This research article explores how the orbital configuration of Kepler-62f, a potentially habitable exoplanet in a five-planet system, could affect its climate and habitability. N-body simulations were used to determine the stable range of orbital eccentricities for Kepler-62f. Climate simulations using two global climate models then examined the planet's surface habitability across this range of eccentricities and for different atmospheric compositions. The simulations found multiple combinations of orbital and atmospheric parameters that could allow for surface liquid water on Kepler-62f, including higher orbital eccentricities coupled with high planetary obliquity or atmospheric CO2 levels above 3 bars.
Is there an_exoplanet_in_the_solar_systemSérgio Sacani
We investigate the prospects for the capture of the proposed Planet 9 from other
stars in the Sun’s birth cluster. Any capture scenario must satisfy three conditions:
the encounter must be more distant than ∼ 150 au to avoid perturbing the Kuiper
belt; the other star must have a wide-orbit planet (a & 100 au); the planet must be
captured onto an appropriate orbit to sculpt the orbital distribution of wide-orbit
Solar System bodies. Here we use N-body simulations to show that these criteria may
be simultaneously satisfied. In a few percent of slow close encounters in a cluster,
bodies are captured onto heliocentric, Planet 9-like orbits. During the ∼ 100 Myr
cluster phase, many stars are likely to host planets on highly-eccentric orbits with
apastron distances beyond 100 au if Neptune-sized planets are common and susceptible
to planet–planet scattering. While the existence of Planet 9 remains unproven, we
consider capture from one of the Sun’s young brethren a plausible route to explain such
an object’s orbit. Capture appears to predict a large population of Trans-Neptunian
Objects (TNOs) whose orbits are aligned with the captured planet, and we propose
that different formation mechanisms will be distinguishable based on their imprint on
the distribution of TNOs
A 2 4_determination_of_the_local_value_of_the_hubble_constantSérgio Sacani
We use the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST) to
reduce the uncertainty in the local value of the Hubble constant from 3.3% to 2.4%.
The bulk of this improvement comes from new, near-infrared observations of Cepheid
variables in 11 host galaxies of recent type Ia supernovae (SNe Ia), more than doubling
the sample of reliable SNe Ia having a Cepheid-calibrated distance to a total of 19; these
in turn leverage the magnitude-redshift relation based on 300 SNe Ia at z <0.15. All
19 hosts as well as the megamaser system NGC4258 have been observed with WFC3
in the optical and near-infrared, thus nullifying cross-instrument zeropoint errors in the
relative distance estimates from Cepheids. Other noteworthy improvements include a
33% reduction in the systematic uncertainty in the maser distance to NGC4258, a larger
sample of Cepheids in the Large Magellanic Cloud (LMC), a more robust distance to
the LMC based on late-type detached eclipsing binaries (DEBs), HST observations of
Cepheids in M31, and new HST-based trigonometric parallaxes for Milky Way (MW)
Cepheids.
We report the discovery of a new Kepler transiting circumbinary planet (CBP).
This latest addition to the still-small family of CBPs defies the current trend of known
short-period planets orbiting near the stability limit of binary stars. Unlike the previous
discoveries, the planet revolving around the eclipsing binary system Kepler-1647 has
a very long orbital period ( 1100 days) and was at conjunction only twice during
the Kepler mission lifetime. Due to the singular configuration of the system, Kepler-
1647b is not only the longest-period transiting CBP at the time of writing, but also one
of the longest-period transiting planets. With a radius of 1:060:01 RJup it is also the
largest CBP to date. The planet produced three transits in the light-curve of Kepler-
1647 (one of them during an eclipse, creating a syzygy) and measurably perturbed the
times of the stellar eclipses, allowing us to measure its mass to be 1:520:65 MJup.
The planet revolves around an 11-day period eclipsing binary consisting of two Solarmass
stars on a slightly inclined, mildly eccentric (ebin = 0:16), spin-synchronized
orbit. Despite having an orbital period three times longer than Earth’s, Kepler-1647b is
in the conservative habitable zone of the binary star throughout its orbit.
The canarias einstein_ring_a_newly_discovered_optical_einstein_ringSérgio Sacani
We report the discovery of an optical Einstein Ring in the Sculptor constellation,
IAC J010127-334319, in the vicinity of the Sculptor Dwarf Spheroidal Galaxy. It is
an almost complete ring ( 300◦) with a diameter of 4.5 arcsec. The discovery was
made serendipitously from inspecting Dark Energy Camera (DECam) archive imaging
data. Confirmation of the object nature has been obtained by deriving spectroscopic
redshifts for both components, lens and source, from observations at the 10.4 m Gran
Telescopio CANARIAS (GTC) with the spectrograph OSIRIS. The lens, a massive
early-type galaxy, has a redshift of z = 0.581 while the source is a starburst galaxy
with redshift of z = 1.165. The total enclosed mass that produces the lensing effect
has been estimated to be Mtot = (1.86 ± 0.23) · 1012M⊙.
We present deep optical images of the Large and Small Magellanic Clouds (LMC and SMC) using
a low cost telephoto lens with a wide field of view to explore stellar substructure in the outskirts
of the stellar disk of the LMC (r < 10 degrees from the center). These data have higher resolution
than existing star count maps, and highlight the existence of stellar arcs and multiple spiral arms in
the northern periphery, with no comparable counterparts in the South. We compare these data to
detailed simulations of the LMC disk outskirts, following interactions with its low mass companion,
the SMC. We consider interaction in isolation and with the inclusion of the Milky Way tidal field.
The simulations are used to assess the origin of the northern structures, including also the low density
stellar arc recently identified in the DES data by Mackey et al. (2015) at ∼ 15 degrees. We conclude
that repeated close interactions with the SMC are primarily responsible for the asymmetric stellar
structures seen in the periphery of the LMC. The orientation and density of these arcs can be used to
constrain the LMC’s interaction history with and impact parameter of the SMC. More generally, we
find that such asymmetric structures should be ubiquitous about pairs of dwarfs and can persist for
1-2 Gyr even after the secondary merges entirely with the primary. As such, the lack of a companion
around a Magellanic Irregular does not disprove the hypothesis that their asymmetric structures are
driven by dwarf-dwarf interactions.
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.
On some structural_features_of_the_metagalaxySérgio Sacani
Progress in a group of investigations designed
to discover some of the structural details in individual galaxies and in the
Metagalaxy is reported in the following pages.
(a) The first section is concerned with the distribution of cluster-type
Cepheids in high galactic latitude. To the 169 already known in latitudes,
greater than or equal to ± 20o
, the systematic variable star programme carried
on at Harvard has added 312, mostly fainter than magnitude 13-0. With
allowance for absorption and for uncertainties yet remaining in the mean
absolute magnitude of these stars, the thickness of the Milky Way, so far
as this type of star is concerned, is not less than twenty-five kiloparsecs ;
he extent of the Milky Way in its own plane, by the same criterion, is more
than thirty kiloparsecs, perhaps much more.
(b) The extent of the Milky Way in the anti-centre quadrant is considered
on the basis of classical and cluster-type Cepheids ; provisionally
it is found that the galactic system reaches to a distance of at least ten
kiloparsecs in longitude 150o
.
(r) More than six hundred new variables have been found in the Large
Magellanic Cloud and measured for position, ranges and median magnitudes ;
the frequency of periods is not unlike that for the classical Cepheids in the
galactic system ; the light curves also are comparable in all details. The
Magellanic Cepheids, like the galactic classical Cepheids, are concentrated
in regions of high star-density.
(d) Further study of the period-luminosity relation in the Large Magellanic
Cloud permits its revision and strengthening for the Cepheids of
highest absolute magnitude. An observed deviation from the relation
that had previously been found for the Small Cloud is probably to be
attributed to scale error in the magnitude system. No seriously disturbing
Detection of solar_like_oscillations_in_relies_of_the_milk_way_asteroseismolo...Sérgio Sacani
Asteroseismic constraints on K giants make it possible to infer radii, masses and ages of tens
of thousands of field stars. Tests against independent estimates of these properties are however
scarce, especially in the metal-poor regime. Here, we report the detection of solar-like
oscillations in 8 stars belonging to the red-giant branch and red-horizontal branch of the globular
cluster M4. The detections were made in photometric observations from the K2 Mission
during its Campaign 2. Making use of independent constraints on the distance, we estimate
masses of the 8 stars by utilising different combinations of seismic and non-seismic inputs.
When introducing a correction to the Δν scaling relation as suggested by stellar models, for
RGB stars we find excellent agreement with the expected masses from isochrone fitting, and
with a distance modulus derived using independent methods. The offset with respect to independent
masses is lower, or comparable with, the uncertainties on the average RGB mass
(4 − 10%, depending on the combination of constraints used). Our results lend confidence to
asteroseismic masses in the metal poor regime. We note that a larger sample will be needed
to allow more stringent tests to be made of systematic uncertainties in all the observables
(both seismic and non-seismic), and to explore the properties of RHB stars, and of different
populations in the cluster.
Is there an_exoplanet_in_the_solar_systemSérgio Sacani
We investigate the prospects for the capture of the proposed Planet 9 from other
stars in the Sun’s birth cluster. Any capture scenario must satisfy three conditions:
the encounter must be more distant than ∼ 150 au to avoid perturbing the Kuiper
belt; the other star must have a wide-orbit planet (a & 100 au); the planet must be
captured onto an appropriate orbit to sculpt the orbital distribution of wide-orbit
Solar System bodies. Here we use N-body simulations to show that these criteria may
be simultaneously satisfied. In a few percent of slow close encounters in a cluster,
bodies are captured onto heliocentric, Planet 9-like orbits. During the ∼ 100 Myr
cluster phase, many stars are likely to host planets on highly-eccentric orbits with
apastron distances beyond 100 au if Neptune-sized planets are common and susceptible
to planet–planet scattering. While the existence of Planet 9 remains unproven, we
consider capture from one of the Sun’s young brethren a plausible route to explain such
an object’s orbit. Capture appears to predict a large population of Trans-Neptunian
Objects (TNOs) whose orbits are aligned with the captured planet, and we propose
that different formation mechanisms will be distinguishable based on their imprint on
the distribution of TNOs
A 2 4_determination_of_the_local_value_of_the_hubble_constantSérgio Sacani
We use the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST) to
reduce the uncertainty in the local value of the Hubble constant from 3.3% to 2.4%.
The bulk of this improvement comes from new, near-infrared observations of Cepheid
variables in 11 host galaxies of recent type Ia supernovae (SNe Ia), more than doubling
the sample of reliable SNe Ia having a Cepheid-calibrated distance to a total of 19; these
in turn leverage the magnitude-redshift relation based on 300 SNe Ia at z <0.15. All
19 hosts as well as the megamaser system NGC4258 have been observed with WFC3
in the optical and near-infrared, thus nullifying cross-instrument zeropoint errors in the
relative distance estimates from Cepheids. Other noteworthy improvements include a
33% reduction in the systematic uncertainty in the maser distance to NGC4258, a larger
sample of Cepheids in the Large Magellanic Cloud (LMC), a more robust distance to
the LMC based on late-type detached eclipsing binaries (DEBs), HST observations of
Cepheids in M31, and new HST-based trigonometric parallaxes for Milky Way (MW)
Cepheids.
We report the discovery of a new Kepler transiting circumbinary planet (CBP).
This latest addition to the still-small family of CBPs defies the current trend of known
short-period planets orbiting near the stability limit of binary stars. Unlike the previous
discoveries, the planet revolving around the eclipsing binary system Kepler-1647 has
a very long orbital period ( 1100 days) and was at conjunction only twice during
the Kepler mission lifetime. Due to the singular configuration of the system, Kepler-
1647b is not only the longest-period transiting CBP at the time of writing, but also one
of the longest-period transiting planets. With a radius of 1:060:01 RJup it is also the
largest CBP to date. The planet produced three transits in the light-curve of Kepler-
1647 (one of them during an eclipse, creating a syzygy) and measurably perturbed the
times of the stellar eclipses, allowing us to measure its mass to be 1:520:65 MJup.
The planet revolves around an 11-day period eclipsing binary consisting of two Solarmass
stars on a slightly inclined, mildly eccentric (ebin = 0:16), spin-synchronized
orbit. Despite having an orbital period three times longer than Earth’s, Kepler-1647b is
in the conservative habitable zone of the binary star throughout its orbit.
The canarias einstein_ring_a_newly_discovered_optical_einstein_ringSérgio Sacani
We report the discovery of an optical Einstein Ring in the Sculptor constellation,
IAC J010127-334319, in the vicinity of the Sculptor Dwarf Spheroidal Galaxy. It is
an almost complete ring ( 300◦) with a diameter of 4.5 arcsec. The discovery was
made serendipitously from inspecting Dark Energy Camera (DECam) archive imaging
data. Confirmation of the object nature has been obtained by deriving spectroscopic
redshifts for both components, lens and source, from observations at the 10.4 m Gran
Telescopio CANARIAS (GTC) with the spectrograph OSIRIS. The lens, a massive
early-type galaxy, has a redshift of z = 0.581 while the source is a starburst galaxy
with redshift of z = 1.165. The total enclosed mass that produces the lensing effect
has been estimated to be Mtot = (1.86 ± 0.23) · 1012M⊙.
We present deep optical images of the Large and Small Magellanic Clouds (LMC and SMC) using
a low cost telephoto lens with a wide field of view to explore stellar substructure in the outskirts
of the stellar disk of the LMC (r < 10 degrees from the center). These data have higher resolution
than existing star count maps, and highlight the existence of stellar arcs and multiple spiral arms in
the northern periphery, with no comparable counterparts in the South. We compare these data to
detailed simulations of the LMC disk outskirts, following interactions with its low mass companion,
the SMC. We consider interaction in isolation and with the inclusion of the Milky Way tidal field.
The simulations are used to assess the origin of the northern structures, including also the low density
stellar arc recently identified in the DES data by Mackey et al. (2015) at ∼ 15 degrees. We conclude
that repeated close interactions with the SMC are primarily responsible for the asymmetric stellar
structures seen in the periphery of the LMC. The orientation and density of these arcs can be used to
constrain the LMC’s interaction history with and impact parameter of the SMC. More generally, we
find that such asymmetric structures should be ubiquitous about pairs of dwarfs and can persist for
1-2 Gyr even after the secondary merges entirely with the primary. As such, the lack of a companion
around a Magellanic Irregular does not disprove the hypothesis that their asymmetric structures are
driven by dwarf-dwarf interactions.
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.
On some structural_features_of_the_metagalaxySérgio Sacani
Progress in a group of investigations designed
to discover some of the structural details in individual galaxies and in the
Metagalaxy is reported in the following pages.
(a) The first section is concerned with the distribution of cluster-type
Cepheids in high galactic latitude. To the 169 already known in latitudes,
greater than or equal to ± 20o
, the systematic variable star programme carried
on at Harvard has added 312, mostly fainter than magnitude 13-0. With
allowance for absorption and for uncertainties yet remaining in the mean
absolute magnitude of these stars, the thickness of the Milky Way, so far
as this type of star is concerned, is not less than twenty-five kiloparsecs ;
he extent of the Milky Way in its own plane, by the same criterion, is more
than thirty kiloparsecs, perhaps much more.
(b) The extent of the Milky Way in the anti-centre quadrant is considered
on the basis of classical and cluster-type Cepheids ; provisionally
it is found that the galactic system reaches to a distance of at least ten
kiloparsecs in longitude 150o
.
(r) More than six hundred new variables have been found in the Large
Magellanic Cloud and measured for position, ranges and median magnitudes ;
the frequency of periods is not unlike that for the classical Cepheids in the
galactic system ; the light curves also are comparable in all details. The
Magellanic Cepheids, like the galactic classical Cepheids, are concentrated
in regions of high star-density.
(d) Further study of the period-luminosity relation in the Large Magellanic
Cloud permits its revision and strengthening for the Cepheids of
highest absolute magnitude. An observed deviation from the relation
that had previously been found for the Small Cloud is probably to be
attributed to scale error in the magnitude system. No seriously disturbing
Detection of solar_like_oscillations_in_relies_of_the_milk_way_asteroseismolo...Sérgio Sacani
Asteroseismic constraints on K giants make it possible to infer radii, masses and ages of tens
of thousands of field stars. Tests against independent estimates of these properties are however
scarce, especially in the metal-poor regime. Here, we report the detection of solar-like
oscillations in 8 stars belonging to the red-giant branch and red-horizontal branch of the globular
cluster M4. The detections were made in photometric observations from the K2 Mission
during its Campaign 2. Making use of independent constraints on the distance, we estimate
masses of the 8 stars by utilising different combinations of seismic and non-seismic inputs.
When introducing a correction to the Δν scaling relation as suggested by stellar models, for
RGB stars we find excellent agreement with the expected masses from isochrone fitting, and
with a distance modulus derived using independent methods. The offset with respect to independent
masses is lower, or comparable with, the uncertainties on the average RGB mass
(4 − 10%, depending on the combination of constraints used). Our results lend confidence to
asteroseismic masses in the metal poor regime. We note that a larger sample will be needed
to allow more stringent tests to be made of systematic uncertainties in all the observables
(both seismic and non-seismic), and to explore the properties of RHB stars, and of different
populations in the cluster.
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.
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.
The importance of comets for the origin of life on Earth has been advocated for many decades. Amino acids are
key ingredients in chemistry, leading to life as we know it. Many primitive meteorites contain amino acids, and it
is generally believed that these are formed by aqueous alterations. In the collector aerogel and foil samples of the
Stardust mission after the flyby at comet Wild 2, the simplest form of amino acids, glycine, has been found
together with precursor molecules methylamine and ethylamine. Because of contamination issues of the samples,
a cometary origin was deduced from the 13C isotopic signature. We report the presence of volatile glycine
accompanied by methylamine and ethylamine in the coma of 67P/Churyumov-Gerasimenko measured by
the ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) mass spectrometer, confirming the
Stardust results. Together with the detection of phosphorus and a multitude of organic molecules, this result
demonstrates that comets could have played a crucial role in the emergence of life on Earth.
TEMPORAL EVOLUTION OF THE HIGH-ENERGY IRRADIATION AND WATER CONTENT OF TRAPPI...Sérgio Sacani
The ultracool dwarf star TRAPPIST-1 hosts seven Earth-size transiting planets, some of which could
harbour liquid water on their surfaces. UV observations are essential to measure their high-energy
irradiation, and to search for photodissociated water escaping from their putative atmospheres. Our
new observations of TRAPPIST-1 Ly-α line during the transit of TRAPPIST-1c show an evolution of
the star emission over three months, preventing us from assessing the presence of an extended hydrogen
exosphere. Based on the current knowledge of the stellar irradiation, we investigated the likely history
of water loss in the system. Planets b to d might still be in a runaway phase, and planets within the
orbit of TRAPPIST-1g could have lost more than 20 Earth oceans after 8 Gyr of hydrodynamic escape.
However, TRAPPIST-1e to h might have lost less than 3 Earth oceans if hydrodynamic escape stopped
once they entered the habitable zone. We caution that these estimates remain limited by the large
uncertainty on the planet masses. They likely represent upper limits on the actual water loss because
our assumptions maximize the XUV-driven escape, while photodissociation in the upper atmospheres
should be the limiting process. Late-stage outgassing could also have contributed significant amounts
of water for the outer, more massive planets after they entered the habitable zone. While our results
suggest that the outer planets are the best candidates to search for water with the JWST, they also
highlight the need for theoretical studies and complementary observations in all wavelength domains
to determine the nature of the TRAPPIST-1 planets, and their potential habitability.
Keywords: planetary systems - Stars: individual: TRAPPIST-1
SPECTROSCOPIC CONFIRMATION OF THE EXISTENCE OF LARGE, DIFFUSE GALAXIES IN THE...Sérgio Sacani
We recently identified a population of low surface brightness objects in the field of the z = 0.023 Coma cluster,
using the Dragonfly Telephoto Array. Here we present Keck spectroscopy of one of the largest of these “ultradiffuse
galaxies” (UDGs), confirming that it is a member of the cluster. The galaxy has prominent absorption
features, including the Ca II H+K lines and the G-band, and no detected emission lines. Its radial velocity of
cz=6280±120 km s−1 is within the 1σ velocity dispersion of the Coma cluster. The galaxy has an effective
radius of 4.3 ± 0.3 kpc and a Sérsic index of 0.89 ± 0.06, as measured from Keck imaging. We find no indications
of tidal tails or other distortions, at least out to a radius of ∼2re. We show that UDGs are located in a previously
sparsely populated region of the size—magnitude plane of quiescent stellar systems, as they are ∼6 mag fainter
than normal early-type galaxies of the same size. It appears that the luminosity distribution of large quiescent
galaxies is not continuous, although this could largely be due to selection effects. Dynamical measurements are
needed to determine whether the dark matter halos of UDGs are similar to those of galaxies with the same
luminosity or to those of galaxies with the same size.
Proper-motion age dating of the progeny of Nova Scorpii ad 1437Sérgio Sacani
‘Cataclysmic variables’ are binary star systems in which one
star of the pair is a white dwarf, and which often generate bright
and energetic stellar outbursts. Classical novae are one type of
outburst: when the white dwarf accretes enough matter from its
companion, the resulting hydrogen-rich atmospheric envelope
can host a runaway thermonuclear reaction that generates a rapid
brightening1–4. Achieving peak luminosities of up to one million
times that of the Sun5
, all classical novae are recurrent, on timescales
of months6
to millennia7
. During the century before and after an
eruption, the ‘novalike’ binary systems that give rise to classical
novae exhibit high rates of mass transfer to their white dwarfs8
.
Another type of outburst is the dwarf nova: these occur in binaries
that have stellar masses and periods indistinguishable from those
of novalikes9
but much lower mass-transfer rates10, when accretiondisk
instabilities11 drop matter onto the white dwarfs. The coexistence
at the same orbital period of novalike binaries and dwarf
novae—which are identical but for their widely varying accretion
rates—has been a longstanding puzzle9
. Here we report the recovery
of the binary star underlying the classical nova eruption of 11 March
ad 1437 (refs 12, 13), and independently confirm its age by propermotion
dating. We show that, almost 500 years after a classical-nova
event, the system exhibited dwarf-nova eruptions. The three other
oldest recovered classical novae14–16 display nova shells, but lack
firm post-eruption ages17,18, and are also dwarf novae at present.
We conclude that many old novae become dwarf novae for part of
the millennia between successive nova eruptions19,
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.
EXTINCTION AND THE DIMMING OF KIC 8462852Sérgio Sacani
To test alternative hypotheses for the behavior of KIC 8462852, we obtained measurements of the star
over a wide wavelength range from the UV to the mid-infrared from October 2015 through December
2016, using Swift, Spitzer and at AstroLAB IRIS. The star faded in a manner similar to the longterm
fading seen in Kepler data about 1400 days previously. The dimming rate for the entire period
reported is 22.1 ± 9.7 milli-mag yr−1
in the Swift wavebands, with amounts of 21.0 ± 4.5 mmag in
the groundbased B measurements, 14.0 ± 4.5 mmag in V , and 13.0 ± 4.5 in R, and a rate of 5.0 ± 1.2
mmag yr−1 averaged over the two warm Spitzer bands. Although the dimming is small, it is seen at
& 3 σ by three different observatories operating from the UV to the IR. The presence of long-term
secular dimming means that previous SED models of the star based on photometric measurements
taken years apart may not be accurate. We find that stellar models with Tef f = 7000 - 7100 K and
AV ∼ 0.73 best fit the Swift data from UV to optical. These models also show no excess in the
near-simultaneous Spitzer photometry at 3.6 and 4.5 µm, although a longer wavelength excess from
a substantial debris disk is still possible (e.g., as around Fomalhaut). The wavelength dependence of
the fading favors a relatively neutral color (i.e., RV & 5, but not flat across all the bands) compared
with the extinction law for the general ISM (RV = 3.1), suggesting that the dimming arises from
circumstellar material
WHERE IS THE FLUX GOING? THE LONG-TERM PHOTOMETRIC VARIABILITY OF BOYAJIAN’S ...Sérgio Sacani
We present ∼ 800 days of photometric monitoring of Boyajian’s Star (KIC 8462852) from the AllSky
Automated Survey for Supernovae (ASAS-SN) and ∼ 4000 days of monitoring from the All Sky
Automated Survey (ASAS). We show that from 2015 to the present the brightness of Boyajian’s Star
has steadily decreased at a rate of 6.3 ± 1.4 mmag yr−1
, such that the star is now 1.5% fainter than it
was in February 2015. Moreover, the longer time baseline afforded by ASAS suggests that Boyajian’s
Star has also undergone two brightening episodes in the past 11 years, rather than only exhibiting a
monotonic decline. We analyze a sample of ∼ 1000 comparison stars of similar brightness located in
the same ASAS-SN field and demonstrate that the recent fading is significant at & 99.4% confidence.
The 2015 − 2017 dimming rate is consistent with that measured with Kepler data for the time period
from 2009 to 2013. This long-term variability is difficult to explain with any of the physical models
for the star’s behavior proposed to date
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.
Supermassive black holes in galaxy centres can grow by the accretion
of gas, liberating enormous amounts of energy that might
regulate star formation on galaxy-wide scales1–3
. The nature of
gaseous fuel reservoirs that power black hole growth is nevertheless
largely unconstrained by observations, and is instead routinely
simplified as a smooth, spherical inflow of very hot gas
in accordance with the Bondi solution4
. Recent theory5–7 and
simulations8–10 instead predict that accretion can be dominated by
a stochastic, clumpy distribution of very cold molecular clouds,
though unambiguous observational support for this prediction remains
elusive. Here we show observational evidence for a cold,
clumpy accretion flow toward a supermassive black hole fuel reservoir
in the nucleus of the Abell 2597 Brightest Cluster Galaxy
(BCG), a nearby (z = 0.0821) giant elliptical galaxy surrounded
by a dense halo of hot plasma11–13. Under the right conditions,
thermal instabilities can precipitate from this hot gas, producing a
rain of cold clouds that fall toward the galaxy’s centre14, sustaining
star formation amid a kiloparsec-scale molecular nebula that inhabits
its core15. New interferometric sub-millimetre observations
show that these cold clouds also fuel black hole accretion, revealing
“shadows” cast by molecular clouds as they move inward at ∼ 300
km s−1
toward the active supermassive black hole in the galaxy
centre, which serves as a bright backlight. Corroborating evidence
from prior observations16 of warmer atomic gas at extremely high
spatial resolution17, along with simple arguments based on geometry
and probability, indicates that these clouds are within the innermost
hundred parsecs of the black hole, and falling closer toward
it
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
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.
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
Magnetic interaction of_a_super_cme_with_the_earths_magnetosphere_scenario_fo...Sérgio Sacani
Solar eruptions, known as Coronal Mass Ejections (CMEs), are
frequently observed on our Sun. Recent Kepler observations of super
ares
on G-type stars have implied that so called super-CMEs, possessing kinetic
energies 10 times of the most powerful CME event ever observed on the Sun,
could be produced with a frequency of 1 event per 800-2000 yr on solar-
like slowly rotating stars. We have performed a 3D time-dependent global
magnetohydrodynamic simulation of the magnetic interaction of such a CME
cloud with the Earth's magnetosphere. We calculated the global structure
of the perturbed magnetosphere and derive the latitude of the open-closed
magnetic eld boundary. We also estimated energy
uxes penetrating the
Earth's ionosphere and discuss the consequences of energetic particle
uxes
on biological systems on early Earth.
The Variable Detection of Atmospheric Escape around the Young, Hot Neptune AU...Sérgio Sacani
Photoevaporation is a potential explanation for several features within exoplanet demographics. Atmospheric escape
observed in young Neptune-sized exoplanets can provide insight into and characterize which mechanisms drive this
evolution and at what times they dominate. AU Mic b is one such exoplanet, slightly larger than Neptune (4.19 R⊕).
It closely orbits a 23 Myr pre-main-sequence M dwarf with an orbital period of 8.46 days. We obtained two visits of
AU Mic b at Lyα with Hubble Space Telescope (HST)/Space Telescope Imaging Spectrograph. One flare within the
first HST visit is characterized and removed from our search for a planetary transit. We present a nondetection in our
first visit, followed by the detection of escaping neutral hydrogen ahead of the planet in our second visit. The outflow
absorbed ∼30% of the star’s Lyα blue wing 2.5 hr before the planet’s white-light transit. We estimate that the
highest-velocity escaping material has a column density of 1013.96 cm−2 and is moving 61.26 km s−1 away from the
host star. AU Mic b’s large high-energy irradiation could photoionize its escaping neutral hydrogen in 44 minutes,
rendering it temporarily unobservable. Our time-variable Lyα transit ahead of AU Mic b could also be explained by
an intermediate stellar wind strength from AU Mic that shapes the escaping material into a leading tail. Future Lyα
observations of this system will confirm and characterize the unique variable nature of its Lyα transit, which,
combined with modeling, will tune the importance of stellar wind and photoionization.
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.
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.
The importance of comets for the origin of life on Earth has been advocated for many decades. Amino acids are
key ingredients in chemistry, leading to life as we know it. Many primitive meteorites contain amino acids, and it
is generally believed that these are formed by aqueous alterations. In the collector aerogel and foil samples of the
Stardust mission after the flyby at comet Wild 2, the simplest form of amino acids, glycine, has been found
together with precursor molecules methylamine and ethylamine. Because of contamination issues of the samples,
a cometary origin was deduced from the 13C isotopic signature. We report the presence of volatile glycine
accompanied by methylamine and ethylamine in the coma of 67P/Churyumov-Gerasimenko measured by
the ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) mass spectrometer, confirming the
Stardust results. Together with the detection of phosphorus and a multitude of organic molecules, this result
demonstrates that comets could have played a crucial role in the emergence of life on Earth.
TEMPORAL EVOLUTION OF THE HIGH-ENERGY IRRADIATION AND WATER CONTENT OF TRAPPI...Sérgio Sacani
The ultracool dwarf star TRAPPIST-1 hosts seven Earth-size transiting planets, some of which could
harbour liquid water on their surfaces. UV observations are essential to measure their high-energy
irradiation, and to search for photodissociated water escaping from their putative atmospheres. Our
new observations of TRAPPIST-1 Ly-α line during the transit of TRAPPIST-1c show an evolution of
the star emission over three months, preventing us from assessing the presence of an extended hydrogen
exosphere. Based on the current knowledge of the stellar irradiation, we investigated the likely history
of water loss in the system. Planets b to d might still be in a runaway phase, and planets within the
orbit of TRAPPIST-1g could have lost more than 20 Earth oceans after 8 Gyr of hydrodynamic escape.
However, TRAPPIST-1e to h might have lost less than 3 Earth oceans if hydrodynamic escape stopped
once they entered the habitable zone. We caution that these estimates remain limited by the large
uncertainty on the planet masses. They likely represent upper limits on the actual water loss because
our assumptions maximize the XUV-driven escape, while photodissociation in the upper atmospheres
should be the limiting process. Late-stage outgassing could also have contributed significant amounts
of water for the outer, more massive planets after they entered the habitable zone. While our results
suggest that the outer planets are the best candidates to search for water with the JWST, they also
highlight the need for theoretical studies and complementary observations in all wavelength domains
to determine the nature of the TRAPPIST-1 planets, and their potential habitability.
Keywords: planetary systems - Stars: individual: TRAPPIST-1
SPECTROSCOPIC CONFIRMATION OF THE EXISTENCE OF LARGE, DIFFUSE GALAXIES IN THE...Sérgio Sacani
We recently identified a population of low surface brightness objects in the field of the z = 0.023 Coma cluster,
using the Dragonfly Telephoto Array. Here we present Keck spectroscopy of one of the largest of these “ultradiffuse
galaxies” (UDGs), confirming that it is a member of the cluster. The galaxy has prominent absorption
features, including the Ca II H+K lines and the G-band, and no detected emission lines. Its radial velocity of
cz=6280±120 km s−1 is within the 1σ velocity dispersion of the Coma cluster. The galaxy has an effective
radius of 4.3 ± 0.3 kpc and a Sérsic index of 0.89 ± 0.06, as measured from Keck imaging. We find no indications
of tidal tails or other distortions, at least out to a radius of ∼2re. We show that UDGs are located in a previously
sparsely populated region of the size—magnitude plane of quiescent stellar systems, as they are ∼6 mag fainter
than normal early-type galaxies of the same size. It appears that the luminosity distribution of large quiescent
galaxies is not continuous, although this could largely be due to selection effects. Dynamical measurements are
needed to determine whether the dark matter halos of UDGs are similar to those of galaxies with the same
luminosity or to those of galaxies with the same size.
Proper-motion age dating of the progeny of Nova Scorpii ad 1437Sérgio Sacani
‘Cataclysmic variables’ are binary star systems in which one
star of the pair is a white dwarf, and which often generate bright
and energetic stellar outbursts. Classical novae are one type of
outburst: when the white dwarf accretes enough matter from its
companion, the resulting hydrogen-rich atmospheric envelope
can host a runaway thermonuclear reaction that generates a rapid
brightening1–4. Achieving peak luminosities of up to one million
times that of the Sun5
, all classical novae are recurrent, on timescales
of months6
to millennia7
. During the century before and after an
eruption, the ‘novalike’ binary systems that give rise to classical
novae exhibit high rates of mass transfer to their white dwarfs8
.
Another type of outburst is the dwarf nova: these occur in binaries
that have stellar masses and periods indistinguishable from those
of novalikes9
but much lower mass-transfer rates10, when accretiondisk
instabilities11 drop matter onto the white dwarfs. The coexistence
at the same orbital period of novalike binaries and dwarf
novae—which are identical but for their widely varying accretion
rates—has been a longstanding puzzle9
. Here we report the recovery
of the binary star underlying the classical nova eruption of 11 March
ad 1437 (refs 12, 13), and independently confirm its age by propermotion
dating. We show that, almost 500 years after a classical-nova
event, the system exhibited dwarf-nova eruptions. The three other
oldest recovered classical novae14–16 display nova shells, but lack
firm post-eruption ages17,18, and are also dwarf novae at present.
We conclude that many old novae become dwarf novae for part of
the millennia between successive nova eruptions19,
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.
EXTINCTION AND THE DIMMING OF KIC 8462852Sérgio Sacani
To test alternative hypotheses for the behavior of KIC 8462852, we obtained measurements of the star
over a wide wavelength range from the UV to the mid-infrared from October 2015 through December
2016, using Swift, Spitzer and at AstroLAB IRIS. The star faded in a manner similar to the longterm
fading seen in Kepler data about 1400 days previously. The dimming rate for the entire period
reported is 22.1 ± 9.7 milli-mag yr−1
in the Swift wavebands, with amounts of 21.0 ± 4.5 mmag in
the groundbased B measurements, 14.0 ± 4.5 mmag in V , and 13.0 ± 4.5 in R, and a rate of 5.0 ± 1.2
mmag yr−1 averaged over the two warm Spitzer bands. Although the dimming is small, it is seen at
& 3 σ by three different observatories operating from the UV to the IR. The presence of long-term
secular dimming means that previous SED models of the star based on photometric measurements
taken years apart may not be accurate. We find that stellar models with Tef f = 7000 - 7100 K and
AV ∼ 0.73 best fit the Swift data from UV to optical. These models also show no excess in the
near-simultaneous Spitzer photometry at 3.6 and 4.5 µm, although a longer wavelength excess from
a substantial debris disk is still possible (e.g., as around Fomalhaut). The wavelength dependence of
the fading favors a relatively neutral color (i.e., RV & 5, but not flat across all the bands) compared
with the extinction law for the general ISM (RV = 3.1), suggesting that the dimming arises from
circumstellar material
WHERE IS THE FLUX GOING? THE LONG-TERM PHOTOMETRIC VARIABILITY OF BOYAJIAN’S ...Sérgio Sacani
We present ∼ 800 days of photometric monitoring of Boyajian’s Star (KIC 8462852) from the AllSky
Automated Survey for Supernovae (ASAS-SN) and ∼ 4000 days of monitoring from the All Sky
Automated Survey (ASAS). We show that from 2015 to the present the brightness of Boyajian’s Star
has steadily decreased at a rate of 6.3 ± 1.4 mmag yr−1
, such that the star is now 1.5% fainter than it
was in February 2015. Moreover, the longer time baseline afforded by ASAS suggests that Boyajian’s
Star has also undergone two brightening episodes in the past 11 years, rather than only exhibiting a
monotonic decline. We analyze a sample of ∼ 1000 comparison stars of similar brightness located in
the same ASAS-SN field and demonstrate that the recent fading is significant at & 99.4% confidence.
The 2015 − 2017 dimming rate is consistent with that measured with Kepler data for the time period
from 2009 to 2013. This long-term variability is difficult to explain with any of the physical models
for the star’s behavior proposed to date
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.
Supermassive black holes in galaxy centres can grow by the accretion
of gas, liberating enormous amounts of energy that might
regulate star formation on galaxy-wide scales1–3
. The nature of
gaseous fuel reservoirs that power black hole growth is nevertheless
largely unconstrained by observations, and is instead routinely
simplified as a smooth, spherical inflow of very hot gas
in accordance with the Bondi solution4
. Recent theory5–7 and
simulations8–10 instead predict that accretion can be dominated by
a stochastic, clumpy distribution of very cold molecular clouds,
though unambiguous observational support for this prediction remains
elusive. Here we show observational evidence for a cold,
clumpy accretion flow toward a supermassive black hole fuel reservoir
in the nucleus of the Abell 2597 Brightest Cluster Galaxy
(BCG), a nearby (z = 0.0821) giant elliptical galaxy surrounded
by a dense halo of hot plasma11–13. Under the right conditions,
thermal instabilities can precipitate from this hot gas, producing a
rain of cold clouds that fall toward the galaxy’s centre14, sustaining
star formation amid a kiloparsec-scale molecular nebula that inhabits
its core15. New interferometric sub-millimetre observations
show that these cold clouds also fuel black hole accretion, revealing
“shadows” cast by molecular clouds as they move inward at ∼ 300
km s−1
toward the active supermassive black hole in the galaxy
centre, which serves as a bright backlight. Corroborating evidence
from prior observations16 of warmer atomic gas at extremely high
spatial resolution17, along with simple arguments based on geometry
and probability, indicates that these clouds are within the innermost
hundred parsecs of the black hole, and falling closer toward
it
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
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.
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
Magnetic interaction of_a_super_cme_with_the_earths_magnetosphere_scenario_fo...Sérgio Sacani
Solar eruptions, known as Coronal Mass Ejections (CMEs), are
frequently observed on our Sun. Recent Kepler observations of super
ares
on G-type stars have implied that so called super-CMEs, possessing kinetic
energies 10 times of the most powerful CME event ever observed on the Sun,
could be produced with a frequency of 1 event per 800-2000 yr on solar-
like slowly rotating stars. We have performed a 3D time-dependent global
magnetohydrodynamic simulation of the magnetic interaction of such a CME
cloud with the Earth's magnetosphere. We calculated the global structure
of the perturbed magnetosphere and derive the latitude of the open-closed
magnetic eld boundary. We also estimated energy
uxes penetrating the
Earth's ionosphere and discuss the consequences of energetic particle
uxes
on biological systems on early Earth.
The Variable Detection of Atmospheric Escape around the Young, Hot Neptune AU...Sérgio Sacani
Photoevaporation is a potential explanation for several features within exoplanet demographics. Atmospheric escape
observed in young Neptune-sized exoplanets can provide insight into and characterize which mechanisms drive this
evolution and at what times they dominate. AU Mic b is one such exoplanet, slightly larger than Neptune (4.19 R⊕).
It closely orbits a 23 Myr pre-main-sequence M dwarf with an orbital period of 8.46 days. We obtained two visits of
AU Mic b at Lyα with Hubble Space Telescope (HST)/Space Telescope Imaging Spectrograph. One flare within the
first HST visit is characterized and removed from our search for a planetary transit. We present a nondetection in our
first visit, followed by the detection of escaping neutral hydrogen ahead of the planet in our second visit. The outflow
absorbed ∼30% of the star’s Lyα blue wing 2.5 hr before the planet’s white-light transit. We estimate that the
highest-velocity escaping material has a column density of 1013.96 cm−2 and is moving 61.26 km s−1 away from the
host star. AU Mic b’s large high-energy irradiation could photoionize its escaping neutral hydrogen in 44 minutes,
rendering it temporarily unobservable. Our time-variable Lyα transit ahead of AU Mic b could also be explained by
an intermediate stellar wind strength from AU Mic that shapes the escaping material into a leading tail. Future Lyα
observations of this system will confirm and characterize the unique variable nature of its Lyα transit, which,
combined with modeling, will tune the importance of stellar wind and photoionization.
Fizzy Super-Earths: Impacts of Magma Composition on the Bulk Density and Stru...Sérgio Sacani
Lava worlds are a potential emerging population of Super-Earths that are on close-in orbits around their host stars,
with likely partially molten mantles. To date, few studies have addressed the impact of magma on the observed
properties of a planet. At ambient conditions, magma is less dense than solid rock; however, it is also more
compressible with increasing pressure. Therefore, it is unclear how large-scale magma oceans affect planet
observables, such as bulk density. We update ExoPlex, a thermodynamically self-consistent planet interior
software, to include anhydrous, hydrous (2.2 wt% H2O), and carbonated magmas (5.2 wt% CO2). We find that
Earth-like planets with magma oceans larger than ∼1.5 R⊕ and ∼3.2 M⊕ are modestly denser than an equivalentmass
solid planet. From our model, three classes of mantle structures emerge for magma ocean planets: (1) a
mantle magma ocean, (2) a surface magma ocean, and (3) one consisting of a surface magma ocean, a solid rock
layer, and a basal magma ocean. The class of planets in which a basal magma ocean is present may sequester
dissolved volatiles on billion-year timescales, in which a 4 M⊕ mass planet can trap more than 130 times the mass
of water than in Earth’s present-day oceans and 1000 times the carbon in the Earth’s surface and crust.
Hot Earth or Young Venus? A nearby transiting rocky planet mysterySérgio Sacani
Venus and Earth provide astonishingly different views of the evolution of a rocky planet, raising the question of why these two rock y worlds evolv ed so differently. The recently disco v ered transiting Super-Earth LP 890-9c (TOI-4306c, SPECULOOS-2c) is a key to the question. It circles a nearby M6V star in 8.46 d. LP890-9c receives similar flux as modern Earth, which puts it very close to the inner edge of the Habitable Zone (HZ), where models differ strongly in their prediction of how long rocky planets can hold onto their water. We model the atmosphere of a hot LP890-9c at the inner edge of the HZ, where the planet could sustain several very different environments. The resulting transmission spectra differ considerably between a hot, wet exo-Earth, a steamy planet caught in a runaway greenhouse, and an exo-Venus. Distinguishing these scenarios from the planet’s spectra will provide critical new insights into the evolution of hot terrestrial planets into exo-Venus. Our model and spectra are available online as a tool to plan observations. They show that observing LP890-9c can provide key insights into the evolution of a rocky planet at the inner edge of the HZ as well as the long-term future of Earth.
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.
Is the atmosphere of the ultra-hot Jupiter WASP-121 b variable?Sérgio Sacani
We present a comprehensive analysis of the Hubble Space Telescope observations of the atmosphere
of WASP-121 b, a ultra-hot Jupiter. After reducing the transit, eclipse, and phase-curve observations
with a uniform methodology and addressing the biases from instrument systematics, sophisticated
atmospheric retrievals are used to extract robust constraints on the thermal structure, chemistry, and
cloud properties of the atmosphere. Our analysis shows that the observations are consistent with a
strong thermal inversion beginning at ∼104 Pa on the dayside, solar to subsolar metallicity Z (i.e.,
−0.77 < log(Z) < 0.05), and super-solar C/O ratio (i.e., 0.59 < C/O < 0.87). More importantly,
utilizing the high signal-to-noise ratio and repeated observations of the planet, we identify the following
unambiguous time-varying signals in the data: i) a shift of the putative hotspot offset between the
two phase-curves and ii) varying spectral signatures in the transits and eclipses. By simulating the
global dynamics of WASP-121 b atmosphere at high-resolution, we show that the identified signals are
consistent with quasi-periodic weather patterns, hence atmospheric variability, with signatures at the
level probed by the observations (∼5% to ∼10%) that change on a timescale of ∼5 planet days; in
the simulations, the weather patterns arise from the formation and movement of storms and fronts,
causing hot (as well as cold) patches of atmosphere to deform, separate, and mix in time.
The Possible Tidal Demise of Kepler’s First Planetary SystemSérgio Sacani
We present evidence of tidally-driven inspiral in the Kepler-1658 (KOI-4) system, which consists of a giant planet
(1.1RJ, 5.9MJ) orbiting an evolved host star (2.9Re, 1.5Me). Using transit timing measurements from Kepler,
Palomar/WIRC, and TESS, we show that the orbital period of Kepler-1658b appears to be decreasing at a rate = -
+ P 131 22
20 ms yr−1
, corresponding to an infall timescale P P » 2.5 Myr. We consider other explanations for the
data including line-of-sight acceleration and orbital precession, but find them to be implausible. The observed
period derivative implies a tidal quality factor
¢ = ´ -
+ Q 2.50 10 0.62
0.85 4, in good agreement with theoretical
predictions for inertial wave dissipation in subgiant stars. Additionally, while it probably cannot explain the entire
inspiral rate, a small amount of planetary dissipation could naturally explain the deep optical eclipse observed for
the planet via enhanced thermal emission. As the first evolved system with detected inspiral, Kepler-1658 is a new
benchmark for understanding tidal physics at the end of the planetary life cycle
Artigo descreve como os cientistas utilizaram o Telescópio Espacial Hubble para descobrir a estratosfera num exoplaneta classificado como um Júpiter quente. Descoberta essa que pode ajudar a descobrir como os exoplanetas se formam e qual a composição de suas atmosferas.
Uma equipe formada por astrônomos de Israel, da Europa, da Coreia e dos EUA, anunciou a descoberta de um exoplaneta gigante gasoso circumbinário, na zona habitável de seu par de estrelas, uma ocorrência surpreendentemente comum para os exoplanetas circumbinários descobertos pela missão Kepler/K2 da NASA.
Lembrando o planeta da ficção, Tatooine, exoplanetas circumbinários orbitam duas estrelas e assim têm dois sóis em seu céu.
O exoplaneta circumbinário, recém-descoberto, denominado de Kepler-453b, leva 240.5 dias para orbitar suas estrelas, enquanto as estrelas orbitam uma com relação a outra a cada 27.3 dias.
A estrela maior, a Kepler-453A, é similar ao nosso Sol, contendo 94% da massa do Sol, enquanto que a estrela menor, a Kepler-453B, tem cerca de 20% da massa e é mais fria e mais apagada.
O sistema binário, localiza-se na constelação de Lyra, e está a aproximadamente 1400 anos-luz de distância da Terra. Estima-se que esse sistema tenha entre 1 e 2 bilhões de anos de vida, sendo bem mais novo que o nosso Sistema Solar.
Também conhecido como KIC 9632895b, o Kepler-453b tem um raio 6.2 vezes maior que o da Terra. Sua massa não foi medida nos dados atuais, mas provavelmente ele deve ter cerca de 16 vezes a massa da Terra.
De acordo com os astrônomos, o Kepler-453b, é o terceiro planeta circumbinário da missão Kepler, descoberto na zona habitável de um par de estrelas.
Devido ao seu tamanho, e a sua natureza gasosa, o planeta pouco provavelmente deve abrigar a vida como nós a conhecemos. Contudo, ele pode, como os gigantes gasosos do Sistema Solar, ter grandes luas, e essas luas poderiam ser habitáveis. Sua órbita se manterá estável por 10 milhões de anos, aumentando a possibilidade da vida se formar nas suas luas.
Com o número de exoplanetas circumbinários conhecidos agora em dez, os cientistas podem começar a comparar diferentes sistemas e procurar uma tendência. Os sistemas tendem a ser bem compactos e podem aparecer num grande número de configurações.
Uma vez pensados como sendo raros e até mesmo impossíveis de existir, essa e outras descobertas do Kepler, confirmam que esses planetas são comuns na nossa Via Láctea.
“A diversidade e complexidade desses sistemas circumbinários é algo maravilhoso. Cada novo planeta circumbinário, é uma joia, revelando algo inesperado e desafiador”, disse o Prof. William Welsh da Universidade Estadual de San Diego, e o primeiro autor do artigo que descreve a descoberta, publicado no Astrophysical Journal.
Fonte:
http://www.sci-news.com/astronomy/science-kepler453b-circumbinary-exoplanet-03117.html
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
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.
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.
Deep Behavioral Phenotyping in Systems Neuroscience for Functional Atlasing a...Ana Luísa Pinho
Functional Magnetic Resonance Imaging (fMRI) provides means to characterize brain activations in response to behavior. However, cognitive neuroscience has been limited to group-level effects referring to the performance of specific tasks. To obtain the functional profile of elementary cognitive mechanisms, the combination of brain responses to many tasks is required. Yet, to date, both structural atlases and parcellation-based activations do not fully account for cognitive function and still present several limitations. Further, they do not adapt overall to individual characteristics. In this talk, I will give an account of deep-behavioral phenotyping strategies, namely data-driven methods in large task-fMRI datasets, to optimize functional brain-data collection and improve inference of effects-of-interest related to mental processes. Key to this approach is the employment of fast multi-functional paradigms rich on features that can be well parametrized and, consequently, facilitate the creation of psycho-physiological constructs to be modelled with imaging data. Particular emphasis will be given to music stimuli when studying high-order cognitive mechanisms, due to their ecological nature and quality to enable complex behavior compounded by discrete entities. I will also discuss how deep-behavioral phenotyping and individualized models applied to neuroimaging data can better account for the subject-specific organization of domain-general cognitive systems in the human brain. Finally, the accumulation of functional brain signatures brings the possibility to clarify relationships among tasks and create a univocal link between brain systems and mental functions through: (1) the development of ontologies proposing an organization of cognitive processes; and (2) brain-network taxonomies describing functional specialization. To this end, tools to improve commensurability in cognitive science are necessary, such as public repositories, ontology-based platforms and automated meta-analysis tools. I will thus discuss some brain-atlasing resources currently under development, and their applicability in cognitive as well as clinical neuroscience.
This presentation explores a brief idea about the structural and functional attributes of nucleotides, the structure and function of genetic materials along with the impact of UV rays and pH upon them.
T he effect_of_orbital_configuration)_on_the_possible_climates_and_habitability_of_kepler_62f
1. Research Article
The Effect of Orbital Configuration on the Possible
Climates and Habitability of Kepler-62f
Aomawa L. Shields,1,* Rory Barnes,2,* Eric Agol,2,*
Benjamin Charnay,2,* Cecilia Bitz,3,* and Victoria S. Meadows2,*
Abstract
As lower-mass stars often host multiple rocky planets, gravitational interactions among planets can have significant
effects on climate and habitability over long timescales. Here we explore a specific case, Kepler-62f (Borucki et al.,
2013), a potentially habitable planet in a five-planet system with a K2V host star. N-body integrations reveal the
stable range of initial eccentricities for Kepler-62f is 0.00 £ e £ 0.32, absent the effect of additional, undetected
planets. We simulate the tidal evolution of Kepler-62f in this range and find that, for certain assumptions, the planet
can be locked in a synchronous rotation state. Simulations using the 3-D Laboratoire de Me´te´orologie Dynamique
(LMD) Generic global climate model (GCM) indicate that the surface habitability of this planet is sensitive to
orbital configuration. With 3 bar of CO2 in its atmosphere, we find that Kepler-62f would only be warm enough for
surface liquid water at the upper limit of this eccentricity range, providing it has a high planetary obliquity
(between 60° and 90°). A climate similar to that of modern-day Earth is possible for the entire range of stable
eccentricities if atmospheric CO2 is increased to 5 bar levels. In a low-CO2 case (Earth-like levels), simulations
with version 4 of the Community Climate System Model (CCSM4) GCM and LMD Generic GCM indicate that
increases in planetary obliquity and orbital eccentricity coupled with an orbital configuration that places the
summer solstice at or near pericenter permit regions of the planet with above-freezing surface temperatures. This
may melt ice sheets formed during colder seasons. If Kepler-62f is synchronously rotating and has an ocean, CO2
levels above 3 bar would be required to distribute enough heat to the nightside of the planet to avoid atmospheric
freeze-out and permit a large enough region of open water at the planet’s substellar point to remain stable. Overall,
we find multiple plausible combinations of orbital and atmospheric properties that permit surface liquid water on
Kepler-62f. Key Words: Extrasolar planets—Habitability—Planetary environments. Astrobiology 16, xxx–xxx.
1. Introduction
NASA’s Kepler mission (Borucki et al., 2006), launched
in 2009, identified more than 4700 transiting planet
candidates—over 2300 of which have been confirmed as
planets—in its first 5 years of observations1
. Recent statistical
surveys estimate *40% of planetary candidates to be mem-
bers of multiple-planet systems (Rowe et al., 2014). Analyses
also suggest a low false-positive probability of discovery, in-
dicating that the clear majority of these multiple-planet can-
didates are indeed real, physically associated planets (Lissauer
et al., 2012b, 2014). Kepler data also indicate that smaller stars
are more likely to host a larger number of planets per star
(Swift et al., 2013), and smaller planets are more abundant
around smaller stars (Howard et al., 2012; Mulders et al.,
2015). These statistical data suggest that systems of multiple
small planets orbiting low-mass stars are a major new plane-
tary population, and one that may be teeming with habitable
worlds (Anglada-Escude´ et al., 2013).
One of the systems of particular interest for habitability
orbits Kepler-62 [Kepler Input Catalog (KIC) 9002278,
Kepler Object of Interest (KOI) 701], a K2V star. With a1
http://kepler.nasa.gov as of May 10, 2016
1
NSF Astronomy and Astrophysics Postdoctoral Fellow, UC President’s Postdoctoral Program Fellow, Department of Physics and
Astronomy, University of California, Los Angeles, and Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts.
2
Department of Astronomy and Astrobiology Program, University of Washington, Seattle, Washington.
3
Department of Atmospheric Sciences, University of Washington, Seattle, Washington.
*NASA Astrobiology Institute’s Virtual Planetary Laboratory.
ª Aomawa L. Shields, et al., 2016; Published by Mary Ann Liebert, Inc. This Open Access article is distributed under the terms of the
Creative Commons Attribution Noncommercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits any noncom-
mercial use, distribution, and reproduction in any medium, provided the original author(s) and the source are credited.
ASTROBIOLOGY
Volume 16, Number 6, 2016
Mary Ann Liebert, Inc.
DOI: 10.1089/ast.2015.1353
1
2. mass of 0.69 M1 and a radius of 0.63 R1, Kepler-62 hosts
five planets—Kepler-62b–f—with orbital periods ranging
from *5 to *267 days and radii from 0.54 to 1.95 R4
(Borucki et al., 2013). The inclinations of all five planets are
edge-on (i * 89–90°). However, neither their orbital ec-
centricities nor their planetary obliquities are constrained.
The two outermost planets, Kepler-62e (1.61 R4) and
Kepler-62f (1.41 R4) receive 120% and 41% of the amount
of flux that Earth receives from the Sun, respectively.
Kepler-62e, with an equilibrium temperature of *270 K
without an atmosphere, is likely to be too hot (with an at-
mosphere) to have liquid water on its surface, although a
significant amount of cloud cover could reflect incident ra-
diation and cool a planet, if it is synchronously rotating
(Yang et al., 2013, 2014). In contrast, Kepler-62f sits near
the outer edge of the habitable zone, with a relatively low
incoming stellar insolation (hereafter ‘‘instellation’’). How-
ever, the planet could avoid freezing with a sufficient
greenhouse effect (Kaltenegger et al., 2013), although there
are few measured planetary characteristics that could help
constrain whether habitability is likely.
Based on planet size and instellation, Kepler-62f is the
most likely candidate for a habitable world in this system.
While Kepler-62f has a radius of 1.41 R4 (Borucki et al.,
2013), its mass is unknown, leaving its density also un-
constrained. Recent statistical surveys of a population of
Kepler planets with known masses [from companion radial
velocity (RV) surveys] found that volatile inventory in-
creases with planet radius (Marcy et al., 2014; Weiss and
Marcy, 2014). However, the most recent Bayesian analysis
of Kepler planets with RV follow-up data found that planets
with radii £1.6 R4 are likely sufficiently dense to be rocky
(composed of iron and silicates), though this study was
limited to close-in planets with orbital periods less than
50 days (Rogers, 2015).
There are many planetary properties that affect the pres-
ence of surface liquid water and perhaps life, and in the
absence of sufficient observational data, many of the effects
of these properties can only be explored using a global
climate model (GCM). Previous work on the climate mod-
eling of Kepler-62f found that 1.6–5 bar of CO2 would yield
surface temperatures above the freezing point of liquid
water, depending on the mass and surface albedo of the
planet (Kaltenegger et al., 2013). However, this work was
done using a 1-D radiative-convective atmospheric code and
did not include a treatment of clouds beyond a scaling of
surface albedo. Additionally, the effect of the orbital ar-
chitecture and evolution of this multiple-planet system on
the climate of Kepler-62f was not explored. The eccentricity
of a planet could be pumped to high values in the presence
of additional companions in the system (Mardling, 2007;
Correia et al., 2012), and the eccentricity of Kepler-62f is
poorly constrained. The effect of different rotation rates on
atmospheric circulation was also not examined. Changes in
planetary obliquity (Ward, 1974; Williams, 1975; Williams
and Kasting, 1997; Dobrovolskis, 2013) and eccentricity
(Berger et al., 1993, 2006) will affect the seasonality and
average instellation received by a planet throughout its orbit,
respectively. Simulations have found that a large moon
around Kepler-62f could be long lived over timescales
necessary for biological evolution and could help stabilize
the planet’s obliquity and climate (Sasaki and Barnes,
2014), as the Moon has for Earth (Laskar et al., 1993).
However, large moons may not be required to stabilize a
planet’s obliquity over long timescales, given that varia-
tions in a planet’s obliquity without a moon would be
constrained (Lissauer et al., 2012a) and slowly evolving (Li
and Batygin, 2014). Large moons could even be detrimental
at the outer edge of the habitable zone (Armstrong et al.,
2014). Additionally, planetary rotation rate has been shown
to affect atmospheric circulation (Joshi et al., 1997; Merlis
and Schneider, 2010; Showman and Polvani, 2011; Show-
man et al., 2011, 2013). Quantifying the effect of orbital
and rotational dynamics on the climate of Kepler-62f using a
3-D GCM is therefore crucial for a more accurate assess-
ment of its habitability.
An understanding of the effect of tides on orbital evolu-
tion and planetary habitability is vital given the close
proximity of low-mass planets orbiting in the habitable
zones of their stars, and the likelihood of additional plane-
tary companions in these systems. Tides raised between a
star and a close orbiting planet introduce torques on the
planet, resulting in changes in semimajor axis and eccen-
tricity (Barnes et al., 2008, 2009). With an orbital period
of *267 days, tidal effects are expected to be weak but
could affect the rotation rate of the planet (Heller et al.,
2011). Recent work has shown that planets orbiting in the
habitable zones of lower-mass stars may not necessarily be
synchronously rotating (Leconte et al., 2015). Bolmont et al.
(2014, 2015) found it likely that the rotation period of
Kepler-62f is still evolving (and therefore not synchronized
with its orbital period) and that it could have a high obliquity.
However, they used only one tidal model, and others exist.
Here, we combine constraints obtained with an orbital
evolution model with a 3-D GCM to explore the effect of
orbital configuration on the climate and habitability of
Kepler-62f, for different atmospheric compositions and
planetary rotation rates. We calculated the orbital locations
of the inner four planets in the Kepler-62 system relative to
the position of Kepler-62f, for a range of possible initial
eccentricities and longitudes of pericenter for this planet.
We then used an n-body model to integrate the orbits of all
five planets given different planetary masses, to identify the
maximum initial eccentricity possible for Kepler-62f while
still maintaining stability within the planetary system. With
these results we calculated the rotational and obliquity
evolution possible for this planet. The potential habitability
as a function of its stable eccentricity was then explored
with a GCM, for atmospheres with Earth-like and high CO2
levels, focusing on the presence of surface liquid water on
the planet over an annual cycle.
2. Models
Here we describe the orbital and climate models used for
this study. The existing n-body model HNBody (Section
2.1) is used to integrate the orbits of multiple planets in a
system orbiting a central, dominant body (in this case a
star). Our method for estimating the masses for the planets is
described in Section 2.2. In Section 2.3 we describe the
models used to explore the tidal evolution of Kepler-62f.
The two GCMs used to run climate simulations of the po-
tentially habitable planet Kepler-62f (with output from the
n-body model as input) are described in Section 2.4.
2 SHIELDS ET AL.
3. 2.1. HNBody: Modeling the orbital evolution
of multiple-planet systems
The Hierarchical N-Body (HNBody) package (Rauch and
Hamilton, 2002), a set of software utilities we employed as
our n-body model, integrates the orbits of astronomical
bodies governed by a dominant central mass. It is based on
the technique of symplectic integration, an n-body mapping
method, developed by Wisdom and Holman (1991), and
performs standard point mass orbital integrations for a given
number of planets in a system.
In the n-body mapping method, the Hamiltonian—a
mathematical function used to generate the equations of
motion for a dynamical system—is the sum of the Keplerian
and the interacting contributions to the motion of orbiting
planetary bodies (Wisdom and Holman, 1991). The former
describes the Keplerian motion of the orbiting planetary
bodies around a central mass (the host star), and the latter
describes the gravitational interactions between the planets
themselves.
The evolution of the complete Hamiltonian is determined
by alternately evolving the Keplerian and interacting parts
separately in a sequence of steps leading to new n-body
maps of the system, which are composed of the individual
Keplerian evolution of the planets and the kicks due to the
perturbations the planets deliver to one another. The output
from HNBody consists of a series of data files that describe
the evolution of selected orbital parameters over time. In the
next section we describe the inputs that HNBody requires to
generate this information.
2.1.1. HNBody: Model inputs. While we know from
transit timing data where each planet in the Kepler-62 sys-
tem is relative to our line of sight when it transits its host
star, the locations of the other four planets at each planet’s
individual transit time are unconstrained. An accurate inte-
gration of their orbits requires the location of all planets at
the same epoch.
The Keplerian orbit of a planetary body can generally be
described by a set of six parameters that characterize the
orbit. The parameters we chose as input to HNBody for each
of the five planets in the Kepler-62 system were the semi-
major axis a, the orbital eccentricity e, the inclination of the
orbit i, the longitude of the ascending node U, the longitude
of pericenter x, and the true anomaly f (see Fig. 1 and
Table 1 for definitions of these parameters).
While a and i are constrained from transit observations of
the Kepler-62 system (Borucki et al., 2013), e, U, x, and f
are poorly constrained. Given the close proximities of
planets 62b–e (0.05–0.43 AU), which are all within their
tidal circularization orbital radii after 4.5 Gyr (Kasting et al.,
1993), and the estimated age of Kepler-62 (*7 billion
years, Borucki et al., 2013), we assumed e = 0 for these inner
four planets. However, we acknowledge that in a multiple-
planet system, the tidal evolution of a close-in planet is
coupled to secular interactions with other planets in the
system, and these interactions can cause planet eccentricities
to vary (Greenberg and Van Laerhoven, 2011; Laskar et al.,
2012; Hansen and Murray, 2015).
Following from this assumption, x is undefined, as all
points along the orbit are equidistant from the star. We also
assumed U = 0 for all planets. This is reasonable given that
i * 89–90° for all planets, thus constituting an edge-on orbit
capable of yielding a transit observable by Earth. We de-
termined the locations of Kepler-62b–e relative to Kepler-
62f at the same point in time, assuming a range of possible
eccentricities between 0.0 and 0.9 and a range of longitudes
of pericenter o between 0 and 2p for Kepler-62f. In the
Appendix we outline the equations that were used to gen-
erate the locations of all planets in the system, using transit
data for these planets (Borucki et al., 2013), and the
aforementioned values for the other orbital elements.
2.2. Planetary masses of the Kepler-62 system
HNBody also requires a seventh parameter as input—the
planet’s mass relative to its host star. There are several
mass-radius relations in the literature, and we chose two to
explore the effect of planetary mass on the orbital evolution
of the Kepler-62 system. We used the following mass-radius
relation determined by Kopparapu et al. (2014) derived
from the exoplanets.org database (Wright et al., 2011):
Mp
MÈ
¼ 0:968
Rp
RÈ
3:2
, Mp 5MÈ (1)
This yields a planetary mass of *3 M4 for Kepler-62f.
We also ran HNBody integrations with planet masses de-
rived using the following mass-radius (for Kepler-62d, e,
and f) and density r (for Kepler-62b and c) relations from
Weiss and Marcy (2014):
Mp
MÈ
¼ 2:69
Rp
RÈ
0:93
, 1:5
Rp
RÈ
4 (gaseous) (2)
q ¼ 2:43 þ 3:39
Rp
RÈ
g=cm3
, Rp 1:5RÈ (rocky) (3)
The Weiss and Marcy (2014) relationship resulted in higher
masses for Kepler-62b and f and lower masses for Kepler-
62c, d, and e, compared to those using the Kopparapu et al.
(2014) treatment. Finally, we ran additional orbit integrations
FIG. 1. Geometry of the elliptical orbit of a body of mass
m2 around m1. The ellipse has semimajor axis a, semiminor
axis b, eccentricity e, and longitude of pericenter x. The true
anomaly f denotes the angle subtended by an imaginary line
connecting m1 with the location of m2 in its orbit and one
connecting m1 with pericenter (the point of closest approach
to m1). This assumes that m1 m2.
EFFECT OF ORBITAL CONFIGURATION ON KEPLER-62F 3
4. with the maximum mass limits for all planets, as determined
by Borucki et al. (2013). Although these maximum masses
are likely unphysical, they should result in a similar constraint
on eccentricity as more physically plausible mass estimates
(such as iron or Earth-like compositions). This varied ap-
proach allows us to address the spread in mass-radius rela-
tionships that can arise given different planetary compositions
(Wolfgang and Lopez, 2015). The masses for all five Kepler-
62 planets used as input to HNBody integrations are given in
Table 2.
Additional model specifications include the preferred co-
ordinate system, the class of particles (based on the scale of
the masses and how their interaction is to be taken into ac-
count), and the time step and total length of integration. We
specified a bodycentric coordinate system (ex. heliocentric
reference frame in the case of the Solar System), which treats
the system as dominated by the mass of the central star. We
ran our HNBody integrations for interactions between ‘‘heavy
weight particles’’ (which includes the star and the planets) for
106
years, with a time step equal to 1/20th and 1/100th of the
orbital period of the innermost planet in the Kepler-62 sys-
tem. As Kepler-62b has an orbital period of 5.7 days, we used
time steps of 0.29 and 0.06 days, respectively. See Deitrick
et al. (2015) for more details on HNBody. Barnes and Quinn
(2004) showed that in simulations that last one million orbits,
only *1% of ejections occurred in the timescale between 105
and 106
years of simulation, with the vast majority of unstable
configurations occurring within 104
years. While orbital in-
stabilities can arise at any timescale, one million orbital pe-
riods has emerged as a practical reference.
We defined orbital stability as a successful integration in
which stable, periodic amplitude oscillation was present for
all planets throughout the entire million years, the energy
was conserved to better than one part in 104
, and no planets
were ejected from the system. Eccentricities spanning the
full range of stability for Kepler-62f were then used as input
to our GCMs. We then ran climate simulations of this planet
with a variety of atmospheric compositions, orbital config-
urations, and rotation rates to explore and assess its possible
climate states and to determine the best possible combina-
tion of these parameters for surface habitability.
2.3. Tidal model
In this section we consider the tidal evolution of Kepler-
62f. Bolmont et al. (2014, 2015) examined the rotational
evolution of planets e and f and found that the rotation
period of f is not synchronized with the orbital period and
that a wide range of obliquities is possible. However, they
only considered circular orbits for planet f. Furthermore,
they used only one equilibrium tide model in which the time
interval between the passage of the perturber and the pas-
sage of the tidal bulge is constant, a model we call the
constant time lag (CTL) model (Hut, 1981; Ferraz-Mello
et al., 2008; Leconte et al., 2010). In this section we relax
some of these choices and find that synchronous rotation of
Kepler-62f is possible.
In addition to the CTL model, we also employed a model
in which the angle between the perturber and the tidal bulge,
as measured from the center of the planet, is constant, a
model we call the constant phase lag (CPL) model (Goldreich
and Soter, 1966; Ferraz-Mello et al., 2008; Heller et al.,
2011). These two equilibrium tide models are mathematical
treatments of tidal deformation, angular momentum transfer,
Table 1. Orbital Elements Used to Describe Kepler-62 Planetary Orbits
Parameters Definition
Initial Values (Kepler-62b,
62c, 62d, 62e, 62f)
Semimajor
axis a (AU)
Half the longest diameter of an orbit 0.0553, 0.0929,
0.120, 0.427, 0.718
Eccentricity e The degree of ellipticity (oval shape) of an orbit (e = 0, circular; e = 1,
parabolic)
0.0, 0.0, 0.0,
0.0, 0.0–0.9
Inclination i (°) The angle between the planet’s orbital plane and the sky plane 89.2, 89.7, 89.7,
89.98, 89.90
Longitude of
ascending
node U
The angle between the sky plane’s 0° longitude and the point where the
planet passes from in front of to behind the star
0.0, 0.0, 0.0, 0.0, 0.0
Longitude of
pericenter x
The angle between a reference direction and the point of closest approach
of a planet to its star (pericenter)
0.0, 0.0, 0.0, 0.0,
0.0 / 2p (Dx = p/6)
True anomaly f The angle between a radius vector through pericenter and the planet’s
location on an orbital ellipse around its host star
Calculated in the Appendix
Angles here are in radians except for the orbital inclination, which is listed in degrees. In exoplanet geometry, i = 90° constitutes an edge-
on orbit capable of yielding a transit observable by Earth. Data for the semimajor axis and the orbital inclination are from Borucki et al.
(2013), though we have omitted the uncertainties here for ease of reading.
Table 2. Masses (M4) Used as Inputs to HNBody for Different Sets
of Orbital Integrations of the Planets Kepler-62b–f
Kepler-62b Kepler-62c Kepler-62d Kepler-62e Kepler-62f Relation/Source
2.3 0.1 8.2 4.4 2.9 Kopparapu et al. (2014)
2.8 0.1 5.0 4.2 3.7 Weiss and Marcy (2014)
9.0 4.0 14 36 35 Borucki et al. (2013)
4 SHIELDS ET AL.
5. and energy dissipation due to tidal friction, and both have
known flaws (Greenberg, 2009; Efroimsky and Makarov,
2013). However, they provide a qualitative picture of tidal
evolution and can be used to infer possible rotation states of
Kepler-62f.
Both models are one-dimensional with the tidal properties
encapsulated in either the time lag s for CTL or the tidal
quality factor Q for CPL. For both models we assumed that
Kepler-62f has the same tidal properties as Earth: s4 = 640 s
(Lambeck, 1977) and Q4 = 12 (Yoder, 1995). The values for
Kepler-62f are assuredly different, but these choices are
likely not off by more than an order of magnitude, assuming
Kepler-62f has oceans and continents. A Q of 100 would
result in a tidal locking timescale that is less than 10 times
longer.
Rather than present the full set of equations, the reader is
referred to Appendix E of Barnes et al. (2013). The salient
features are that each model contains six coupled differen-
tial equations that track the orbital semimajor axis and ec-
centricity, as well as the rotation rate and obliquity of both
bodies. The effects of the other planets in the system are
ignored. Therefore, we consider limiting cases to explore the
range of these effects. The equations conserve angular
momentum, and energy is dissipated by the tidal deforma-
tion of the bodies. In this case, tidal effects on the star are
negligible.
We used calculated minimum and maximum initial ec-
centricities for Kepler-62f (Section 3); initial spin periods of
8 h, 1 day, or 10 days; and initial obliquities of 5°, 23.5°, or
80°. We chose this range of initial conditions for Kepler-62f
with the goal of setting boundary conditions for the climate
simulations.
2.4. Climate modeling of Kepler-62f
Our primary goal in the climate modeling of Kepler-62f
was to identify the most favorable combination of planetary
parameters that would result in areas of the planet with
warm enough surface temperatures for liquid water. To
determine the scenario for which the largest habitable sur-
face area is possible, we varied the atmospheric composi-
tion, orbital eccentricity, planetary obliquity, the angle of
the vernal equinox (the point in the planet’s orbit where both
hemispheres receive equal instellation) relative to pericenter
(closest approach to the star), and the rotation rate of the
planet in our GCM simulations.
2.4.1. Model inputs to CCSM4. We used version 4 of the
Community Climate System Model (CCSM42
), a fully-
coupled, global climate model (Gent et al., 2011). We ran
CCSM4 with a 50 m deep slab ocean (see, e.g., Bitz et al.,
2012), with the ocean heat transport set to zero, as done in
experiments by Poulsen et al. (2001) and Pierrehumbert
et al. (2011). The ocean is treated as static but fully mixed
with depth. The horizontal resolution is 2°. There is no land,
hence we refer to it as an ‘‘aqua planet.’’ The sea ice
component to CCSM4 is the Los Alamos sea ice model
CICE version 4 (Hunke and Lipscomb, 2008). We made the
ice thermodynamic only (no sea-ice dynamics) and use the
more easily manipulated sea-ice albedo parameterization
from CCSM3, with the surface albedo divided into two
bands, visible (k £ 0.7 lm) and near-IR (k 0.7 lm). We
used the default near-IR and visible band albedos (0.3 and
0.67 for cold bare ice and 0.68 and 0.8 for cold dry snow,
respectively). For more details, see Shields et al. (2013).
Because CCSM does not easily allow a 267-day orbital
period (the actual orbital period of Kepler-62f), the orbital
period was set to 365 days, so the model would still simulate
a full annual cycle. As atmospheric radiative and convective
adjustment timescales are short compared to either orbital
period, we do not expect this to make much difference in the
overall climate. We used CCSM4 for continuity with our
previous work, to evaluate the general climate behavior
given changes in orbital parameters, and used the Labor-
atoire de Me´te´orologie Dynamique (LMD) Generic GCM to
simulate the climate of a planet with physical characteristics
more closely like those of Kepler-62f. The details of LMD
Generic GCM are given in the following section.
Kepler-62f receives 41% of the modern solar constant from
its star, therefore significant amounts of CO2 or other
greenhouse gases may be required to keep temperatures
above the freezing point of water on the surface, as is widely
assumed for planets near the outer edge of their host stars’
habitable zones (Kasting et al., 1993). An active carbon cycle
capable of generating increased amounts of atmospheric CO2
in response to decreasing surface temperatures (Walker et al.,
1981) would be a relatively straightforward means of main-
taining habitable surface temperatures on the planet. More
than *2 bar of CO2 could accumulate in the atmosphere of a
planet with an active carbon cycle before the maximum
greenhouse limit for CO2 is reached (Pierrehumbert, 2010).
Large increases in atmospheric CO2 concentration begin to
have significant effects on convection and the manner in
which it adjusts the temperature lapse rate (the rate at which
atmospheric temperature decreases with increasing altitude)
on a planet. Additionally, CO2 condensation becomes likely
at levels of 1–2 bar, and collisional line broadening becomes
important, increasing the infrared opacity of the atmosphere
(Pierrehumbert, 2005). These effects are neglected in Earth-
oriented GCMs such as CCSM4. We therefore used the
CCSM4 model to simulate only scenarios with an Earth-like
atmospheric CO2 concentration (400ppmv) and allowed
water vapor to vary throughout each simulation according to
evaporation and precipitation processes. The rest of the at-
mospheric composition is preindustrial. We then used an
additional GCM—LMD Generic GCM—to simulate the cli-
mate of Kepler-62f with Earth-like as well as 1–12 bar of
CO2, as LMD Generic GCM contains parameterizations for
addressing atmospheres with high CO2 content.
It was important to consider the possibility that Kepler-
62f may not have sufficient atmospheric CO2 to keep sur-
face temperatures above freezing. We therefore explored
alternate means of creating habitable areas of the planet with
lower, Earth-like CO2 levels. Given the effects of planetary
obliquity (Ward, 1974; Williams, 1975) and eccentricity
(Berger et al., 1993, 2006) on seasonality and annual global
instellation, the best possible scenario for habitability in the
2
We used three components of CCSM4 in this work: CICE4,
CAM4, and a slab ocean. For simplicity, we refer collectively to this
suite of model components as CCSM4 throughout this work, as
done in Shields et al. (2013, 2014). Bitz et al. (2012)—the first
study to use the CCSM4 slab configuration—also used this con-
vention.
EFFECT OF ORBITAL CONFIGURATION ON KEPLER-62F 5
6. low-CO2 case may be one in which Kepler-62f has a high
obliquity and a high eccentricity. Additionally, an orbital
configuration in which the hotter, summer months in a given
hemisphere coincide with the pericenter of the planet’s orbit
could amplify the effects of high obliquity and eccentricity.
To test this prediction, we ran simulations with CCSM4 (and
LMD Generic GCM), assuming an aqua planet, with a range
of different values for these parameters.
We ran 30-year GCM simulations using CCSM4 with the
input maximum initial eccentricity for stable HNBody in-
tegrations for Kepler-62f (see Section 3). We also ran ad-
ditional simulations with lower eccentricity values to
explore the effect of eccentricity on instellation and plane-
tary surface temperature. We used a synthetic stellar spec-
trum from the Pickles Stellar Atlas (Pickles, 1998), with flux
in the range of 1150–25000 A˚ , and an effective photospheric
temperature of 4887 K, which is close to the estimated ef-
fective temperature of Kepler-62 (4925 K, Borucki et al.,
2013). The percentage of the total flux from the star was
specified in each of the 12 incident wavelength bands in
CAM4 (see Table 3), as done in Shields et al. (2013, 2014).
We also ran 40-year CCSM4 simulations with an Earth-
like obliquity of 23°, and with an obliquity of 60°. To
explore the influence of the location of summer solstice
relative to pericenter, we varied the angle of the vernal
equinox relative to the longitude of pericenter (VEP), which
governs the difference in instellation between southern
hemisphere summer and northern hemisphere summer
(Fig. 13). Because CCSM4 is parameterized for Earth-like
conditions, we kept the radius, mass, and surface gravity of
the planet equal to those of Earth in these simulations.
2.4.2. LMD generic GCM. We used the Laboratoire de
Me´te´orologie Dynamique (LMD) Generic GCM (Hourdin
et al., 2006), developed to simulate a wide range of planetary
atmospheres and climates. It has been used in studies of the
early climates of Solar System planets (Charnay et al., 2013;
Forget et al., 2013; Wordsworth et al., 2013) and in previous
studies of the climates of extrasolar planets (Wordsworth
et al., 2011; Leconte et al., 2013; Wordsworth, 2015).
Like CCSM4, LMD Generic GCM solves the primitive
equations of fluid dynamics using a finite difference method
and a 3-D dynamical core. The radiative transfer scheme is
based on a correlated-k method, with absorption coefficients
calculated from high-resolution spectra generated using the
HITRAN 2008 database (Rothman et al., 2009). A smaller
database of correlated-k coefficients was then generated
from this spectra using 12· 9 · 8 temperature (T = 100, 150,
., 600, 650 K, in 50 K steps), log-pressure ( p = 0.1, 1,
10, ., 107
Pa), and water vapor mixing ratio (qH2O = 10-7
,
10-6
, ., 1) grids. These correlated-k coefficients ensure ex-
pedient radiative transfer calculations in the GCM. The
spectral intervals included 38 shortwave (incident stellar ra-
diation) bands and 36 longwave (outgoing radiation) bands,
with a 16-point cumulative distribution function for integra-
tion of absorption data within each band. The radiative
transfer equation is then solved in each atmospheric layer
using a two-stream approximation (Toon et al., 1989). Para-
meterizations for convective adjustment, and CO2 collision-
induced absorption, are included based on work by Words-
worth et al. (2010). Simulations were run with a two-layer
ocean, including a 50m deep top layer and an underlying
150 m deep second layer. Both layers are assumed to be well
mixed, with horizontal diffusion used to approximate ocean
heat transport by large-scale eddies. Adiabatic adjustment is
also included, whereby the ocean lapse rate is adjusted to
maintain a warmer top ocean layer at all times.
We ran our LMD Generic GCM simulations for 60–200
years (depending on the amount of CO2 and required model
equilibration time) with a horizontal spatial resolution of
64 · 48 (corresponding to 5.625° longitude · 3.75° latitude),
with 20 vertical levels. A blackbody spectrum with the
stellar effective temperature of Kepler-62 (4925 K, Borucki
et al., 2013) was used as the host star spectrum. The albedo
of snow was set to 0.55 for the high-CO2 simulations and
0.43 for the simulations with Earth-like CO2 (to match the
two-band albedo parameterization in CCSM4 for accurate
comparison). The albedo of sea ice was allowed to vary
between a minimum of 0.20 and a maximum of 0.65, de-
pending on ice thickness. We assumed an aqua planet with
different amounts of atmospheric CO2, and water vapor that
varied throughout each simulation as with CCSM4. We used
the radius of Kepler-62f (1.41 R4, Borucki et al., 2013), a
surface gravity of 14.3 m/s2
, based on a *3 M4 planet (see
Section 2.2), a 267-day year, Earth-like (24 h) and syn-
chronous (267-day) rotation rates, and the minimum and
maximum stable initial eccentricities possible for Kepler-
62f (see Section 3). Additional input parameters for simu-
lations using CCSM4 and LMD Generic GCM for our work
on Kepler-62f are given in Tables 4 and 5. The results of
these simulations and the implications for the habitability of
Kepler-62f are presented and discussed in the following
section.
3. Results
3.1. N-body simulations
Figure 2 shows the fraction of stable orbital integrations
performed using HNBody, assuming different initial ec-
centricities for Kepler-62f and zero eccentricity for Kepler-
62b–e (see e.g., Barnes and Quinn, 2001). The maximum
initial eccentricity for which stable integrations were
Table 3. CAM4 Spectral Wavelength Bands
Specifying Shortwave (Stellar) Incoming Flux
into the Atmosphere, and the Percentage of Flux
within Each Waveband for a Synthetic Spectrum
of a K Dwarf Star with a Similar Photospheric
Temperature to Kepler-62, from the Pickles
Stellar Atlas (Pickles, 1998)
Band lmin lmax K2V star % flux
1 0.200 0.245 0.128
2 0.245 0.265 0.075
3 0.265 0.275 0.054
4 0.275 0.285 0.056
5 0.285 0.295 0.070
6 0.295 0.305 0.091
7 0.305 0.350 1.076
8 0.350 0.640 27.33
9 0.640 0.700 6.831
10 0.700 5.000 64.35
11 2.630 2.860 0.000
12 4.160 4.550 0.000
6 SHIELDS ET AL.
7. possible for greater than 90% of the simulated longitudes of
pericenter was e = 0.32, assuming the Kopparapu et al.
(2014) mass-radius relation. A higher upper eccentricity
limit is 0.36 assuming a smaller mass (equal to that of Earth)
for Kepler-62f and a larger mass for Kepler-62e. Simula-
tions using a shorter time step of 1/100th of the orbital
period of the innermost planet reduced the percentage of
longitudes of pericenter with stable integrations at e = 0.32
by *30%, though we still found over half of our simulated
configurations at this eccentricity to be stable. Stable inte-
grations were possible for 23% of the simulated longitudes
of pericenter at e = 0.33. However, we did not consider this a
large enough fraction of stable configurations, and consider
e = 0.32 to be the conservative maximum. The maximum
stable initial eccentricity decreased by *3%, to e = 0.31,
when the Weiss and Marcy (2014) mass-radius and density
relations were used, and decreased by 28%, to e = 0.23,
using the maximum mass limits for all planets (Borucki
et al., 2013). The evolution of the eccentricities of all five
planets for a stable integration at e = 0.32 for Kepler-62f is
shown in Fig. 3. All planets exhibited eccentricity oscilla-
tions—a characteristic of multiple-planet systems—with a
regular period that remained constant over the entire 106
-
year integration. Integrations assuming higher initial ec-
centricities for Kepler-62f yielded eccentricity evolution
that exhibited irregular oscillatory motion indicative of the
occurrence of significant orbital shifts. Consequently, we
considered 0.00 £ e £ 0.32 to be the maximum allowable
range of initial eccentricities for Kepler-62f.
3.2. Tidal evolution of Kepler-62f
We began our simulations with e = 0.00 or 0.32 and spin
periods and obliquities as given in Section 2.3. In general,
tidal evolution is faster for larger eccentricity, larger spin
period, and smaller obliquity. Thus the e = 0.32, 10-day spin
period and 5° obliquity cases should evolve most rapidly
toward an equilibrium spin state.
In Fig. 4 we show the evolution of spin period and
obliquity for the two tidal models. The difference between
the two models naturally produces different torques on the
planetary rotation and thus different timescales to reach
equilibrium. On the left, the CTL model shows results very
similar to those in Bolmont et al. (2014, 2015), and it is
unlikely that the system has reached a tidally locked state,
though tidal de-spinning is significant over 10 Gyr. The right
panels show that tidal locking is possible, which is easily
shown by the spin period evolution flattening out at either
267 or 178 days. The latter corresponds to a 2:3 spin-orbit
resonance, which is closer to the equilibrium spin period for
an eccentricity of 0.32. Only the extremely fast-rotating and
high-obliquity cases do not tidally lock within 5 Gyr in the
CPL model.
As the estimated age of Kepler-62 (7 Gyr, Borucki et al.,
2013) is uncertain, as well as the initial eccentricity and
rotation state, we conclude that the rotational period of
Kepler-62f can lie anywhere from less than 1 day all the
way to 267 days. Similarly, the obliquity can have a range of
values from 0 to at least 90°. For our assumptions, the ro-
tation period and obliquity should lie between the solid gray
line and the dotted black line. Therefore, habitability and
climate studies of this planet should account for this range
of rotational states, as well as both small and large obliq-
uities. We present the results of such studies in the following
section.
3.3. Climate simulations
With the present atmospheric level (PAL) of CO2 on
Earth (400 ppmv), all CCSM4 simulations with eccentricity
e = 0.00–0.32 resulted in completely ice-covered conditions,
with global mean surface temperatures below 190 K. While
our CCSM4 simulations were run with a 365-day orbital
period rather than the actual orbital period of Kepler-62f
(267 days), a comparison of LMD Generic GCM sensitivity
tests run with 267- and 365-day orbital periods showed
Table 4. Additional Input Parameters Used in CCSM4 Climate Simulations of Kepler-62f
Parameter Run1 Run2 Run3 Run4 Run5 Run6 Run7
Orbital eccentricity 0.0 0.1 0.2 0.32 0.32 0.32 0.0
Obliquity (°) 23 23 23 23 60 23 0
Rotation rate 24 h 24 h 24 h 24 h 24 h 24 h 365 days
VEP (°) 90 90 90 90 90 0 90
Here the parameter ‘‘VEP’’ is the angle of the vernal equinox relative to pericenter. Run7 is the synchronous rotation rate case, where the
planet’s rotation period is equal to its orbital period.
Table 5. Additional Input Parameters Used in High-CO2 LMD Generic GCM
Climate Simulations of Kepler-62f
Parameter Run1 Run2 Run3 Run4 Run5 Run6 Run7 Run8 Run9 Run10 Run11 Run12–27
Ecc 0.32 0.00 0.32 0.32 0.32 0.32 0.32 0.00 0.00 0.00 0.00 0–0.32
Obl (°) 23.5 23.5 23.5 23.5 23.5 23.5 23.5 0.00 0.00 0.00 0.00 0–90
CO2 (bar) 1 3 3 5 8 10 12 1 1 3 3 3
Rot 24 h 24 h 24 h 24 h 24 h 24 h 24 h 24 h 267 days 24 h 267 days 24 h
VEP 0 0 0 0 0 0 0 0 0 0 0 0–90
Two additional simulations were run with Earth-like CO2, obliquities of 23° and 60°, e = 0.32 and a VEP of 90°, for comparison with the
CCSM4 simulations. Both sets of simulations are shown in Fig. 12.
EFFECT OF ORBITAL CONFIGURATION ON KEPLER-62F 7
8. equivalent results. Figure 5 shows the annual mean in-
stellation as a function of latitude for these different ec-
centricities, assuming an obliquity of 23°. The average
instellation over an annual cycle increases with eccentricity
(Berger et al., 1993, 2006; Williams and Pollard, 2002), in
accordance with the following relation:
S ¼
Sa
ffiffiffiffiffiffiffiffiffiffiffiffi
1 À e2
p (4)
where S is the average instellation at the mean star-planet
distance; Sa is the instellation at a given distance a from the
star during a planet’s orbit; and e is the eccentricity of the
planet’s orbit (Berger et al., 2006).
If CO2 is efficiently outgassed, and the silicate weathering
rate is weak, higher levels of CO2 may be expected to ac-
cumulate in the planet’s atmosphere prior to reaching the
maximum greenhouse limit (Kopparapu et al., 2013a,
2013b). Since PAL CO2 was clearly insufficient to yield
habitable surface temperatures for Kepler-62f at its value of
incoming stellar flux, we ran simulations using LMD Gen-
eric GCM with CO2 concentrations of up to 12 bar, at both
limits of the stable eccentricity range for Kepler-62f. We let
the amount of water vapor vary (through transport, evapo-
ration, and circulation) during the course of each simulation.
Global mean, minimum, and maximum surface tempera-
tures for each simulation are plotted in Fig. 6. With 5 bar of
CO2 in the atmosphere, Kepler-62f exhibits a global mean
surface temperature similar to modern Earth, at *282
and *290 K for the lower and upper stable eccentricity
limits, respectively. Surface temperatures increase with CO2
concentration. However, while the surface temperature on
the planet is 46–50 K warmer (depending on eccentricity)
with 5 bar of atmospheric CO2 compared to the 3 bar CO2
FIG. 2. Fraction of stable configurations
after a 106
-year HNBody integration for
initial eccentricities between 0.0 and 0.9 for
Kepler-62f, assuming the Kopparapu et al.
(2014) mass-radius relationship. The eccen-
tricities of all other planets in the Kepler-62
system were set to zero.
e_f=0.320, omega=3.14
0 2•105
4•105
6•105
8•105
1•106
Time (years)
0.0
0.1
0.2
0.3
0.4
0.5
Eccentricity
b
c
d
e
f
FIG. 3. Evolution of the eccentricities of
Kepler-62b–f as a function of time calcu-
lated with HNBody. Initial eccentricities and
longitudes of pericenter for Kepler-62b–e
were set to zero. The initial eccentricity of
Kepler-62f was set to 0.32 with a longitude
of pericenter equal to p.
8 SHIELDS ET AL.
9. Constant Time Lag
0.1
1.0
10.0
100.0
SpinPeriod(d)
0 2 4 6 8 10
Time (Gyr)
50
100
150
Obliquity(∞)
Constant Phase Lag
0.1
1.0
10.0
100.0
SpinPeriod(d)
0 2 4 6 8 10
Time (Gyr)
50
100
150
Obliquity(∞)
a b
FIG. 4. Rotational evolution of Kepler-62f due to tidal processes. Left: Evolution of the spin period (top) and obliquity
(bottom) for the CTL model. The gray curves assume a circular orbit, and the black curves assume an eccentricity of 0.32.
Solid lines represent planets that begin with an 8 h rotation period and an obliquity of 80°. Dashed lines assume the planet
began with modern Earth’s rotational state. Dotted lines assume an initial spin period of 10 days and an obliquity of 5°.
Right: Same as left panels, but for the CPL model.
−100 −50 0 50 100
60
80
100
120
140
160
180
200
Latitude (∞)
Instellation(W/m2
)
e=0.0
e=0.1
e=0.2
e=0.3
FIG. 5. Instellation as a function of latitude
for Kepler-62f (using CCSM4), assuming
e = 0.0 (black), e = 0.1 (blue), e = 0.2 (green),
and e = 0.32 (red). The plots show 12-month
averages. The obliquity of the planet was set
to 23°. The angle of the vernal equinox rel-
ative to pericenter was set to 90°, similar to
that of Earth (102.7°). The larger the eccen-
tricity, the larger the annually averaged in-
stellation received at a given latitude.
EFFECT OF ORBITAL CONFIGURATION ON KEPLER-62F 9
10. case, it is only an additional 20–25 K warmer (*308 K)
with 8 bar of CO2 in the atmosphere. Further increases in
atmospheric CO2 yield successively smaller increases in
surface temperature. We also found that the planetary al-
bedo reached a minimum at 8 bar and then began to slowly
increase (Fig. 7). This indicates that we are likely ap-
proaching the point where the effects of Rayleigh scattering
begin to dominate over the greenhouse effect at this level of
CO2. Additionally, the difference between minimum and
maximum surface temperatures decreases with CO2 con-
centration, highlighting the role of a denser atmosphere in
evening out temperature contrasts (Pierrehumbert, 2011;
Wordsworth et al., 2011).
While the majority of our simulations run with 3 bar of
CO2, including that run at Earth’s present obliquity, yielded
globally ice-covered conditions (Fig. 8), we did find that at
an extremely high planetary obliquity (90°), at the upper
eccentricity limit (0.32), surface temperatures exceeded the
freezing point of water over close to 20% of the planet,
though the global mean surface temperature was well below
freezing, at 246 K. As shown in Fig. 8, the regions with zero
ice cover occur in the polar regions, which receive more
instellation than the equator at high obliquities. We also
found that, while high-eccentricity simulations with an
obliquity of 60° ultimately yielded ice-covered conditions,
maximum surface temperatures reached 273 K during the
planet’s orbit at small orbital distances from its star, which
could result in melting of ice formed when the planet is at
more distant points in its orbit.
Figure 9 shows the surface temperature as a function of
latitude and longitude for an LMD Generic GCM simulation
with 5 bar of CO2, variable water vapor, and e = 0.00. With a
global mean surface temperature of 282 K, only *17%
of the planet is ice-covered. Simulations run at e = 0.32 re-
sulted in a higher global mean surface temperature by *8 K,
and *10% less ice cover on the planet.
Given that Kepler-62f could have a wide range of rotation
periods, including a synchronous rotation rate, using
CCSM4 and LMD Generic GCM we ran simulations of the
planet assuming an Earth-like rotation rate, and a synchro-
nous rotation period, for 400 ppmv (Earth-like), 1 bar, and 3
bar CO2 atmospheres, with both the eccentricity and
obliquity set to zero. Our CCSM4 simulations with Earth-
like CO2 levels were completely ice covered. Figure 10
1 10
Bars CO2
200
250
300
350SurfaceTemperature(K)
Max
Min
Mean
FIG. 6. Mean (plus symbols), minimum (tri-
angles), and maximum (diamonds) surface
temperature for Kepler-62f after 100- to 200-
year LMD Generic GCM simulations, assum-
ing e = 0.00 (blue) and e = 0.32 (red), an Earth-
like rotation rate, and different levels of
atmospheric CO2. The mean values take into
account the location of measured surface tem-
perature values relative to the total surface area
of the planet. An obliquity of 23.5° and
VEP = 0° are assumed.
2 4 6 8 10 12 14
Bars CO2
0.332
0.334
0.336
0.338
0.340
0.342
PlanetaryAlbedo
FIG. 7. Planetary albedo of Kepler-62f as
a function of simulated atmospheric CO2
concentration after 100- to 200-year LMD
Generic GCM simulations. The 3 bar CO2
simulation, which was ice-covered, with a
planetary albedo of 0.491, is not shown, to
enlarge the turning point in planetary albedo at
8 bar CO2. An obliquity of 23.5°, an eccen-
tricity of zero, and VEP = 0° are assumed.
10 SHIELDS ET AL.
11. shows the surface temperature as a function of latitude and
longitude for the LMD Generic GCM 1 bar and 3 bar CO2
cases. The synchronous case with 1 bar of CO2 has a global
mean surface temperature of *206 K, with 99.7% of the
planet covered in ice. There is a small circular region of
open water at the substellar point on the planet (Fig. 10).
However, as we have not included sea ice transport in our
GCM, and glacial flow of thick sea ice could cause a planet
to become fully glaciated (Abbot et al., 2011), this region of
open water is likely unstable. Furthermore, temperatures on
the nightside of the planet reach below the limit for CO2 to
condense at 1 bar surface pressure, indicating the likelihood
for atmospheric freeze-out at this atmospheric concentra-
tion. The nonsynchronous case with the same CO2 level has
a global mean surface temperature that is *11 degrees
warmer (*217 K), although it is completely covered in ice.
The 3 bar CO2 cases, while *17–18 K warmer, exhibit a
similar behavior, with the nonsynchronous case yielding a
global mean surface temperature (*235 K) that is *12 K
warmer than the synchronous case (*223 K). Surface
temperatures on the nightside of the planet in the 3 bar CO2
case are right at the boundary for CO2 condensation at this
surface pressure and CO2 concentration.
High amounts of CO2 would be a relatively straightfor-
ward means of generating habitable surface temperatures on a
planet receiving low instellation from its star. However, the
efficiency of the carbonate-silicate cycle—which has been
shown to be sensitive to a variety of factors, including the
mantle degassing rate of a planet (Driscoll and Bercovici,
2013)—is unknown for Kepler-62f. If the planet has a low
amount of CO2 in its atmosphere, and lacks an active carbon
cycle to adjust the silicate weathering rate with temperature
(Walker et al., 1981), the fraction of habitable surface area
may decrease significantly compared to our simulated cases
with 3 bar and higher CO2. We therefore explored different
orbital configurations that could improve conditions for
habitability on a planet that does not have an effective means
of increasing its concentration of greenhouse gases.
Since we do not know the location of pericenter for the
orbit of Kepler-62f, we explored the effect on instellation of
changes in the VEP of a planet’s orbit, as this can affect the
hemispherical annually averaged instellation on a planet
(Berger, 1978; Berger et al., 1993). Figure 11 shows the
results of CCSM4 simulations assuming a VEP of 0° and
90°, with the obliquity and eccentricity held fixed at 23° and
0.32, respectively. At VEP = 0°, the point where both
hemispheres receive equal amounts of instellation coincides
with the planet’s closest approach to its star. The difference
in monthly instellation is relatively small in the southern
hemisphere, as it receives equal instellation to that received
by the northern hemisphere at pericenter. At a VEP of 90°,
the southern hemisphere receives a significantly higher
percentage of instellation compared to the northern hemi-
sphere during its summer months when the planet is at or
near pericenter. Because of the planet’s obliquity, this is
when the southern hemisphere is angled toward the star.
The obliquity of Kepler-62f is observationally uncon-
strained, so we also explored how different obliquities might
affect the planet’s climate in a low-CO2 scenario. As shown
in Fig. 12, CCSM4 at an obliquity of 60° reveals more
instellation received in the high-latitude regions of the pla-
net than in the tropics. The global mean surface temperature
is still significantly below freezing at both of the simulated
obliquities (23° and 60°), given the Earth-like CO2 levels
and low stellar flux. However, surface temperatures do get
above freezing in the southern hemisphere during its sum-
mer months in the high-obliquity case, with VEP = 90°, in
both our CCSM4 and LMD Generic GCM simulations. This
means that summer in the southern hemisphere occurs near
the planet’s closest approach to its star, as shown in the
schematic diagram in Fig. 13. This results in higher annual
mean surface temperatures in this hemisphere during its
summer months, compared to the northern hemisphere. The
less extreme cold temperatures in the LMD Generic GCM
−80 −60 −40 −20 0 20 40 60 80
0
0.2
0.4
0.6
0.8
1
Latitude (∞)
Seaicecoverfraction
Obl=90
Obl=23.5
FIG. 8. Sea ice cover fraction as a function of latitude for
Kepler-62f after 160-year LMD Generic GCM simulations,
with 3 bar of CO2 in the atmosphere, the maximum stable
initial eccentricity (e = 0.32), Earth-like (blue) and 90°
(green) obliquities, and an Earth-like rotation rate. A VEP of
0° is assumed.
FIG. 9. Surface temperature as a function of latitude for
Kepler-62f after a 120-year LMD Generic GCM simulation,
assuming e = 0, an obliquity of 23.5°, 5 bar of CO2, and an
Earth-like rotation rate. A VEP of 0° is assumed.
EFFECT OF ORBITAL CONFIGURATION ON KEPLER-62F 11
12. FIG. 10. Surface temperature for a synchronous (left) and Earth-like (24 h) rotation rate for Kepler-62f, after a 65- to 100-
year LMD Generic GCM simulation with 1 bar (top) and 3 bar (bottom) of CO2 in the atmosphere. We assumed e = 0,
VEP = 0°, and an obliquity of 0° for all four simulations.
FIG. 11. Annual mean instellation as a function of latitude for Kepler-62f as a function of the month of the year after
40-year CCSM4 simulations, assuming a 12-month annual cycle and a VEP of 0° (left) and 90° (right). The obliquity and
eccentricity of the planet were set to 23° and 0.32, respectively.
12
13. FIG. 12. Top: Annual mean instellation as a function of latitude for Kepler-62f after 40-year CCSM4 simulations,
assuming the PAL of CO2 on Earth (400 ppmv), an obliquity of 23° (blue) and 60° (green). Middle: Surface temperature as a
function of the month of the year, assuming a 12-month annual cycle, for an obliquity of 60° (left) and 23° (right), after
40-year CCSM4 simulations. Bottom: Surface temperature as a function of month of year for an obliquity of 60° (left) and
23° (right), after 60-year LMD Generic GCM simulations. In both models VEP was set to 90°, similar to Earth (102.7°). The
eccentricity was set to 0.32. The less extreme cold temperatures in the LMD Generic GCM simulations are due to a 10 m
maximum thickness limit of sea ice in LMD Generic GCM, while the CCSM4 sea ice thickness near the poles is *30 m.
EFFECT OF ORBITAL CONFIGURATION ON KEPLER-62F 13
14. simulations are due to a 10 m maximum thickness limit of
sea ice in LMD Generic GCM, while the CCSM4 sea ice
thickness near the poles is *30 m. This causes a greater
temperature difference between the models at the poles
during winter months. The reduced ice thickness in LMD
Generic GCM results in a larger conductive heat flux
through the ice, though this has a lower impact for the
warmer climates (e.g., with 3–5 bar and higher CO2), where
there is less ice. We calculated the temperature difference
between the models by equating the residual surface energy
flux with the conductive heat flux through the ice assuming
10 and 30 m ice thicknesses, and found the difference to
equal that between the coldest temperatures in LMD Gen-
eric GCM and CCSM4 (*60 K). Both models indicate that
an orbital configuration that places the summer solstice near
pericenter may amplify the effects of high obliquity and
eccentricity, and this may cause surface melting to occur
during an annual cycle in a low-CO2 scenario. This effect is
also seen clearly in a comparison between LMD Generic
GCM simulations with 3 bar of atmospheric CO2 and VEP
of 0° and 90° (Fig. 14), where the latter simulation shows
warmer surface temperatures in the southern hemisphere
of the planet. We noticed a decrease in planetary ice cover
of *0.6% per 90-degree increase in VEP in our 3 bar CO2
simulations run at 90° obliquity and e = 0.32.
4. Discussion
We explored the plausible range of orbital, rotational, and
atmospheric states of Kepler-62f and found that some permit
habitability, but some do not. A global mean surface tem-
perature similar to modern-day Earth is possible throughout
the planet’s orbit with 5 bar of CO2 in its atmosphere, for
both lower and upper limits of the range of stable initial
eccentricities (e = 0.00 and e = 0.32), assuming present Earth
obliquity. Our simulations with e = 0 yielded lower global
mean surface temperatures, consistent with average in-
stellation decreasing with decreasing eccentricity. These
results indicate that if Kepler-62f has an active carbon cycle,
where CO2 is allowed to build up in the atmosphere as
silicate weathering decreases at lower surface temperatures
(Walker et al., 1981), the best possible scenario for habit-
able surface conditions is one that combines moderate to
high eccentricity with high atmospheric CO2. The maximum
CO2 greenhouse limit for stars with the effective tempera-
ture of Kepler-62 occurs at a stellar flux3
that is well below
FIG. 13. Schematic diagram of as-
sumed orbital configuration for CCSM4
(and select LMD Generic GCM) simu-
lations of Kepler-62f. The angle of the
vernal equinox with respect to peri-
center was set to 90°, similar to Earth
(102.7°).
−80 −60 −40 −20 0 20 40 60 80
220
230
240
250
260
270
280
290
300
Latitude (∞)
SurfaceTemperature(K)
FIG. 14. Surface temperature as a function of latitude for
Kepler-62f, after 160-year LMD Generic GCM simulations
with 3 bar of atmospheric CO2 and VEP 0° (dashed line) and
90° (solid line). An obliquity of 90° and an eccentricity of
0.32 are assumed.
3
*30% of the modern solar constant (Kopparapu et al., 2013a,
2013b).
14 SHIELDS ET AL.
15. that received by Kepler-62f (41% of the modern solar
constant, Borucki et al., 2013). Given that 3–5 bar of CO2
are significantly below this limit (*7–8 bar, Kopparapu
et al., 2013a, 2013b), these levels of CO2 are plausible for
this planet.
Earlier work exploring the possible climates of Kepler-
62f proposed habitable conditions with 1.6 bar of CO2 or
more in the planet’s atmosphere (Kaltenegger et al., 2013).
However, this work was not done with a 3-D GCM and
therefore lacked a full treatment of clouds and atmosphere-
ocean interactions. Using a 3-D GCM, we find that the only
scenario that permits Kepler-62f to exhibit clement tem-
peratures for surface liquid water with 3 bar of CO2 in the
planet’s atmosphere requires stringent orbital configuration
requirements (high eccentricity and obliquity). With an
obliquity of 90°, open water was present over just *20% of
the planet, at polar latitudes. This indicates that it is likely
that more than 1.6 bar of CO2 is required for surface hab-
itability on this planet.
We assumed a five-planet system for Kepler-62 in our n-
body simulations. While there is currently no observational
evidence for additional planets, the existence of other
planets in this system is a clear possibility, and their pres-
ence would certainly affect the eccentricity limit for dy-
namical stability that we have calculated here. Future
discovery of additional planets in this system with transit
timing variations or RV may provide additional dynamical
constraints on the eccentricity of Kepler-62f.
We combined climate simulations using CCSM4 and
LMD Generic GCM to provide a comprehensive exploration
of the possible climates for Kepler-62f given its n-body
model constraints. Previous work using LMD Generic GCM
at a higher resolution (e.g., 128 · 96) yielded similar results
to those at the resolution we employed here (64 · 48), and as
we confirmed that the global mean surface temperature had
not changed by more than 1 K in the last 20 years of sim-
ulation, we are confident that running our simulations for
longer timescales would not change our results significantly.
We verified that simulations assuming Earth-like CO2 levels
in both GCMs exhibited similar (ice-covered) conditions,
confirming the robustness of these simulations to various
assumptions.
Our simulations with higher levels of CO2 resulted in
increasingly higher surface temperatures on the planet. As
CO2 was increased, the changes in global mean surface
temperatures became progressively smaller. This logarith-
mic relationship between CO2 concentration and radiative
forcing is long established (Wigley, 1987). As regions of the
spectrum become opaque, additional CO2 molecules be-
come far less effective at increasing temperatures (Shine
et al., 1990). Thus, the greenhouse effect starts to become
less efficient as a warming mechanism. Additionally, CO2 is
2.5· more effective as a Rayleigh scatterer than Earth’s air
(Kasting, 1991; Forget and Pierrehumbert, 1997), and this
behavior likely contributes to the loss of warming at higher
CO2 concentrations (Kasting, 1991; Kasting et al., 1993;
Selsis et al., 2007).
We have not included the effect of CO2 condensation in
our simulations. As discussed in Section 2.4, at levels of 1–2
bar, CO2 condensation is likely to occur in the upper atmo-
sphere (Pierrehumbert, 2005). Depending on the particle size
of CO2 ice grains, this could result in cooling of the planet
due to the albedo effect of CO2 ice clouds (Kasting, 1991) or
warming by scattering outgoing thermal radiation back to-
ward the surface of the planet (Forget and Pierrehumbert,
1997).
Kopparapu et al. (2013a, 2013b) found that the maximum
CO2 greenhouse limit is *7–8 bar for a star with a similar
effective temperature to that of Kepler-62 (Kopparapu et al.,
2013a, 2013b). We did find that the planetary albedo, which
had decreased with increasing CO2 concentration, started to
increase, albeit slowly, at a CO2 level of 8 bar. However, our
simulations with 8–12 bar of CO2 resulted in global mean
surface temperatures that were still higher than those with
lower CO2, so we conclude that we had not yet reached the
maximum CO2 limit in our simulations and that it may be
higher than originally proposed. Kopparapu et al. (2013a,
2013b) used a 1-D radiative-convective model in their work
and did not include the effect of water clouds or CO2 clouds
in their calculations. While water clouds could increase the
planetary albedo, thereby cooling the planet further, they
may also contribute to the greenhouse effect, as both H2O
and CO2 have strong absorption coefficients in the near-IR,
which increase the amount of radiation absorbed by planets
with lower-mass host stars that emit strongly in the near-IR
(Kasting et al., 1993; Selsis et al., 2007; Joshi and Haberle,
2012; Kopparapu et al., 2013a, 2013b; Shields et al., 2013,
2014). Our results with a 3-D GCM do include water clouds,
though not CO2 clouds. A comprehensive study of the effect
of CO2 condensation as a function of particle size would be
an important step toward identifying its ultimate effect on
planetary climate. Regardless, dense CO2 atmospheres can
be expected to cause more even distributions of heat across
a planet, and reduce the contrast between maximum and
minimum surface temperatures. This is particularly impor-
tant on synchronously rotating planets (Joshi et al., 1997;
Edson et al., 2011), where the difference in instellation on
the dayside and nightside of the planet is large. We also see
this result in our simulations, which show smaller maxi-
mum/minimum surface temperature contrasts with larger
amounts of CO2.
All our simulations assumed an aqua planet configura-
tion, with no land. Previous work exploring the habitability
of planets composed almost entirely of land and orbiting G
dwarf stars suggests that due to their lower thermal inertia
and drier atmospheres, land planets are less susceptible to
snowball episodes than aqua planets, requiring 13% less
instellation to freeze over entirely (Abe et al., 2011). The
presence of land could certainly affect the silicate weath-
ering rate and atmospheric concentration of CO2 on a pla-
net. However, Abbot et al. (2012) found that climate
weathering feedback does not have a strong dependence on
land fraction, as long as the land fraction is at least 0.01.
Edson et al. (2012) found that the amount of CO2 that ac-
cumulates in the atmosphere of a synchronously rotating
planet could be much greater if the substellar point is lo-
cated over an ocean-covered area of the planet, where
continental weathering is minimal, although atmospheric
CO2 concentration could still be limited by seafloor
weathering processes (Edson et al., 2012). Including land in
future simulations of a synchronously rotating Kepler-62f,
using a GCM with a carbonate-silicate cycle included (ra-
ther than assigning a prescribed atmospheric CO2 concen-
tration as we have done here) would be a valuable step
EFFECT OF ORBITAL CONFIGURATION ON KEPLER-62F 15
16. toward assessing the role of surface type in regulating the
atmospheric CO2 inventory on synchronously rotating
planets.
We have concentrated on CO2 as the primary greenhouse
gas in our study of the influence of atmospheric composition
on the habitability of Kepler-62f. Previous work has high-
lighted the role of molecular hydrogen as an incondensable
greenhouse gas that, due to collision-induced absorption,
could allow planets to maintain clement temperatures for
surface liquid water far beyond the traditional outer edge of
a star’s habitable zone (Pierrehumbert and Gaidos, 2011).
Given that the orbital distance of Kepler-62f is interior to
the limit for which an entire primordial H2 envelope could
be lost due to extreme UV-driven atmospheric escape (as-
suming a 3–4 M4 planet), even at apocenter (at an eccen-
tricity of 0.32), an H2 greenhouse may not be an effective
mechanism for warming this planet. Exploring this mecha-
nism in detail in the context of the Kepler-62 system would
be an interesting topic for future study.
4.1. Additional orbital influences
on the climate of Kepler-62f
High amounts of CO2 in the atmosphere of Kepler-62f
would provide for consistently habitable surface conditions
throughout the planet’s orbit at its level of instellation,
thereby offering the best chances for sustained surface liquid
water and life. However, given the uncertainty of an active
carbonate-silicate cycle operating on this planet, we explored
orbital parameters that may periodically improve surface
conditions during the course of an orbit in the event of low-
CO2 atmospheric conditions similar to Earth, though these
conditions would be short-lived. Planetary habitability
throughout the course of an eccentric orbit has been shown to
be most strongly affected by the time-averaged global
instellation—provided there is an ocean to contribute to the
planet’s heat capacity—which is greater at higher eccentric-
ities (Williams and Pollard, 2002). Therefore, although high-
eccentricity planets may spend significant fractions of an
orbit outside of their stars’ habitable zones, high eccentricity
may help these planets maintain habitable surface conditions
over an annual cycle (Kopparapu et al., 2013a, 2013b),
though habitability could be affected by tidal forces and re-
sultant heating at close distances from the star during a
planet’s eccentric orbit (Driscoll and Barnes, 2015). Planets
on eccentric orbits could undergo freeze/thaw cycles de-
pending on the orbital distance of apocenter and pericenter,
respectively, and this could also have important implications
for planetary habitability. Limbach and Turner (2015) found
that catalogued RV systems of higher multiplicity exhibit
lower eccentricities. However, as these are statistical results,
they do not mean that all such systems have low eccentrici-
ties. Furthermore, they used data from RV systems of more
massive planets than those in the Kepler-62 system. There are
currently no observational constraints on the eccentricities of
low-mass, long-period extrasolar planetary systems. Our
calculated eccentricity of 0.32 is entirely plausible for
Kepler-62f and consistent with observations.
Given that the obliquity, rotation rate, and the VEP for
Kepler-62f are unknown, we explored how these factors
might also influence surface habitability on this planet. Our
results indicate that high obliquity, which has been shown to
increase seasonality and stability against snowball episodes
(Williams and Kasting, 1997; Williams and Pollard, 2003;
Spiegel et al., 2009), results in even higher seasonality at
high eccentricity, due to the larger difference between the
orbital distance at pericenter and apocenter (Williams and
Pollard, 2002). This effect is more pronounced in the
southern hemisphere during its summer months, when the
angle of the vernal equinox relative to pericenter is 90°, so
that the planet’s high obliquity significantly increases the
instellation received by this hemisphere. If we had simulated
VEP = 270°, we would expect the northern hemisphere to
exhibit a similar effect, as this is a symmetric problem.
Though we did not include ocean heat transport in our high-
obliquity CCSM4 simulations that yielded global ice cover,
previous work has found that snowball collapse is possible
at high obliquity regardless of the presence of a dynamical
ocean with ocean heat transport (Ferreira et al., 2014).
We identified several orbital configurations that, though
rare, may cause temporarily habitable surface conditions
during the course of an orbit given Earth-like levels of CO2.
Even on an ice-covered high-obliquity planet, our simula-
tions using both models showed that surface temperatures
reached above the freezing point of water during southern
hemisphere summer months, which could cause surface
melting. Our LMD Generic GCM simulations with 3 bar of
CO2 also resulted in higher surface temperatures in the
summer hemisphere with a higher VEP of 90° compared to
0°. The VEP can therefore amplify the warming effects of
high obliquity and eccentricity, and may keep ice from
forming at the poles, or reducing an ice sheet formed during
the planet’s orbit. If the planet experiences large oscillations
in obliquity, polar ice could be prevented from forming on
both hemispheres over an annual cycle, allowing habitable
surface conditions to be maintained on planets with large
eccentricities (Armstrong et al., 2014).
The weaker Coriolis force on synchronously rotating
planets permits rapid heat transport by advection compared
to radiative heat transfer for surface pressures significantly
greater than *0.2 bar (Showman et al., 2013). Combined
with sufficient greenhouse gas concentration levels (Joshi
et al., 1997), this can prevent atmospheric freeze-out on the
nightside of the planet, through the transport of high
amounts of heat from the dayside to the nightside (Pierre-
humbert, 2011). Our results have shown that a synchro-
nously rotating Kepler-62f exhibits a lower global mean
surface temperature than one that is nonsynchronous. This
may underscore a lack of sufficient heat distribution be-
tween the dayside and nightside of the planet at the levels of
CO2 that we have simulated at this planet’s instellation.
Horizontal heat transport is less effective for smaller
amounts of CO2 (Wordsworth et al., 2011), which we
confirmed in the 1 bar CO2 case, where the ratio between the
outgoing thermal fluxes on the nightside and dayside
(a proxy for the redistribution efficiency) is lower. This
caused larger differences between maximum and minimum
surface temperatures on the dayside and nightside of the 1
bar CO2 planet compared to the 3 bar CO2 case.
Additionally, though we did not measure significant dif-
ferences in planetary albedo between the synchronous and
nonsynchronous climate simulations at a given CO2 con-
centration, Kepler-62f lies near the outer edge of its star’s
habitable zone, receiving 41% instellation. On more
16 SHIELDS ET AL.
17. temperate synchronously rotating planets than we have
simulated here, the increased cloud cover that will likely
result on the dayside of a synchronously rotating planet with
an ocean could increase the overall planetary albedo and
reduce surface temperatures (Yang et al., 2013, 2014). The
strength of this effect on distant worlds would depend on the
greenhouse gas concentration and the behavior of the hy-
drological cycle. The results presented here imply that syn-
chronously rotating planets may require more CO2 in their
atmospheres than their nonsynchronous counterparts to
generate equivalent global mean surface temperatures far-
ther out in their star’s habitable zones, and this could affect
planetary habitability.
The n-body model used in this work does not include the
effect of tides. With an orbital period of 267 days, tides are
likely to be weak on Kepler-62f, but they could affect its
rotation period (see Section 3.2), and would certainly be an
important consideration for potentially habitable planets or-
biting even closer to their stars. Tidal effects can lead to
changes in orbital parameters, and may induce capture into
resonances in spin-orbit period, depending on the planet’s
eccentricity and its equatorial ellipticity (the equilibrium
shape attained as a result of the gravitational interaction
between the planet and the host star, Rodrı´guez et al.,
2012). Our work here explored the extreme case of spin-orbit
resonance—synchronous rotation. Nonsynchronous reso-
nance configurations, such as the 3:2 spin-orbit resonance
observed on the planet Mercury (Goldreich and Peale, 1966;
Correia and Laskar, 2004) are also possible and may be
sustained on a planet in a noncircular orbit over long time-
scales (Rodrı´guez et al., 2012). Such configurations become
more likely at larger orbital eccentricities (Malhotra, 1998;
Correia and Laskar, 2004) and are worth exploring.
The habitability requirements we have determined here
did not account for any uncertainties in measured parame-
ters such as stellar luminosity and semimajor axis. Including
such uncertainties might permit a larger habitable surface
area for an even wider range of parameters.
Using constraints from n-body models as input to GCM
simulations permits the exploration of the impact on climate
of the gravitational interactions inherent to a growing pop-
ulation of exoplanets—potentially habitable planets orbiting
in multiple-planet systems around low-mass stars—and the
resulting prospects for the habitability of these worlds. The
techniques presented here can be applied to planets orbiting
stars of any spectral type, with a range of possible atmo-
spheric and surface compositions and dynamical architec-
tures. They can be used to help assess the potential
habitability of newly discovered planets for which obser-
vational measurements are still limited, and can be easily
modified to incorporate new observational data that are
acquired for these planets in the future. While future mis-
sions such as the Transiting Exoplanet Survey Satellite
(TESS, Ricker et al., 2009, 2014) and the James Webb
Space Telescope (Gardner et al., 2006) will not be capable
of characterizing distant planets like Kepler-62f, the pro-
cedure we have carried out here serves as excellent prepa-
ration for closer planets that could be observed and
characterized with these missions. These methods will help
identify which among the habitable-zone planets discovered
to date could exhibit conditions conducive to the presence of
surface liquid water for the widest range of atmospheric and
orbital conditions, making them priorities for these and
other future characterization missions.
5. Conclusions
We carried out a comprehensive exploration of the orbital
evolution of Kepler-62f using an n-body model and found
that the range of eccentricities that Kepler-62f could have
while maintaining dynamical stability within the system was
0.00 £ e £ 0.32. The upper limit of 0.32 is consistent with the
analytic Hill Stability criterion (cf. Gladman, 1993; Barnes
and Greenberg, 2006). A higher upper eccentricity limit is
0.36 assuming a smaller mass (equal to that of the Earth) for
Kepler-62f and a larger mass for Kepler-62e. The con-
straints from the n-body model were used as input to 3-D
climate simulations to explore the possible climates and
habitability of Kepler-62f.
At 41% of the modern solar constant, this planet will likely
require an active carbonate-silicate cycle (or some other
means by which to produce high greenhouse gas concentra-
tions) to maintain clement conditions for surface liquid water.
With 3 bar of CO2 in its atmosphere and an Earth-like rotation
rate, 3-D climate simulations of Kepler-62f yielded open
water across *20% of the planetary surface at the upper limit
of the stable eccentricity range possible for the planet, pro-
vided that it has an extreme obliquity (90°). With 5 bar of CO2
in its atmosphere, a global mean surface temperature similar
to modern-day Earth is possible for the full range of stable
eccentricities and at the present obliquity of Earth. This
higher CO2 level is therefore optimal, as it is below the
maximum CO2 greenhouse limit, and generates habitable
surface conditions for a wide range of orbital configurations
throughout the entire orbital period of the planet. If Kepler-
62f is synchronously rotating, CO2 concentrations above 3
bar would be required to distribute sufficient heat to the
nightside of the planet to avoid atmospheric freeze-out.
We have also shown that surface temperatures above the
freezing point of water during an annual cycle are possible on
the planet if it has a low (Earth-like) level of CO2, provided
that the obliquity is high (60° or greater) compared to an
Earth-like obliquity (23°), and the summer solstice at a given
hemisphere occurs at or near the planet’s closest approach to
its star. This is a rare but possible orbital configuration that
could cause surface melting of an ice sheet formed during a
planet’s orbit and amplify the effects of moderate to high
eccentricity and obliquity. While less optimal than the high-
CO2 case, this may result in periodically habitable surface
conditions in a low-CO2 scenario for Kepler-62f.
Acknowledgments
This material is based upon work supported by the National
Science Foundation under Award No. 1401554, and Grant
Nos. DGE-0718124 and DGE-1256082, and by a University
of California President’s Postdoctoral Fellowship. This work
was facilitated through the use of advanced computational,
storage, and networking infrastructure provided by the Hyak
supercomputer system at the University of Washington. We
would also like to acknowledge high-performance computing
support from Yellowstone (ark:/85065/d7wd3xhc) provided
by NCAR’s Computational and Information Systems Lab-
oratory, sponsored by the National Science Foundation. This
work was performed as part of the NASA Astrobiology
EFFECT OF ORBITAL CONFIGURATION ON KEPLER-62F 17
18. Institute’s Virtual Planetary Laboratory Lead Team, sup-
ported by the National Aeronautics and Space Administration
through the NASA Astrobiology Institute under solicitation
NNH12ZDA002C and Cooperative Agreement Number
NNA13AA93A. The authors wish to thank Dorian Abbot and
an anonymous referee for their comments and suggestions,
which improved the paper. B.C. acknowledges support from
an appointment to the NASA Postdoctoral Program at NAI
Virtual Planetary Laboratory, administered by Oak Ridge
Affiliated Universities. R.B. acknowledges support from NSF
grant AST-1108882. A.S. thanks Brad Hansen, Jonathan
Mitchell, John Johnson, Russell Deitrick, and Tom Quinn for
helpful discussions regarding this work.
Author Disclosure Statement
No competing financial interests exist.
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