakdown of glucose is called oxidative phosphorylation (Ox-Phos).
It takes place in specialized cell structures called mitochondria. This process produces a large amount of ATP. Importantly, cells need oxygen to complete oxidative phosphorylation.
If a cell completes only glycolysis, only 2 molecules of ATP are made per glucose. However, if the cell completes the entire respiration process (glycolysis - Kreb's - oxidative phosphorylation), about 36 molecules of ATP are created, giving it much more energy to use.
IN CANCER CELL:
Unlike healthy cells that "burn" the entire molecule of sugar to capture a large amount of energy as ATP, cancer cells are wasteful.
Cancer cells only partially break down sugar molecules. They overuse the first step of respiration, glycolysis. They frequently do not complete the second step, oxidative phosphorylation.
This results in only 2 molecules of ATP per each glucose molecule instead of the 36 or so ATPs healthy cells gain. As a result, cancer cells need to use a lot more sugar molecules to get enough energy to survive.
Unlike healthy cells that "burn" the entire molecule of sugar to capture a large amount of energy as ATP, cancer cells are wasteful.
Cancer cells only partially break down sugar molecules. They overuse the first step of respiration, glycolysis. They frequently do not complete the second step, oxidative phosphorylation.
This results in only 2 molecules of ATP per each glucose molecule instead of the 36 or so ATPs healthy cells gain. As a result, cancer cells need to use a lot more sugar molecules to get enough energy to survive.
introduction to WARBERG PHENOMENA:
WARBURG EFFECT Usually, cancer cells are highly glycolytic (glucose addiction) and take up more glucose than do normal cells from outside.
Otto Heinrich Warburg (; 8 October 1883 – 1 August 1970) In 1931 was awarded the Nobel Prize in Physiology for his "discovery of the nature and mode of action of the respiratory enzyme.
WARNBURG EFFECT : cancer cells under aerobic (well-oxygenated) conditions to metabolize glucose to lactate (aerobic glycolysis) is known as the Warburg effect. Warburg made the observation that tumor slices consume glucose and secrete lactate at a higher rate than normal tissues.
Professional air quality monitoring systems provide immediate, on-site data for analysis, compliance, and decision-making.
Monitor common gases, weather parameters, particulates.
The mass of_the_mars_sized_exoplanet_kepler_138_b_from_transit_timing
1. LETTER doi:10.1038/nature14494
The mass of the Mars-sized exoplanet Kepler-138 b
from transit timing
Daniel Jontof-Hutter1,2
, Jason F. Rowe2,3
, Jack J. Lissauer2
, Daniel C. Fabrycky4
& Eric B. Ford1
Extrasolar planets that pass in front of their host star (transit)
cause a temporary decrease in the apparent brightness of the star,
providing a direct measure of the planet’s size and orbital period.
In some systems with multiple transiting planets, the times of the
transits are measurably affected by the gravitational interactions
between neighbouring planets1,2
. In favourable cases, the depar-
tures from Keplerian orbits (that is, unaffected by gravitational
effects) implied by the observed transit times permit the planetary
masses to be measured, which is key to determining their bulk
densities3
. Characterizing rocky planets is particularly difficult,
because they are generally smaller and less massive than gaseous
planets. Therefore, few exoplanets near the size of Earth have had
their masses measured. Here we report the sizes and masses of three
planets orbiting Kepler-138, a star much fainter and cooler than
the Sun. We determine that the mass of the Mars-sized inner pla-
net, Kepler-138 b, is 0:066z0:059
{0:037 Earth masses. Its density is 2:6z2:4
{1:5
grams per cubic centimetre. The middle and outer planets are both
slightly larger than Earth. The middle planet’s density (6:2z5:8
{3:4
grams per cubic centimetre) is similar to that of Earth, and the
outer planet is less than half as dense at 2:1z2:2
{1:2 grams per cubic
centimetre, implying that it contains a greater portion of low-
density components such as water and hydrogen.
NASA’s Kepler mission has discovered thousands of candidate
transiting exoplanets, with a wide range of planetary sizes4–6
. A small
fraction of these planets have had their masses characterized, either by
radial-velocity spectroscopy or by transit timing. The latter probes the
gravitational perturbations between planets in multi-planet systems by
precisely measuring transit times and fitting dynamical models to the
observed transit timing variations (TTV)1,2
. Both radial velocity and
TTV signals are larger for more massive planets and improve with
greaterplanetary masses,although the twotechniques sampledifferent
populations of exoplanets. The radial-velocity technique measures the
motion of a host star induced by its planet’s gravity, and hence the
signal declines with increasing orbital distance.
The majority of mass measurements of planets discovered in the
Kepler dataset have been the results of radial velocity observations. For
Kepler-discovered planets characterized as rocky by this method, the
orbital periods are all less than a few days. Of the radial-velocity detec-
tions, Kepler-78 b has the lowest mass (1.7M›, where M› is the
Earth’s mass), and the shortest orbital period (0.35 days)7,8
.
Characterizing planets by transit timing is quite complementary to
using radial velocity because transit timing is very sensitive to pertur-
bations between planets that are closely spaced or near orbital reso-
nances3,9
. We note that most systems with detected TTVs are not in
resonance, but rather are near enough to resonance for the perturba-
tions to be coherent for many orbital periods, while also far enough
from resonance that the planetary conjunctions cycle around the orbit
plane within the four-year Kepler baseline. For near-resonant pairs,
the TTVs of neighbouring planets frequently take the form of anti-
correlated sinusoids over many orbits10–14
or the sum of sinusoids
where a planet is perturbed by two neighbours15
. The majority of
TTV detections have been found near first-order mean-motion
resonances, such that planet pairs have an orbital period ratio near
to j:j 21, where j is an integer. Near first-order resonances generally
cause stronger TTV signals than second-order resonances, although
much depends on how close the planet pairs are to resonance and how
eccentric (non-circular) their orbits are, as well as the masses of the
planets. Eccentricity causes the orbital speed to vary during the orbit,
and the distance between the planets at conjunction to vary with the
position of the conjunction.
The bulk of planets with mass characterizations from the Kepler
sample using TTVs so far have orbital periods ranging from about 10
days to 100 days. These generally have low density15–18
and probably
possess deep atmospheres, with the exception of the rocky planet
Kepler-36 b19
.
Kepler-138 (formerly known as KOI-314) hosts three validated
transiting planets20
. The orbital periods of Kepler-138’s three planets
are given in Table 1. Kepler-138 c and Kepler-138 d orbit near a
1
Department of Astronomy, Pennsylvania State University, Davey Laboratory, University Park, Pennsylvania 16802, USA. 2
NASA Ames Research Center, Moffett Field, California 94035, USA. 3
SETI Institute,
189 North Bernardo Avenue, Mountain View, California 94043, USA. 4
Department of Astronomy and Astrophysics, University of Chicago, 5640 South Ellis Avenue, Chicago, Illinois 60637, USA.
1 8 J U N E 2 0 1 5 | V O L 5 2 2 | N A T U R E | 3 2 1
Table 1 | Stellar and planetary parameters for the Kepler-138 system
Adopted stellar parameters
Stellar mass, Mw Stellar radius, Rw Effective temperature, Teff Stellar density, rw Metallicity, [Fe/H] log[g (cm s22
)]
(0.521 6 0.055)M[ (0.442 6 0.024)R[ 3,841 6 49 K 9.5 6 2.2 g cm23
20.280 6 0.099 4.886 6 0.055
Dynamical modelling parameters
Planet Period (days) T0 (BJD 2 2,454,900) ecosv esinv (Mp/M›) 3 (M[/Mw)
b 10.3126z0:0004
{0:0006 788.4142z0:0027
{0:0027 20.011z0:096
{0:140 20.024z0:075
{0:135 0.13z0:12
{0:08
c 13.7813z0:0001
{0:0001 786.1289z0:0005
{0:0005 20.015z0:086
{0:126 20.020z0:064
{0:117 3.85z3:77
{2:30
d 23.0881z0:0009
{0:0008 796.6689z0:0013
{0:0013 20.037z0:060
{0:092 20.057z0:674
{0:387 1.28z1:36
{0:78
Adopted physical characteristics
Planet Rp/Rw Mp (M›) Rp (R›) Density (g cm23
) Incident flux relative to Earth
b 0.0108z0:0003
{0:0003 0.066z0:059
{0:037 0.522z0:032
{0:032 2.6z2:4
{1:5 6.81z0:84
{0:84
c 0.0247z0:0005
{0:0005 1.970z1:912
{1:120 1.197z0:070
{0:070 6.2z5:8
{3:4 4.63z0:57
{0:57
d 0.0251z0:0007
{0:0007 0.640z0:674
{0:387 1.212z0:075
{0:075 2.1z2:2
{1:2 2.32z0:29
{0:29
G2015 Macmillan Publishers Limited. All rights reserved
2. second-order mean-motion resonance (5:3), while Kepler-138 b and
Kepler-138 c orbit near the 4:3 first-order resonance.
Using transit times up to the fourteenth quarter of the Kepler mis-
sion, two of the three known planets orbiting Kepler-13820
have been
confirmed and characterized with TTVs21
. The derived parameters in
that work suggested that the outer planet, Kepler-138 d, has a density
so low that it must have a substantial hydrogen/helium gaseous
envelope21
.
Using the complete Kepler data set for Kepler-138, we have detected
TTVs for all three planets (see Fig. 1). We describe our procedure for
measuring transit times in the Methods, and list our transit time mea-
surements in Extended Data Table 1. TTVs are expressed as the dif-
ference between the observed transit times and the calculated linear fit
to the transit times. Modelling Kepler-138 as a three-planet system, we
measure the masses of all three planets, the super-Earth-sized Kepler-
138 c and Kepler-138 d, as well as Kepler-138 b, which at 0.52R› is
roughly the size of Mars.
We performed dynamical fits by calculating the orbits of the three
planets around the star. We modelled the orbits as being co-planar,
given that all three planets are transiting, that Kepler’s multi-planet
systems are known to have small mutual inclinations, and that we
demonstrate that allowing mutual inclinations has little effect on our
results for the planet masses (see Extended Data Fig. 7c).
Our model parameters for each planet are the orbital period P, the
time T0 of the first transit after our chosen epoch, the components of
the eccentricity vector (ecosv and esinv, where v is the angle between
the sky plane and the orbital pericentre of the planet), and Mp/Mw, the
mass of the planet relative to the host star, which we express as (Mp/
M›)(M[/Mw) throughout, where M[ is the mass of the Sun. We
perform Bayesian parameter estimation for these 15 model parameters
using differential evolution Markov Chain Monte Carlo analysis. We
report the properties of the star and planets in Table 1, and details of
the parameter estimation algorithm, priors and statistical models in
the Methods.
We measure the mass of Kepler-138 b to be 0:066z0:059
{0:037M›, where
uncertainties denote the 68.3% confidence limits. The 95.4% interval
spans 0.011M› to 0.170M›. The robustness of this result against
outlying transit times and mutual inclinations is demonstrated in
the Methods.
The posterior probability for the inner planet having non-zero mass
is between 99.82% and 99.91% (depending on the choice of prior for
eccentricity e), that is, equivalent to a 3s detection. This calculation is
based on the Savage–Dickey density ratio for calculating the Bayes
factor, which fully accounts for posterior width and shape, including
asymmetries and non-Gaussianity, as described in Methods.
Kepler-138 b is by far the smallest exoplanet, both by radius and
mass, to have a density measurement (see Fig. 2). Thus it opens up a
new regime to physical study. It is likely to become the prototype for a
class of small close-in planets that could be common. The prospect of
further constraints on this planet are excellent, because NASA’s
Transiting Exoplanet Survey Satellite should be able to measure transit
times for the two largest planets, improving constraints on the dynam-
ical model for all three planets. The European Space Agency’s Plato
mission will continue this process and ground-based measurements
may also be possible. These future observations, plus more accurate
stellar classification using the distance to the star measured by the
European Space Agency’s Gaia mission, will further improve the char-
acterization of this system, especially the inner planet.
Our measurements of the mass and density of the small inner planet
Kepler-138 b are consistent with various compositions and formation
locations. If future observations imply that the planet is less dense than
rock, then the only physically and cosmogonically plausible low-
density constituents are water and other astrophysical ices, which
could only have condensed far from the star. That would be the first
definitive evidence for substantial inward orbital migration of a small
planet.
For the two outer planets, Kepler-138 c and Kepler-138 d, we find a
lower mass ratio between these two planets than does previous work21
.
This is not surprising, since Kepler-138 b’s perturbations explain part
of the TTVs observed in Kepler-138 c, which were previously attrib-
uted solely to perturbations by Kepler-138 d. Nevertheless, the mass
ratios between each of these planets and their host star remains con-
sistent with published results21
. We find higher densities for both of
these planets than does previous work, owing to our improved stellar
–100
–50
0
50
100
150
0 400 800 1,200 1,600 0 400 800 1,200 1,600 0 400 800 1,200 1,600
15 30
20
10
0
–10
–20
–30
10
5
0
–5
–10
–15
–20
BJD – 2,454,900
Kepler-138 b Kepler-138 c Kepler-138 d
a
TTV(min)
b c
BJD – 2,454,900 BJD – 2,454,900
Figure 1 | Transit timing variations of the three planets orbiting Kepler-
138. In black are the differences between measured transit times and a
calculated linear fit to the transit times, with 1s uncertainties shown as error
bars. Grey points mark the difference between the simulated transit times based
on the best-fit dynamical model and a linear fit to the transit times. a, TTV of
Kepler-138 b; b, TTV of Kepler-138 c; c, TTV of Kepler-138 d.
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
0.01 0.1 1 10
Rp/R⊕
Mp/M⊕
1
g
cm–3
3 g cm
–3
10 g cm
–3
Earth
Venus
Mercury
Mars
Figure 2 | Mass–radius diagram of well characterized planets smaller than
2.1 Earth radii, R›. Prior exoplanet characterizations and 1s uncertainties are
shown as grey points7–9,15,16,19,25–30
. Black points from left to right are Mercury,
Mars, Venus and Earth. Red data points are our results for Kepler-138.
Open circles mark previously measured masses for Kepler-138 c and Kepler-138
d21
. Error bars mark published 1s uncertainties for the planets of Kepler-138
and masses and radii of all other characterized exoplanets within this size
range. The curves mark bulk densities of 1 g cm23
, 3 g cm23
and 10 g cm23
.
3 2 2 | N A T U R E | V O L 5 2 2 | 1 8 J U N E 2 0 1 5
RESEARCH LETTER
G2015 Macmillan Publishers Limited. All rights reserved
3. properties, particularly the higher stellar density and consequent smal-
ler stellar radius.
Previous estimates of the size and mass of the outer planet Kepler-
138 d implied that the planet possessed a hydrogen-rich atmosphere21
,
which is difficult to explain with our current understanding of the
accretion and retention of light gases from low-mass planets orbiting
close to their star22–24
. Our new measurements could be explained by a
composition of rock and water. A planet made of rock and water would
be more stable against mass loss, and would imply that the planet
formed at a greater distance from the star and migrated.
Online Content Methods, along with any additional Extended Data display items
andSource Data, are available in the onlineversion of the paper; references unique
to these sections appear only in the online paper.
Received 9 September 2014; accepted 17 April 2015.
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Acknowledgements D.J-H. acknowledges support through the NASA Postdoctoral
Program and funding fromthe Center for Exoplanets and Habitable Worlds. The Center
for Exoplanets and Habitable Worldsissupported bythe PennsylvaniaStateUniversity,
the Eberly College of Science and the Pennsylvania Space Grant Consortium. J.F.R.
acknowledges NASA grant NNX14AB92G issued through the Kepler Participating
Scientist Program. D.C.F. is an Alfred P. Sloane Fellow and was supported by the Kepler
Participating Scientist Program award NNX14AB87G. E.B.F. was supported in part by
NASA Kepler Participating Scientist Program award NNX14AN76G and NASA
ExoplanetResearchProgramawardNNX15AE21G,aswellasthe Centerfor Exoplanets
and Habitable Worlds.
Author Contributions D.J.-H. led the research effort to model the TTV, constrain
planetary masses, and wrote the manuscript. J.F.R. measured transit times from the
Kepler data set, characterized the host star using spectral follow-up of the target and
constraints from the transits and edited the manuscript. J.J.L. led the interpretation
effort, assisted in the dynamical study and writing the manuscript. D.C.F. wrote the
software to simulate planetary transits, assisted in interpreting results and edited the
manuscript. E.B.F. assisted in the development of statistical methodologies and
robustness tests for the TTV modelling and edited the manuscript.
Author Information Reprints and permissions information is available at
www.nature.com/reprints. The authors declare no competing financial interests.
Readers are welcome to comment on the online version of the paper. Correspondence
and requests for materials should be addressed to D.J.-H. (dxj14@psu.edu).
1 8 J U N E 2 0 1 5 | V O L 5 2 2 | N A T U R E | 3 2 3
LETTER RESEARCH
G2015 Macmillan Publishers Limited. All rights reserved
4. METHODS
We have used all available short-cadence Kepler data and long-cadence data
wherever short-cadence data are unavailable to complete the data set for 17 quar-
ters. We list the transit times for each planet in Extended Data Table 1.
Throughout, we express times since Barycentric Julian Day (BJD) minus 2,454,900.
Photometric transit and stellar models. From the light curve, we filtered instru-
mental and astrophysical effects that are independent of planetary transits. To
each segment of the photometric time series, we fitted a cubic polynomial of width
2 days, centred on the time of each measurement20
. We excluded measurements
taken within one transit duration (defined as the time from first to last contact) of
the measured centre of the transit and extrapolate the polynomial to estimate
corrections during transits. This process strongly filters astrophysical signals with
timescales of approximately 2 days, which could affect the shape of a planetary
transit.We also excluded measurementsfor which the associated segmenthas gaps
longer than 2.5 h.
We fitted the detrended Kepler light curve using a transit model for quadratic
limb-darkening31
and non-circular Keplerian orbits. We stacked transits of each
planet with corrections for the measured TTVs20
. To account for Kepler’s obser-
vation cadence, we averaged our transit model with 11 equal spacings within the
1 min or 30 min integration window. We evaluated the photometric noise for each
quarter of data to fit transit models, adopting published stellar parameters for
Kepler-13832
. We adopted a two-parameter quadratic model for limb-darkening
with fixed coefficients (0.3576, 0.3487) appropriate for Kepler’s bandpass and
Kepler-138’s effective temperature (Teff), log[g] and metallicity [Fe/H]33
.
The light curve model parameters consist of the mean stellar density34
rw, a
photometric zero pointforeachlightcurve segment, and foreachplanettheorbital
period, time of transit, planet-to-star radius ratio, impact parameter, and eccent-
ricity parameterized as ecosv and esinv. We determined posterior distributions of
ourmodel parameters using Markov Chain Monte Carlo techniques20
. Our best-fit
transit models, shown in Extended Data Fig. 1, resulted in consistent estimates for
rw from each planet.
We determined the mass and radius of Kepler-138 by fitting the spectroscopic
parameters (Teff, [Fe/H])32
and our light curve contraints of rw to Dartmouth
Stellar Evolution models35
, assuming a Gaussian probability density for each para-
meter32
. For the Dartmouth models, we varied initial conditions of mass, age, and
[Fe/H] and interpolated over a grid to evaluate Teff, rw, and [Fe/H] for any set of
initial conditions. We computed posteriors using Markov Chain Monte Carlo
analysis to obtain stellar model-dependent posteriors on Mw and Rw. Table 1 lists
our adopted stellar parameters. We tested the effects of eccentricity priors on our
measurement of rw, adopting a uniform prior in eccentricity as our nominal
results. We compare results with eccentricity fixed at zero in Extended Data
Fig. 2. Although a uniform prior on eccentricity results in a slightly wider range
of inferred radii for the star, both of these models are consistent with the spectro-
scopic study of Kepler-13832
.
Our solution for the impact parameter of the middle planet is 0.3 6 0.2, much
lower than the previous estimate of 0.92 6 0.0221
. The apparent U-shaped
transit for Kepler-138 c (Extended Data Fig. 1) is consistent with a low impact
parameter. Our measured impact parameter for Kepler-138 d is 0.810 6 0.057,
consistent with the previous measurement21
. Our revised impact parameters imply
rw 5 9.0 6 1.9 g cm23
, which agrees with our transit models for each planet, and
with the spectroscopic study of Kepler-13832
.
We find that Kepler-138 has a smaller mass and radius than previous estimates
based on the absolute K-band magnitude (MK) of the star from high-resolution
Keck spectra36
. These relied on mass–luminosity relations37
and a mass–radius
relation from interferometry38
. However, the calibration stars used to correlate the
MK to spectral index excluded cool stars that are active. In the case of Kepler-138,
the photometric time-series exhibits large (1%) variations due to starspots. These
increase the risk of systematic errors in the measurement of stellar luminosity, and
therefore the stellar properties derived from the mass–luminosity relation.
The time-scale for star-spot modulation, ,20 days, was much longer than the
transit duration, and was probably dominated by two spots. We found no evidence
of starspot crossings, nor did we find any TTV periodicities related to the rotation
period of the star. Hence, the stellar activity is unlikely to affect our transit model
or transit times.
Analytical constraints from TTV. Orbital period ratios determine how close
planets are to mean motion resonance, and over what period TTVs are expected
to cycle. The inner pair of planets of Kepler-138 orbit near the 4:3 resonance with an
expected TTV cycle of 1,570 days, slightly longer than the 1,454-day observational
baseline of Kepler-138 b’s transits. We fitted a sinusoid at this periodicity to the
TTVsoftheinnerplanet, anddetectedaTTVamplitudeof3464min.Thispermits
a rough estimate for the mass13
of the middle planet of (6.8 6 0.9)M›(M[/Mw),
which is close to our final measure of the mass of the middle planet.
The detection of TTVs at Kepler-138 b imply that the TTVs in Kepler-138 c
have a component caused by Kepler-138 b. However, the middle planet’s TTVs are
the combined effect of perturbations from its two neighbours Kepler-138 b and
Kepler-138 d, andtheouter pair orbitnear a second-ordermean motion resonance
for which there is no known analytical model. Hence, the masses of the inner and
outermost planets cannot be estimated by fitting such a simplified sinusoidal
model to the TTVs.
Detailed TTV modelling. For each set of initial conditions, we calculate the
transit times of all three planets based on Newtonian gravity, using an eighth-
order Dormand–Prince Runge–Kutta integrator15,16,39
. We compare the simulated
and observed transit times for each planet assuming each observed transit time has
an independent Gaussian measurement uncertainty.
We found an excess of outlying transit times to our model, where either instru-
mental effects or stellar activity led to a few unlikely transit times with under-
estimateduncertainties. Extended Data Fig. 3 shows the distribution of residualsto
our best-fit TTV model compared to a Gaussian distribution, revealing these
outliers. Of the 257 measured transit times, five are outliers, where for simulated
transittimes S, andmeasurementuncertainties sTT, (O 2S)/sTT . 3.Weremoved
these outliers, and used the 252 remaining measurements as our nominal data set
for dynamical models. Later, we tested our results for robustness against outliers.
Performing extensive grid searches and Levenberg–Marquardt analysis, we
found a single region of high posterior probability including multiple closely
related local minima. To characterize the masses and orbital parameters of the
three planets, we performed Bayesian parameter estimation using a differential
evolution Markov Chain Monte Carlo algorithm40,41
. We used Metropolis–
Hasting acceptance rules on 45 ‘walkers’ exploring parameter space in parallel,
where for each walker, a proposal is a scaled vector between two other walkers
chosen at random. Using differential evolution for the proposal steps increases the
probability that proposals will be accepted, particularly for target distributions
with strong correlations between model parameters.
The walkers were launched near the best-fit model found by Levenberg–
Marquardt analysis. We updated the vector scale length factor every 15 genera-
tions to keep the acceptance rate near the optimum value of 0.2540–42
and thinned
the data by recording every 20th generation in the Markov Chain. We discarded
the first 50,000 generations and continued the Markov Chain for 1,250,000 addi-
tional generations.
The mean correlation between parameter values in the same Markov Chain
Monte Carlo chain for a given separation in the chain begins near unity for
consecutive generations, and declines for greater separations43
. We used this
property to assess how well-mixed our Markov Chain Monte Carlo chains were.
The autocorrelation length, defined as the lag between generations required for the
correlation to fall below 0.5, varied between the walkers, averaging 9,000 genera-
tions for the planet-to-star mass ratio of Kepler-138 b. Hence, the mean length of
the differential evolution Markov Chain Monte Carlo chains was about 139 auto-
correlation lengths.
For each planet, we adopted a uniform prior in orbital period, T0, e, and v. For
Mp/Mw, we adopted a uniform prior that allowed negative masses to enable a
simple estimate for the significance of a positive mass for Kepler-138 b from the
posterior samples30
. For Kepler-138 b, the mass is greater than zero in 99.84% of
posterior samples. As a further test, we considered an alternative, more realistic,
uniform prior where planetary masses are positive definite and limited to the mass
of a pure iron planet (given their sizes)44,45
.
Posteriors for the mass ratios of each planet to the host star, and each eccent-
ricity vector component are shown in Extended Data Fig. 4. We list 68.3%, 95.4%,
and 99.7% credible intervals for all parameters in Extended Data Table 2. We also
include the mass ratios between the planets and relative eccentricity vector com-
ponents, which are more constrained by the data than absolute masses and eccent-
ricities.
Orbital eccentricity. Joint posteriors for the eccentricity vector components are
displayed in Extended Data Fig. 5. These show extreme correlations because a
broad class of orbital parameters in which there is a precise apsidal alignment of
orbits satisfies the data.
We performedlong-termintegrations on a subsetofourposterior planetmasses
and orbital parameters including a wide range of eccentricities using the HNBODY
code46
. We investigated whether long-term stability could further constrain the
eccentricities. A sample of the solutions were integrated for ten million orbits and
all were found to be stable. Integrating one of the best-fit solutions with high
eccentricities for Kepler-138 b, Kepler-138 c and Kepler-138 d of 0.23, 0.20 and
0.18 respectively, we confirmed that the orbits were stable for over one billion
years; the apsidal lock was maintained with the periapses of all three planets closely
aligned. Although rare in the Solar System, apsidal alignment has been observed
andstudied in the Uranian ring system47,48
andithasbeen detected in exoplanetary
systems, including u Andromedae49
, GJ 87650
and possibly 55 Cancri51
.
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5. Significance of mass detection for Kepler-138 b. We establish the statistical
significance of a non-zero mass for Kepler-138 b by computing the Bayes factor,
that is,theratio of the marginalized posterior probability fora model with the mass
of planet Kepler-138 b fixed at zero relative to the marginalized posterior prob-
ability for a model where all three planets have a non-zero mass. Intuitively, the
Bayes factor quantifies how much the transit timing data has increased our con-
fidence that Kepler-138 b has a non-zero mass. When performing Bayesian model
selection, it is essential to choose proper (that is, normalized) priors for any
parameters not occurring in both models. For the mass of Kepler-138 b we adopt
a uniform prior ranging between zero mass and the mass of an iron sphere the size
of Kepler-138 b. We tested two models of iron planets as upper limits on our mass
priors44,45
. We compute the Bayes factor using the generalized Savage–Dickey
density ratio based on the posterior samples from our nominal model52
. We find
that the three-massive-planets model is strongly favoured, with the posterior
probability for the three-massive-planets model equal to 99.82%44
(99.80%45
) for
our nominal model (that is, three massive planets, each with a uniform eccentricity
prior) or 99.91%44
(99.90%45
) for a model with three massive planets, each with a
Rayleigh distribution(s 5 0.0253
) for an eccentricity prior.A more restrictive prior
for the mass of Kepler-138 b would further increase the posterior probability for
the three-massive-planets model.
The generalized Savage–Dickey density ratio is superior to more commonly
used substitutes (such as the Akaike information criterion, AIC, or the Bayesian
Information Criterion, BIC), since the Savage–Dickey density ratio provides a
practical means of calculating the Bayes factor, the actual quantity of interest for
rigorous Bayesian model comparison. The AIC and BIC use only the likelihood of
the two best-fit models and do not account for the width or shape of the posterior
probability distributions. Extended Data Fig. 4a shows that the marginal posterior
for the mass of Kepler-138 b is asymmetric and non-Gaussian, so the AIC or BIC
would be a particularly poor choice for our problem.
Therefore, we have computed the rigorously correct Bayes factor using the
Savage–Dickey density ratio, which provides an efficient way of calculating the
Bayes factor when comparing two nested models, meaning that the simpler model
is equivalent to the more general model when the additional parameters (h) take
on a particular value (h 5 h0). In our case, this occurs when Mb 5 0. One
advantage of the Savage–Dickey density ratio over computing fully marginalized
likelihoods is that the Savage–Dickey density ratio can be computed from the
posterior for the more general model. This is computationally practical when
comparing models that differ by one to a few dimensions, since then the posterior
at h0 can be computed from a posterior sample using a kernel density estimator.
We estimate the posterior density using a Gaussian kernel density estimator with
bandwidth 0.001M›(Mw/M[), which was found to be optimal when analysing
synthetic posterior samples data. We verified that the results were insensitive to
varying the choice of bandwidth by an order of magnitude.
Sensitivity analyses. We performed several tests to assess the robustness of our
results to: (1) the choice of prior for eccentricity, (2) the treatment of transit time
outliers, (3) the assumption of co-planarity, and (4) our algorithm. For these
sensitivity analyses, we adopt our nominal prior for planet masses to allow for
negative planet masses. While any such models are clearly unphysical, allowing for
such models offers an efficient and intuitive means for evaluating whether the
lower limit on the planet masses is robust to the above assumptions.
Choice of eccentricity prior. As noted above, our nominal model has a uniform
prior in eccentricity. The joint posterior for the mass ratio of Kepler-138 b to the
host star and its orbital eccentricity is shown in Extended Data Fig. 5. We show this
plot with two alternative priors in eccentricity: a Rayleigh distribution with a scale
length 0.154
, and a more constrained one, consistent with Kepler’s multi-planet
systems, with a scale length of 0.0253
. Since the data constrain the eccentricity so
weakly, the choice of priors strongly affects the posteriors of eccentricity. However,
the planet-to-star mass ratios were much more weakly affected by the choice of
eccentricity prior, as shown in Extended Data Fig. 7a.
Because the apsidally locked solutions are long-term stable, we adopt the uniform
prior as our nominal solution, and note that a more constraining prior on eccent-
ricity results in a marginally wider posterior for mass ratio of Kepler-138 b to the
star. Although, as noted above, the orbital eccentricities in the system are only
weakly constrained, the relative eccentricities and mass ratios between the planets
are tightly constrained by the TTVs, as shown in Extended Data Fig. 6 and
Extended Data Table 2.
Transit time observation outliers. To assess the effect of residual outlying transit
times, we repeated the analysis with two other sets of measured transit times,
differing only in that we removed transit time residual outliers beyond (1) 4s
(leaving 254 transit times) or (2) 2.5s (leaving 244 transit times), as opposed to
our nominal data set, which excluded 3s outliers. Extended Data Fig. 3 shows the
relative frequency ofresidualscompared toa Gaussian. Themajority ofoutliers are
between 2.5s and 3s. We excluded outliers beyond 4s from all models.
The posterior for the mass of Kepler-138 b for each of these three data sets is
displayed for comparison in Extended Data Fig. 7b. Overall, the outliers have a
modest effect on the measured mass ratio for Kepler-138 b to the host star. Since
most of the outliersarein the transit times ofKepler-138 b,thesehave a smalleffect
on our mass measurement of Kepler-138 b. Furthermore, the mass of Kepler-138 c
is constrained by its effect on the transit times of both planets Kepler-138 b and
Kepler-138 d. Nevertheless, we note that the inclusion of more outliers increases
the skewness of the posterior for planetary mass and causes the mode of the
distribution to shift to a slightly lower mass.
Assumption of co-planarity. The known low inclination dispersion amongst
Kepler’s multiplanet systems makes co-planarity a reasonable assumption for
TTV modelling13,55,56
. Furthermore, geometric considerations make multi-planet
transiting less likely to be observed for systems with large mutual inclinations.
Nevertheless, we tested the effect of mutual inclinations on our solutions. We
performed two additional sets of simulations: (1) with the longitude of the ascend-
ing node of Kepler-138 b as a free parameter, leaving the other two planets as co-
planar, and (2) with a free ascending node for Kepler-138 d. In each case, we
adopted a uniform prior for the ascending node. In Extended Data Fig. 7c, we
compare the posteriors for the mass ratio of Kepler-138 b to the host star with
mutual inclinations to our nominal result. The nominal result gives a consistent,
but slightly wider posterior than with free ascending nodes.
Tests with synthetic transit times. We evaluated our method by generating
synthetic data sets of transit times with known planetary masses and orbital
parameters to test how well the input parameters were recovered. The results
are shown in Extended Data Fig. 8. We generated synthetic transit times based
on the median values of each parameter from the marginal posteriors of our
nominal model and added Gaussian noise to each observation with a standard
deviation equal to the measured timing uncertainties. Our analysis of the simu-
lated data results in a posterior for the mass of Kepler-138 b consistent with the
true values. While the resulting posterior for the mass of Kepler-138 b shows a
slightly higher mode and is less skewed than the posterior for the nominal model,
the differences are comparable to the minor effects of transit timing outliers or
choice of eccentricity prior. This result validates our both our transit timing
method and our TTV analysis.
Additionally, we generated eight independent synthetic data sets with zero mass
for Kepler-138 b and other parameters based on our nominal model (Extended
Data Fig. 8).In all eight cases, the posterior probability for Kepler-138 b’s mass was
insignificant, with only 16% to 86% of posterior samples having a mass greater
than zero, consistent with expectations for non-detections. This is in sharp con-
trast to our analysis of the actual data, which results in 99.84% of the posterior
yielding a positive mass for Kepler-138 b.
Planetary characteristics. Our adopted credible intervals in planetary mass and
density were calculated by repeatedly multiplying samples from the posteriors of
planet-to-star mass ratios, and Mw. Uncertainties in planetary radii were calcu-
lated with the fractional uncertainty in the stellar radius and the uncertainty in
planet-to-star radius ratio added in quadrature. Time-averaged incident flux for
each planet compared to the Earth was calculated in the low eccentricity limit,
although we note that if the orbits were highly eccentric, the fluxes would be
marginally higher.
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7. Extended Data Figure 1 | Folded light curves with corrections for observed
TTV for Kepler-138. The scattered points are photometric relative fluxes and
the curves are analytical models of the transit shape described in the text.
a, Kepler-138 b; b, Kepler-138 c; c, Kepler-138 d.
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8. Extended Data Figure 2 | Stellar mass and radius models using constraints
on the stellar mean density inferred from the light curve. In cyan are models
that adopted a uniform prior in eccentricity, and in magenta are constraints
found with orbital eccentricities fixed at zero. Grey points with error bars mark
stellar parameters found in the literature while the black error bars mark our
adopted solution for stellar mass and radius.
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9. Extended Data Figure 3 | The distribution of residual normalized
deviations from our best fit dynamical model to the raw transit times. The
histogram marks deviations calculated as: (O 2 S)/sTT, where O is the observed
transit time, S is the simulated transit time and sTT is the measurement
uncertainty. The green curve marks a Gaussian distribution.
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10. Extended Data Figure 4 | Posterior distributions for TTV model
parameters. Data are shown forour nominalmodel. a, The planet-to-star mass
ratio (Mp/Mw) for Kepler-138 b; b, Mp/Mw for Kepler-138 c; c, Mp/Mw for
Kepler-138 d. d, ecosv for Kepler-138 b; e, ecosv for Kepler-138 c; f, ecosv for
Kepler-138 d. g, esinv for Kepler-138 b; h, esinv for Kepler-138 c; i, esinv for
Kepler-138 d. The relative frequency for each histogram is scaled to the mode.
Mass ratios are scaled to the M[/M› mass ratio.
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11. Extended Data Figure 5 | Joint posteriors of model parameters and the
effects of eccentricity priors. The dark (light) grey marks the 68.3% (95.4%)
credible intervals for each joint posterior. a–c, Mp/Mw and eccentricity vector
components for the inner and middle planets. d–f, Mp/Mw and eccentricity
vector components for the middle and outer planets. Panels g, h and i compare
Kepler-138 b’s Mp/Mw and its orbital eccentricity, for three eccentricity priors:
a uniform prior on eccentricity (g), and models with a Rayleigh distribution of
scale factor 0.1 (h), and 0.02 (i).
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12. Extended Data Figure 6 | Posterior distributions for mass ratios and
relative eccentricities between planets. The mass ratio of theinner andmiddle
planets is shown in a, and relative eccentricity vector components—that is, the
difference in ecosv (esinv) in the inner pair—are shown in b (c). The mass
ratio of the middle and outer planets are plotted in d, and the relative
eccentricity vector components—that is, the difference in ecosv (esinv) in the
outer pair—are shown in e (f).
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13. Extended Data Figure 7 | Sensitivity tests for the effects of eccentricity
prior, outlying transit times and free inclinations on the mass of Kepler-138
b relative to the host star. Panel a compares a uniform prior (black curve, our
nominal posterior for all comparisons) and a Rayleigh distribution with scale
factors 0.1 (navy) and 0.02 (cyan). Panel b compares posteriors with 3s outliers
excluded (black), with two alternatives: 4s outliers (blue) and 2.5s outliers
removed (light green). Panel c compares our nominal model with one with a
free ascending node for the inner (purple) or outer (red) planet.
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14. Extended Data Figure 8 | Validation of our method with synthetic data sets.
The green curve marks the posterior for a synthetic data set generated with the
same parameters as were the medians of our nominal posteriors (in Table 1).
The agreement between the green and black curves validates our method and
our claim for a positive mass detection for Kepler-138 b. The magenta and
purple shades are posteriors for models using data generated with zero mass for
Kepler-138 b. These zero-mass synthetic models all reproduced non-
detections.
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15. Extended Data Table 1 | Transit times of Kepler-138’s planets
All times are expressed in days since BJD 2,454,900. Estimated uncertainties give 68% confidence limits. Outliers beyond 3s in the residuals of dynamical fits are marked with an asterisk.
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16. Extended Data Table 2 | Confidence intervals from distributions found with differential evolution Markov Chain Monte Carlo TTV analysis.
We include the parameters of our dynamical fits, as well as the mass ratios and relative eccentricity vector components between the planets, which have tighter constraints than the absolute masses or eccentricity
vector components.
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