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The impact of intrinsic magnetic field on the absorption signatures of
elements probing the upper atmosphere of HD209458b: The signs of an expanding atmosphere of HD209458b have been observed with
far-ultraviolet transmission spectroscopy and in the measurements of transit
absorption by metastable HeI. These observations are interpreted using the
hydrodynamic and Monte-Carlo numerical simulations of various degree of
complexity and consistency. At the same time, no attempt has been made to model
atmospheric escape of a magnetized HD209458b, to see how the planetary magnetic
field might affect the measured transit absorption lines. This paper presents
the global 3D MHD self-consistent simulations of the expanding upper atmosphere
of HD209458b interacting with the stellar wind, and models the observed HI
(Lya), OI (1306 A), CII (1337 A), and HeI (10830 A) transit absorption
features. We find that the planetary dipole magnetic field with the equatorial
surface value of Bp = 1 G profoundly changes the character of atmospheric
material outflow and the related absorption. We also investigate the formation
of planetary magnetosphere in the stellar wind and show that its size is more
determined by the escaping atmosphere flow rather than by the strength of
magnetic field. Fitting of the simulation results to observations enables
constraining the stellar XUV flux and He abundance at ~10 erg cm2/s (at 1 a.u.)
and He/H=0.02, respectively, as well as setting an upper limit for the dipole
magnetic field of Bp<0.1 G on the planetary surface at the equator. This
implies that the magnetic dipole moment of HD209458b should be less than 0.06
of the Jovian value. | astro-ph_EP |
The determination of the trajectory of Chelyabinsk bolide according to
the records of the drive cams and the simulation of the fragments motion in
the atmosphere: The determination of the trajectory of Chelyabinsk bolide according to the
video records is performed and the results of the simulation of the fragment
motion in the atmosphere are showed including its state at that moment. The
methods of distortion compensation and adjusting of the video images with the
calibration images and the iterative method of the trajectory improvement by
azimuths and altitudes are developed. These methods allow improving the
precision of the trajectory tracing to the hundreds of meters in space and to
the tens of arc minutes in the angular measure. | astro-ph_EP |
Extrasolar planet population synthesis I: Method, formation tracks and
mass-distance distribution: With the high number of extrasolar planets discovered by now, it becomes
possible to constrain theoretical formation models in a statistical sense. This
paper is the first in a series in which we carry out a large number of planet
population synthesis calculations. We begin the series with a paper mainly
dedicated to the presentation of our approach, but also the discussion of a
representative synthetic planetary population of solar like stars. Based as
tightly as possible on observational data, we have derived probability
distributions for the most important initial conditions for the planetary
formation process. We then draw sets of initial conditions from these
distributions and obtain the corresponding synthetic planets with our formation
model. Although the main purpose of this paper is the description of our
methods, we present some key results: We find that the variation of the initial
conditions in the limits occurring in nature leads to the formation of planets
of large diversity. This formation process is best visualized in planetary
formation tracks, where different phases of concurrent growth and migration can
be identified. These phases lead to the emergence of sub-populations of planets
distinguishable in a mass-semimajor axis diagram. The most important ones are
the "failed cores", a vast group of core-dominated low mass planets, the
"horizontal branch", a sub-population of Neptune mass planets extending out to
6 AU, and the "main clump", a concentration of giant gaseous giants planets at
around 0.3-2 AU. | astro-ph_EP |
Spectral and orbital characterisation of the directly imaged giant
planet HIP 65426 b: HIP 65426 b is a recently discovered exoplanet imaged during the course of
the SPHERE-SHINE survey. Here we present new $L'$ and $M'$ observations of the
planet from the NACO instrument at the VLT from the NACO-ISPY survey, as well
as a new $Y-H$ spectrum and $K$-band photometry from SPHERE-SHINE. Using these
data, we confirm the nature of the companion as a warm, dusty planet with a
mid-L spectral type. From comparison of its SED with the BT-Settl atmospheric
models, we derive a best-fit effective temperature of $T_{\text{eff}}=1618\pm7$
K, surface gravity $\log g=3.78^{+0.04}_{-0.03}$ and radius $R=1.17\pm0.04$
$R_{\text{J}}$ (statistical uncertainties only). Using the DUSTY and COND
isochrones we estimate a mass of $8\pm1$ $M_{\text{J}}$. Combining the
astrometric measurements from our new datasets and from the literature, we show
the first indications of orbital motion of the companion (2.6$\sigma$
significance) and derive preliminary orbital constraints. We find a highly
inclined orbit ($i=107^{+13}_{-10}$ deg) with an orbital period of
$800^{+1200}_{-400}$ yr. We also report SPHERE sparse aperture masking
observations that investigate the possibility that HIP 65426 b was scattered
onto its current orbit by an additional companion at a smaller orbital
separation. From this data we rule out the presence of brown dwarf companions
with masses greater than 16 $M_{\text{J}}$ at separations larger than 3 AU,
significantly narrowing the parameter space for such a companion. | astro-ph_EP |
Detection of H2O and evidence for TiO/VO in an ultra hot exoplanet
atmosphere: We present a primary transit observation for the ultra hot (Teq~2400K) gas
giant expolanet WASP-121b, made using the Hubble Space Telescope Wide Field
Camera 3 in spectroscopic mode across the 1.12-1.64 micron wavelength range.
The 1.4 micron water absorption band is detected at high confidence (5.4 sigma)
in the planetary atmosphere. We also reanalyze ground-based photometric
lightcurves taken in the B, r', and z' filters. Significantly deeper transits
are measured in these optical bandpasses relative to the near-infrared
wavelengths. We conclude that scattering by high-altitude haze alone is
unlikely to account for this difference, and instead interpret it as evidence
for titanium oxide and vanadium oxide absorption. Enhanced opacity is also
inferred across the 1.12-1.3 micron wavelength range, possibly due to iron
hydride absorption. If confirmed, WASP-121b will be the first exoplanet with
titanium oxide, vanadium oxide, and iron hydride detected in transmission. The
latter are important species in M/L dwarfs, and their presence is likely to
have a significant effect on the overall physics and chemistry of the
atmosphere, including the production of a strong thermal inversion. | astro-ph_EP |
The habitable zone for Earthlike exomoons orbiting Kepler-1625b: The recent announcement of a Neptune-sized exomoon candidate orbiting the
Jupiter-sized object Kepler-1625b has forced us to rethink our assumptions
regarding both exomoons and their host exoplanets. In this paper I describe
calculations of the habitable zone for Earthlike exomoons in orbit of
Kepler-1625b under a variety of assumptions. I find that the candidate exomoon,
Kepler-1625b-i, does not currently reside within the exomoon habitable zone,
but may have done so when Kepler-1625 occupied the main sequence. If it were to
possess its own moon (a "moon-moon") that was Earthlike, this could potentially
have been a habitable world. If other exomoons orbit Kepler-1625b, then there
are a range of possible semimajor axes/eccentricities that would permit a
habitable surface during the main sequence phase, while remaining dynamically
stable under the perturbations of Kepler-1625b-i. This is however contingent on
effective atmospheric CO$_2$ regulation. | astro-ph_EP |
The Influence of Age on the Relative Frequency of Super-Earths and
Sub-Neptunes: There is growing evidence that the population of close-in planets discovered
by the Kepler mission was sculpted by atmospheric loss, though the typical
timescale for this evolution is not well-constrained. Among a highly complete
sample of planet hosts of varying ages the age-dependence of the relative
fraction of super-Earth and sub-Neptune detections can be used to constrain the
rate at which some small planets lose their atmospheres. Using the
California-Kepler Survey (CKS) sample, we find evidence that the ratio of
super-Earth to sub-Neptune detections rises monotonically from 1-10 Gyr. Our
results are in good agreement with an independent study focused on stars hotter
than the Sun, as well as with forward modeling simulations incorporating the
effects of photoevaporation and a CKS-like selection function. We find the
observed trend persists even after accounting for the effects of completeness
or correlations between age and other fundamental parameters. | astro-ph_EP |
An Unprecedented Constraint on Water Content in the Sunlit Lunar
Exosphere Seen by Lunar-Based Ultraviolet Telescope of Chang'e-3 Mission: The content of $\mathrm{OH/H_2O}$ molecules in the tenuous exosphere of the
Moon is still an open issue at present. We here report an unprecedented upper
limit of the content of the OH radicals, which is obtained from the in-situ
measurements carried out \rm by the Lunar-based Ultraviolet Telescope, a
payload of Chinese Chang'e-3 mission. By analyzing the diffuse background in
the images taken by the telescope, the column density and surface concentration
of the OH radicals are inferred to be $<10^{11}\ \mathrm{cm^{-2}}$ and
$<10^{4}\ \mathrm{cm^{-3}}$ (by assuming a hydrostatic equilibrium with a scale
height of 100km), respectively, by assuming that the recorded background is
fully contributed by their resonance fluorescence emission. The resulted
concentration is lower than the previously reported value by about two orders
of magnitude, and is close to the prediction of the sputtering model. In
addition, the same measurements and method allow us to derive a surface
concentration of $<10^{2}\ \mathrm{cm^{-3}}$ for the neutral magnesium, which
is lower than the previously reported upper limit by about two orders of
magnitude. These results are the best known of the OH (MgI) content in the
lunar exosphere to date. | astro-ph_EP |
Global Chemistry and Thermal Structure Models for the Hot Jupiter
WASP-43b and Predictions for JWST: The James Webb Space Telescope (JWST) is expected to revolutionize the field
of exoplanets. The broad wavelength coverage and the high sensitivity of its
instruments will allow characterization of exoplanetary atmospheres with
unprecedented precision. Following the Call for the Cycle 1 Early Release
Science Program, the Transiting Exoplanet Community was awarded time to observe
several targets, including WASP-43b. The atmosphere of this hot Jupiter has
been intensively observed but still harbors some mysteries, especially
concerning the day-night temperature gradient, the efficiency of the
atmospheric circulation, and the presence of nightside clouds. We will
constrain these properties by observing a full orbit of the planet and
extracting its spectroscopic phase curve in the 5--12 $\mu$m range with
JWST/MIRI. To prepare for these observations, we performed an extensive
modeling work with various codes: radiative transfer, chemical kinetics, cloud
microphysics, global circulation models, JWST simulators, and spectral
retrieval. Our JWST simulations show that we should achieve a precision of 210
ppm per 0.1 $\mu$m spectral bin on average, which will allow us to measure the
variations of the spectrum in longitude and measure the night-side emission
spectrum for the first time. If the atmosphere of WASP-43b is clear, our
observations will permit us to determine if its atmosphere has an equilibrium
or disequilibrium chemical composition, providing eventually the first
conclusive evidence of chemical quenching in a hot Jupiter atmosphere. If the
atmosphere is cloudy, a careful retrieval analysis will allow us to identify
the cloud composition. | astro-ph_EP |
Pre-LHB Evolution of the Earth's Obliquity: The Earth's obliquity is stabilized by the Moon, which facilitates a rapid
precession of the Earth's spin-axis, de-tuning the system away from resonance
with orbital modulation. It is however, likely that the architecture of the
Solar System underwent a dynamical instability-driven transformation, where the
primordial configuration was more compact. Hence, the characteristic
frequencies associated with orbital perturbations were likely faster in the
past, potentially allowing for secular resonant encounters. In this work we
examine if at any point in the Earth's evolutionary history, the obliquity
varied significantly. Our calculations suggest that even though the orbital
perturbations were different, the system nevertheless avoided resonant
encounters throughout its evolution. This indicates that the Earth obtained its
current obliquity during the formation of the Moon. | astro-ph_EP |
TRAPPIST-1h as an Exo-Titan. I. The Role of Assumptions about
Atmospheric Parameters in Understanding an Exoplanet Atmosphere: The TRAPPIST-1 system is home to at least seven terrestrial planets and is a
target of interest for future James Webb Space Telescope (JWST) observations.
Additionally, these planets will be of interest to future missions making
observations in the ultraviolet (UV). Although several of these planets are
located in the traditional habitable zone, where liquid water could exist on
the surface, TRAPPIST-1h is interesting to explore as a potentially habitable
ocean world analog. In this study, we evaluate the observability of a
Titan-like atmosphere on TRAPPIST-1h. The ability of the JWST or a future UV
mission to detect specific species in the atmosphere at TRAPPIST-1h will depend
on how far each species extends from the surface. In order to understand the
conditions required for detection, we evaluate the input parameters used in
one-dimensional models to simulate the structure of Titan-like atmospheres.
These parameters include surface temperature and pressure, temperature profile
as a function of distance from the surface, composition of the minor species
relative to N 2, and the eddy diffusion coefficient. We find that JWST
simulated spectra for cloud- and haze-free atmospheres are most sensitive to
surface temperature, temperature gradients with altitude, and surface pressure.
The importance of temperature gradients in JWST observations shows that a
simple isothermal scale height is not ideal for determining temperature or
atmospheric mean molecular mass in transit spectra from exoplanet atmospheres.
We demonstrate that UV transmission spectra are sensitive to the upper
atmosphere, where the exobase can be used to approximate the vertical extent of
the atmosphere. | astro-ph_EP |
Yearly and seasonal variations of low albedo surfaces on Mars in the
OMEGA/MEx dataset: Constraints on aerosols properties and dust deposits: The time variations of spectral properties of dark martian surface features
are investigated using the OMEGA near-IR dataset. The analyzed period covers
two Mars years, spanning from early 2004 to early 2008 (includes the 2007
global dust event). Radiative transfer modeling indicates that the apparent
albedo variations of low to mid-latitude dark regions are consistent with those
produced by the varying optical depth of atmospheric dust as measured
simultaneously from the ground by the Mars Exploration Rovers. We observe only
a few significant albedo changes that can be attributed to surface phenomena.
They are small-scaled and located at the boundaries between bright and dark
regions. We then investigate the variations of the mean particle size of
aerosols using the evolution of the observed dark region spectra between 1 and
2.5 {\mu}m. Overall, we find that the observed changes in the spectral slope
are consistent with a mean particle size of aerosols varying with time between
1 and 2 {\mu}m. Observations with different solar zenith angles make it
possible to characterize the aerosol layer at different altitudes, revealing a
decrease of the particle size of aerosols as altitude increases. | astro-ph_EP |
Deep exploration of $ε$ Eridani with Keck Ms-band vortex
coronagraphy and radial velocities: mass and orbital parameters of the giant
exoplanet: We present the most sensitive direct imaging and radial velocity (RV)
exploration of $\epsilon$ Eridani to date. $\epsilon$ Eridani is an adolescent
planetary system, reminiscent of the early Solar system. It is surrounded by a
prominent and complex debris disk which is likely stirred by one or several gas
giant exoplanets. The discovery of the RV signature of a giant exoplanet was
announced 15 years ago, but has met with scrutiny due to possible confusion
with stellar noise. We confirm the planet with a new compilation and analysis
of precise RV data spanning 30 years, and combine it with upper limits from our
direct imaging search, the most sensitive ever performed. The deep images were
taken in the Ms band (4.7$\mu$m) with the vortex coronagraph recently installed
in W.M. Keck Observatory's infrared camera NIRC2, which opens a sensitive
window for planet searches around nearby adolescent systems. The RV data and
direct imaging upper limit maps were combined in an innovative joint Bayesian
analysis, providing new constraints on the mass and orbital parameters of the
elusive planet. $\epsilon$ Eridani b has a mass of $0.78^{+0.38}_{-0.12}$
$M_{Jup}$ and is orbiting $\epsilon$ Eridani at about $3.48\pm 0.02$ AU with a
period of $7.37 \pm 0.07$ years. The eccentricity of $\epsilon$ Eridani b's
orbit is $0.07^{+0.06}_{-0.05}$, an order of magnitude smaller than early
estimates and consistent with a circular orbit. We discuss our findings from
the standpoint of planet-disk interactions and prospects for future detection
and characterization with the James Webb Space Telescope. | astro-ph_EP |
NEMESIS: Exoplanet Transit Survey of Nearby M-Dwarfs in TESS FFIs I: In this work, we present the analysis of 33,054 M-dwarf stars located within
100 parsecs in the Transiting Exoplanet Survey Satellite (TESS) Full Frame
Images (FFIs) of the observed sectors 1 to 5. We present a new pipeline called
NEMESIS which was developed to extract detrended photometry and perform transit
searches of single sector data in TESS FFIs. As many M-dwarfs are faint and are
not observed with a 2 minute cadence by TESS, FFI transit surveys can give an
empirical validation of how many planets are missed by using the 30 minute
cadence data. In this work, we detected 183 threshold crossing events and
present 29 planet candidates for sectors 1 to 5, 24 of which are new
detections. Our sample contains orbital periods ranging from 1.25 to 6.84 days
and planetary radii from 1.26 to 5.31 Earth radii. With the addition of our new
planet candidate detections along with previous detections observed in sectors
1 to 5, we calculate an integrated occurrence rate of 2.49 +/- 1.58 planets per
star for the period range between [1,9] days and planet radius range between
[0.5,11] Earth radii. We project an estimated yield of 122 +/- 11 transit
detections of nearby M-dwarfs. 23 of our new candidates have Signal to Noise
ratios > 7, Transmission Spectroscopy Metrics > 38 and Emission Spectroscopy
Metrics > 10. We provide all of our data products for our planet candidates
through the Filtergraph data visualization service located at
https://filtergraph.com/NEMESIS. | astro-ph_EP |
H2-Induced Pressure Broadening and Pressure Shift in the P-Branch of the
v3 Band of CH4 from 300 to 700 K: For accurate modelling of observations of exoplanet atmospheres,
quantification of the pressure broadening of infrared absorption lines for and
by a variety of gases at elevated temperatures is needed. High-resolution
high-temperature H2-pressure-broadened spectra are recorded for the CH4 v3-band
P-branch. Measured linewidths for 116 transitions between 2840 and 3000 cm^{-1}
with temperature and pressures ranging between 300 and 700 K, and 10 and 933
Torr, respectively, were used to find rotation- and
tetrahedral-symmetry-dependent coefficients for pressure and temperature
broadening and pressure-induced lineshifts. The new pressure-broadening data
will be useful in radiative-transfer models for retrieving the properties of
observed expolanet atmospheres. | astro-ph_EP |
High-resolution transmission spectroscopy of ultra-hot Jupiter WASP-33b
with NEID: We report an attempt to detect molecular and atomic species in the atmosphere
of the ultra-hot Jupiter WASP-33b using the high-resolution echelle
spectrograph NEID with a wavelength coverage of 380$-$930 nm. By analyzing the
transmission spectrum of WASP-33b using the line-by-line technique and the
cross-correlation technique, we confirm previous detection of H$\alpha$,
H$\beta$, H$\gamma$, and Ca II infrared triplets. We find no evidence for a
significant day-to-night wind in WASP-33b, taking into account the effects of
stellar pulsations using a relatively novel GP method and poorly constrained
systemic velocity measurements. We also detect the previously reported
pre-transit absorption signal, which may be a pulsation mode induced by the
planet. Combined with previous CARMENES and HARPS-N observations, we report the
non-detection of TiO, Ti I, and V I in the transmission spectrum, while they
were already detected in the dayside atmosphere of WASP-33b. This implies a
difference in the chemical compositions and abundances between the dayside and
terminator atmospheres of WASP-33b, and certainly requires further improvements
in the sensitivity of the detection methods. | astro-ph_EP |
Global Models of Runaway Accretion in White Dwarf Debris Disks: A growing sample of white dwarfs (WDs) with metal-enriched atmospheres are
accompanied by excess infrared emission, indicating that they are encircled by
a compact dusty disk of solid debris. Such `WD debris disks' are thought to
originate from the tidal disruption of asteroids or other minor bodies, but the
precise mechanism(s) responsible for transporting matter to the WD surface
remains unclear, especially in those systems with the highest inferred metal
accretion rates dM_Z/dt ~ 1e8-1e10 g/s. Here we present global time-dependent
calculations of the coupled evolution of the gaseous and solid components of WD
debris disks. Solids transported inwards (initially due to PR drag) sublimate
at tens of WD radii, producing a source of gas that accretes onto the WD
surface and viscously spreads outwards in radius, where it overlaps with the
solid disk. If the aerodynamic coupling between the solids and gaseous disks is
sufficiently strong (and/or the gas viscosity sufficiently weak), then gas
builds up near the sublimation radius faster than it can viscously spread away.
Since the rate of drag-induced solid accretion increases with gas density, this
results in a runaway accretion process, during which the WD accretion rate
reaches values orders of magnitude higher than can be achieved by PR drag
alone. We explore the evolution of WD debris disks across a wide range of
physical conditions and calculate the predicted distribution of observed
accretion rates dM_Z/dt, finding reasonable agreement with the current sample.
Although the conditions necessary for runaway accretion are at best marginally
satisfied given the minimal level of aerodynamic drag between circular gaseous
and solid disks, the presence of other stronger forms of solid-gas
coupling---such as would result if the gaseous disk is only mildly
eccentric---substantially increase the likelihood of runaway accretion. | astro-ph_EP |
EOS: Atmospheric Radiative Transfer in Habitable Worlds with HELIOS: We present EOS, a procedure for determining the Outgoing Longwave Radiation
(OLR) and top-of-atmosphere (TOA) albedo for a wide range of conditions
expected to be present in the atmospheres of rocky planets with temperate
conditions. EOS is based on HELIOS and HELIOS-K, which are novel and publicly
available atmospheric radiative transfer (RT) codes optimized for fast
calculations with GPU processors. These codes were originally developed for the
study of giant planets. In this paper we present an adaptation for applications
to terrestrial-type, habitable planets, adding specific physical recipes for
the gas opacity and vertical structure of the atmosphere. To test the
reliability of the procedure we assessed the impact of changing line opacity
profile, continuum opacity model, atmospheric lapse rate and tropopause
position prescriptions on the OLR and the TOA albedo. The results obtained with
EOS are in line with those of other RT codes running on traditional CPU
processors, while being at least one order of magnitude faster. The adoption of
OLR and TOA albedo data generated with EOS in a zonal and seasonal climate
model correctly reproduce the fluxes of the present-day Earth measured by the
CERES spacecraft. The results of this study disclose the possibility to
incorporate fast RT calculations in climate models aimed at characterizing the
atmospheres of habitable exoplanets. | astro-ph_EP |
A Circumbinary Debris Disk in a Polluted White Dwarf System: Planetary systems commonly survive the evolution of single stars, as
evidenced by terrestrial-like planetesimal debris observed orbiting and
polluting the surfaces of white dwarfs. This letter reports the identification
of a circumbinary dust disk surrounding a white dwarf with a substellar
companion in a 2.27 hr orbit. The system bears the dual hallmarks of
atmospheric metal pollution and infrared excess, however the standard (flat and
opaque) disk configuration is dynamically precluded by the binary. Instead, the
detected reservoir of debris must lie well beyond the Roche limit in an
optically thin configuration, where erosion by stellar irradiation is
relatively rapid. This finding demonstrates that rocky planetesimal formation
is robust around close binaries, even those with low mass ratios. | astro-ph_EP |
Jupiter's Ammonia Distribution Derived from VLA Maps at 3--37 GHz: We observed Jupiter four times over a full rotation (10 hrs) with the
upgraded Karl G. Jansky Very Large Array (VLA) between December 2013 and
December 2014. Preliminary results at 4-17 GHz were presented in de Pater et
al. (2016); in the present paper we present the full data set at frequencies
between 3 and 37 GHz. Major findings are: (i) the radio-hot belt at
8.5--11$^\circ$N latitude, near the interface between the North Equatorial Belt
(NEB) and the Equatorial Zone (EZ) is prominent at all frequencies (3--37 GHz).
Its location coincides with the southern latitudes of the NEB (7--17$^{\circ}$
N). (ii) Longitude-smeared maps reveal belts and zones at all frequencies at
latitudes $\lesssim |20^\circ|$. The lowest brightness temperature is in the EZ
near a latitude of 4$^\circ$N, and the NEB has the highest brightness
temperature near 11$^\circ$N. The bright part of the NEB increases in
latitudinal extent (spreads towards the north) with deceasing frequency, i.e.,
with depth into the atmosphere. In longitude-resolved maps, several belts, in
particular in the southern hemisphere, are not continuous along the latitude
line, but broken into small segments as if caused by an underlying wave. (iii)
Model fits to longitude-smeared spectra are obtained at each latitude. These
show a high NH$_3$ abundance (volume mixing ratio $\sim 4 \times 10^{-4}$) in
the deep ($P>8-10$ bar) atmosphere, decreasing at higher altitudes due to cloud
formation (e.g., in zones), or dynamics in combination with cloud condensation
(belts). In the NEB ammonia gas is depleted down to at least the 20 bar level
with an abundance of $1.75 \times 10^{-4}$. (iv) Using the entire VLA dataset,
we confirm that the planet is extremely dynamic in the upper layers of the
atmosphere, at $P<$2--3 bar, i.e., at the altitudes where clouds form.
[Abridged] | astro-ph_EP |
Titan-Hyperion Resonance and the Tidal Q of Saturn: Lainey et al. (2012), by re-analyzing long-baseline astrometry of Saturn's
moons, have found that the moons' tidal evolution is much faster than
previously thought, implying an order of magnitude stronger tidal dissipation
within Saturn. This result is controversial and implies recent formation of at
least some of the mid-sized icy moons of Saturn. Here we show that this more
intensive tidal dissipation is in full agreement with the evolved state of the
Titan-Hyperion resonance. This resonance was previously thought to be non-tidal
in origin, as the amount of tidal evolution required for its assembly is beyond
what is possible in models that assume that all the major moons are primordial.
We find that the survival of the Titan-Hyperion resonance is in agreement with
a past Titan-Iapetus 5:1 resonance, but not with unbroken tidal evolution of
Rhea from the rings to its current distance. | astro-ph_EP |
An upper limit on late accretion and water delivery in the Trappist-1
exoplanet system: The Trappist-1 system contains seven roughly Earth-sized planets locked in a
multi-resonant orbital configuration, which has enabled precise measurements of
the planets' masses and constrained their compositions. Here we use the
system's fragile orbital structure to place robust upper limits on the planets'
bombardment histories. We use N-body simulations to show how perturbations from
additional objects can break the multi-resonant configuration by either
triggering dynamical instability or simply removing the planets from resonance.
The planets cannot have interacted with more than ${\sim 5\%}$ of an Earth mass
(${M_\oplus}$) in planetesimals -- or a single rogue planet more massive than
Earth's Moon -- without disrupting their resonant orbital structure. This
implies an upper limit of ${10^{-4}}$ to ${10^{-2} M_\oplus}$ of late accretion
on each planet since the dispersal of the system's gaseous disk. This is
comparable to or less than the late accretion on Earth after the Moon-forming
impact, and demonstrates that the Trappist-1 planets' growth was complete in
just a few million years, roughly an order of magnitude faster than Earth's.
Our results imply that any large water reservoirs on the Trappist-1 planets
must have been incorporated during their formation in the gaseous disk. | astro-ph_EP |
Olivine-Carbonate Mineralogy of Jezero Crater: A well-preserved, ancient delta deposit, in combination with ample exposures
of Mg-carbonate rich materials, make Jezero Crater in Nili Fossae a compelling
astrobiological site and a top candidate for future landed missions to Mars. We
use CRISM observations to characterize the surface mineralogy of the crater and
surrounding watershed. We have identified a three- endmember sequence of
olivine-bearing lithologies that we hypothesize are distinguished by their Mg
content. We find that Mg-carbonates are consistently identified in association
with one of the olivine-bearing lithologies, although that lithology is not
fully carbonatized. Surprisingly, this lithology contains relatively Fe-rich
olivine. We address a range of formation scenarios, including the possibility
that these olivine and carbonate associations are indicators of
serpentinization on early Mars. These deposits provide an opportunity for
deepening our understanding of early Mars by revealing the thermal history of
the martian interior and potentially changes in its tectonic regime with time. | astro-ph_EP |
The extrasolar planet Gliese 581 d: a potentially habitable planet?
(Corrigendum to arXiv:1009.5814): We report here that the equation for H2O Rayleigh scattering was incorrectly
stated in the original paper [arXiv:1009.5814]. Instead of a quadratic
dependence on refractivity r, we accidentally quoted an r^4 dependence. Since
the correct form of the equation was implemented into the model, scientific
results are not affected. | astro-ph_EP |
Detection of water absorption in the day side atmosphere of HD 189733 b
using ground-based high-resolution spectroscopy at 3.2 microns: We report a 4.8 sigma detection of water absorption features in the day side
spectrum of the hot Jupiter HD 189733 b. We used high-resolution (R~100,000)
spectra taken at 3.2 microns with CRIRES on the VLT to trace the
radial-velocity shift of the water features in the planet's day side atmosphere
during 5 h of its 2.2 d orbit as it approached secondary eclipse. Despite
considerable telluric contamination in this wavelength regime, we detect the
signal within our uncertainties at the expected combination of systemic
velocity (Vsys=-3 +5-6 km/s) and planet orbital velocity (Kp=154 +14-10 km/s),
and determine a H2O line contrast ratio of (1.3+/-0.2)x10^-3 with respect to
the stellar continuum. We find no evidence of significant absorption or
emission from other carbon-bearing molecules, such as methane, although we do
note a marginal increase in the significance of our detection to 5.1 sigma with
the inclusion of carbon dioxide in our template spectrum. This result
demonstrates that ground-based, high-resolution spectroscopy is suited to
finding not just simple molecules like CO, but also to more complex molecules
like H2O even in highly telluric contaminated regions of the Earth's
transmission spectrum. It is a powerful tool that can be used for conducting an
immediate census of the carbon- and oxygen-bearing molecules in the atmospheres
of giant planets, and will potentially allow the formation and migration
history of these planets to be constrained by the measurement of their
atmospheric C/O ratios. | astro-ph_EP |
An automated procedure for the detection of the Yarkovsky effect and
results from the ESA NEO Coordination Centre: Context: The measurement of the Yarkovsky effect on near-Earth asteroids
(NEAs) is common practice in orbit determination today, and the number of
detections will increase with the developments of new and more accurate
telescopic surveys. However, the process of finding new detections and
identifying spurious ones is not yet automated, and it often relies on personal
judgment. Aims: We aim to introduce a more automated procedure that can search
for NEA candidates to measure the Yarkovsky effect, and that can identify
spurious detections. Methods: The expected semi-major axis drift on an NEA
caused by the Yarkovsky effect was computed with a Monte Carlo method on a
statistical model of the physical parameters of the asteroid that relies on the
most recent NEA population models and data. The expected drift was used to
select candidates in which the Yarkovsky effect might be detected, according to
the current knowledge of their orbit and the length of their observational arc.
Then, a nongravitational acceleration along the transverse direction was
estimated through orbit determination for each candidate. If the detected
acceleration was statistically significant, we performed a statistical test to
determine whether it was compatible with the Yarkovsky effect model. Finally,
we determined the dependence on an isolated tracklet. Results: Among the known
NEAs, our procedure automatically found 348 detections of the Yarkovsky effect
that were accepted. The results are overall compatible with the predicted trend
with the the inverse of the diameter, and the procedure appears to be efficient
in identifying and rejecting spurious detections. This algorithm is now adopted
by the ESA NEO Coordination Centre to periodically update the catalogue of NEAs
with a measurable Yarkovsky effect, and the results are automatically posted on
the web portal. | astro-ph_EP |
Water ice in the Kuiper belt: We examine a large collection of low resolution near-infrared spectra of
Kuiper belt objects and centaurs in an attempt to understand the presence of
water ice in the Kuiper belt. We find that water ice on the surface of these
objects occurs in three separate manners: (1) Haumea family members uniquely
show surfaces of nearly pure water ice, presumably a consequence of the
fragmentation of the icy mantle of a larger differentiated proto-Haumea; (2)
large objects with absolute magnitudes of $H<3$ (and a limited number to H=4.5)
have surface coverings of water ice - perhaps mixed with ammonia - that appears
to be related to possibly ancient cryovolcanism on these large objects; and (3)
smaller KBOs and centaurs which are neither Haumea family members nor
cold-classical KBOs appear to divide into two families (which we refer to as
"neutral" and "red"), each of which is a mixture of a common nearly-neutral
component and either a slightly red or very red component that also includes
water ice. A model suggesting that the difference between neutral and red
objects is due to formation in an early compact solar system either inside or
outside, respectively, of the ~20 AU methanol evaporation line is supported by
the observation that methanol is only detected on the reddest objects, which
are those which would be expected to have the most of the methanol containing
mixture. | astro-ph_EP |
The Sizes and Albedos of Centaurs 2014 YY $_{49}$ and 2013 NL $_{24}$
from Stellar Occultation Measurements by RECON: In 2019, the Research and Education Collaborative Occultation Network (RECON)
obtained multiple-chord occultation measurements of two centaur objects: 2014
YY$_{49}$ on 2019 January 28 and 2013 NL$_{24}$ on 2019 September 4. RECON is a
citizen-science telescope network designed to observe high-uncertainty
occultations by outer solar system objects. Adopting circular models for the
object profiles, we derive a radius $r=16^{+2}_{-1}$km and a geometric albedo
$p_V=0.13^{+0.015}_{-0.024}$ for 2014 YY$_{49}$, and a radius $r=66
^{+5}_{-5}$km and geometric albedo $p_V = 0.045^{+0.006}_{-0.008}$ for 2013
NL$_{24}$. To the precision of these measurements, no atmosphere or rings are
detected for either object. The two objects measured here are among the
smallest distant objects measured with the stellar occultation technique. In
addition to these geometric constraints, the occultation measurements provide
astrometric constraints for these two centaurs at a higher precision than has
been feasible by direct imaging. To supplement the occultation results, we also
present an analysis of color photometry from the Pan-STARRS surveys to
constrain the rotational light curve amplitudes and spectral colors of these
two centaurs. We recommend that future work focus on photometry to more
deliberately constrain the objects' colors and light curve amplitudes, and on
follow-on occultation efforts informed by this astrometry. | astro-ph_EP |
Coupling between corotation and Lindblad resonances in the elliptic
planar three-body problem: We investigate the dynamics of two satellites with masses $\mu_s$ and
$\mu'_s$ orbiting a massive central planet in a common plane, near a first
order mean motion resonance $m$+1:$m$ ($m$ integer). We consider only the
resonant terms of first order in eccentricity in the disturbing potential of
the satellites, plus the secular terms causing the orbital apsidal precessions.
We obtain a two-degree of freedom system, associated with the two critical
resonant angles $\phi= (m+1)\lambda' -m\lambda - \varpi$ and $\phi'=
(m+1)\lambda' -m\lambda - \varpi'$, where $\lambda$ and $\varpi$ are the mean
longitude and longitude of periapsis of $\mu_s$, respectively, and where the
primed quantities apply to $\mu'_s$. We consider the special case where $\mu_s
\rightarrow 0$ (restricted problem). The symmetry between the two angles $\phi$
and $\phi'$ is then broken, leading to two different kinds of resonances,
classically referred to as Corotation Eccentric resonance (CER) and Lindblad
Eccentric Resonance (LER), respectively. We write the four reduced equations of
motion near the CER and LER, that form what we call the CoraLin model. This
model depends upon only two dimensionless parameters that control the dynamics
of the system: the distance $D$ between the CER and LER, and a forcing
parameter $\epsilon_L$ that includes both the mass and the orbital eccentricity
of the disturbing satellite. Three regimes are found: for $D=0$ the system is
integrable, for $D$ of order unity, it exhibits prominent chaotic regions,
while for $D$ large compared to 2, the behavior of the system is regular and
can be qualitatively described using simple adiabatic invariant arguments. We
apply this model to three recently discovered small Saturnian satellites
dynamically linked to Mimas through first order mean motion resonances :
Aegaeon, Methone and Anthe. | astro-ph_EP |
Exoplanet Atmospheres at High Spectral Resolution: The spectrum of an exoplanet reveals the physical, chemical, and biological
processes that have shaped its history and govern its future. However,
observations of exoplanet spectra are complicated by the overwhelming glare of
their host stars. This review chapter focuses on high resolution spectroscopy
(HRS; R=25,000-100,000), which helps to disentangle and isolate the exoplanet's
spectrum. At high spectral resolution, molecular features are resolved into a
dense forest of individual lines in a pattern that is unique for a given
molecule. For close-in planets, the spectral lines undergo large Doppler shifts
during the planet's orbit, while the host star and Earth's spectral features
remain essentially stationary, enabling a velocity separation of the planet.
For slower-moving, wide-orbit planets, HRS aided by high contrast imaging
instead isolates their spectra using their spatial separation. The lines in the
exoplanet spectrum are detected by comparing them with high resolution spectra
from atmospheric modelling codes; essentially a form of fingerprinting for
exoplanet atmospheres. This measures the planet's orbital velocity, and helps
define its true mass and orbital inclination. Consequently, HRS can detect both
transiting and non-transiting planets. It also simultaneously characterizes the
planet's atmosphere due to its sensitivity to the depth, shape, and position of
the planet's spectral lines. These are altered by the planet's atmospheric
composition, structure, clouds, and dynamics, including day-to-night winds and
its rotation period. This chapter describes the HRS technique in detail,
highlighting its successes in exoplanet detection and characterization, and
concludes with the future prospects of using HRS to identify biomarkers on
nearby rocky worlds, and map features in the atmospheres of giant exoplanets. | astro-ph_EP |
The timeline of the Lunar bombardment - revisited: The timeline of the lunar bombardment in the first Gy of the Solar System
remains unclear. Some basin-forming impacts occurred 3.9-3.7Gy ago. Many other
basins formed before, but their exact ages are not precisely known. There are
two possible interpretations of the data: in the cataclysm scenario there was a
surge in the impact rate approximately 3.9Gy ago, while in the accretion tail
scenario the lunar bombardment declined since the era of planet formation and
the latest basins formed in its tail-end. Here, we revisit the work of
Morbidelli et al.(2012) that examined which scenario could be compatible with
both the lunar crater record in the 3-4Gy period and the abundance of highly
siderophile elements (HSE) in the lunar mantle. We use updated numerical
simulations of the fluxes of impactors. Under the traditional assumption that
the HSEs track the total amount of material accreted by the Moon since its
formation, we conclude that only the cataclysm scenario can explain the data.
The cataclysm should have started ~3.95Gy ago. However we show that HSEs could
have been sequestered from the lunar mantle due to iron sulfide exsolution
during magma ocean crystallization, followed by mantle overturn. Based on the
hypothesis that the lunar magma ocean crystallized about 100-150My after Moon
formation, and therefore that HSEs accumulated in the lunar mantle only after
this time, we show that the bombardment in the 3-4Gy period can be explained in
the accretion tail scenario. This hypothesis would also explain why the Moon
appears so depleted in HSEs relative to the Earth. We also extend our analysis
of the cataclysm and accretion tail scenarios to the case of Mars. The
accretion tail scenario requires a global resurfacing event on Mars ~4.4Gy ago,
possibly associated with the formation of the Borealis basin, and it is
consistent with the HSE budget of the planet. | astro-ph_EP |
Scattered light images of spiral arms in marginally gravitationally
unstable discs with an embedded planet: Scattered light images of transition discs in the near-infrared often show
non-axisymmetric structures in the form of wide-open spiral arms in addition to
their characteristic low-opacity inner gap region. We study self-gravitating
discs and investigate the influence of gravitational instability on the shape
and contrast of spiral arms induced by planet-disc interactions.
Two-dimensional non-isothermal hydrodynamical simulations including viscous
heating and a cooling prescription are combined with three-dimensional dust
continuum radiative transfer models for direct comparison to observations. We
find that the resulting contrast between the spirals and the surrounding disc
in scattered light is by far higher for pressure scale height variations, i.e.
thermal perturbations, than for pure surface density variations. Self-gravity
effects suppress any vortex modes and tend to reduce the opening angle of
planet-induced spirals, making them more tightly wound. If the disc is only
marginally gravitationally stable with a Toomre parameter around unity, an
embedded massive planet (planet-to-star mass ratio of $10^{-2}$) can trigger
gravitational instability in the outer disc. The spirals created by this
instability and the density waves launched by the planet can overlap resulting
in large-scale, more open spiral arms in the outer disc. The contrast of these
spirals is well above the detection limit of current telescopes. | astro-ph_EP |
On the origin and composition of Theia: Constraints from new models of
the Giant Impact: Knowing the isotopic composition of Theia, the proto-planet which collided
with the Earth in the Giant Impact that formed the Moon, could provide
interesting insights on the state of homogenization of the inner solar system
at the late stages of terrestrial planet formation. We use the known isotopic
and modeled chemical compositions of the bulk silicate mantles of Earth and
Moon and combine them with different Giant Impact models, to calculate the
possible ranges of isotopic composition of Theia in O, Si, Ti, Cr, Zr and W in
each model. We compare these ranges to the isotopic composition of carbonaceous
chondrites, Mars, and other solar system materials. In the absence of
post-impact isotopic re-equilibration, the recently proposed high angular
momentum models of the Giant Impact ("impact-fission", Cuk & Stewart, 2012; and
"merger", Canup, 2012) allow - by a narrow margin - for a Theia similar to
CI-chondrites, and Mars. The "hit-and-run" model (Reufer et al., 2012) allows
for a Theia similar to enstatite-chondrites and other Earth-like materials. If
the Earth and Moon inherited their different mantle FeO contents from the bulk
mantles of the proto-Earth and Theia, the high angular momentum models cannot
explain the observed difference. However, both the hit-and-run as well as the
classical or "canonical" Giant Impact model naturally explain this difference
as the consequence of a simple mixture of two mantles with different FeO.
Therefore, the simplest way to reconcile the isotopic similarity, and FeO
dissimilarity, of Earth and Moon is a Theia with an Earth-like isotopic
composition and a higher (~20%) mantle FeO content. | astro-ph_EP |
Planet Packing in Circumbinary Systems: The recent discovery of planets orbiting main sequence binaries will provide
crucial constraints for theories of binary and planet formation. The formation
pathway for these planets is complicated by uncertainties in the formation
mechanism of the host stars. In this paper, we compare the dynamical states of
single and binary star planetary systems. Specifically, we pose two questions:
(1) What does it mean for a circumbinary system to be dynamically packed? (2)
How many systems are required to differentiate between a population of packed
or sparse planets? We determine when circumbinary systems become dynamically
unstable as a function of the separation between the host-stars and the inner
planet, and the first and second planets. We show that these represent unique
stability constraints compared to single-star systems. We find that although
the existing Kepler data is insufficient to distinguish between a population of
packed or sparse circumbinary systems, a more thorough study of circumbinary
TTVs combined with an order of magnitude increase in the number of systems may
prove conclusive. Future space missions such as TESS provide the best
opportunity for increasing the sample size. | astro-ph_EP |
The vertical structure of Jupiter's equatorial zonal wind above the
cloud deck, derived using mesoscale gravity waves: Data from the Galileo Probe, collected during its descent into Jupiter's
atmosphere, is used to obtain a vertical profile of the zonal wind from
$\mathbf{\sim 0.5}$ bar (upper troposphere) to $\mathbf{\sim 0.1\, \mu{bar}}$
(lower thermosphere) at the probe entry site. This is accomplished by
constructing a map of gravity wave Lomb-Scargle periodograms as a function of
altitude. The profile obtained from the map indicates that the wind speed above
the visible cloud deck increases with height to $\mathbf{\sim 150}$
m\,s$\mathbf{^{-1}}$ and then levels off at this value over a broad altitude
range. The location of the turbopause, as a region of wide wave spectrum, is
also identified from the map. In addition, a cross-equatorial oscillation of a
jet, which has previously been linked to the quasi-quadrennial oscillation in
the stratosphere, is suggested by the profile. | astro-ph_EP |
55 Cancri: A Coplanar Planetary System that is Likely Misaligned with
its Star: Although the 55 Cnc system contains multiple, closely packed planets that are
presumably in a coplanar configuration, we use numerical simulations to
demonstrate that they are likely to be highly inclined to their parent star's
spin axis. Due to perturbations from its distant binary companion, this
planetary system precesses like a rigid body about its parent star.
Consequently, the parent star's spin axis and the planetary orbit normal likely
diverged long ago. Because only the projected separation of the binary is
known, we study this effect statistically, assuming an isotropic distribution
for wide binary orbits. We find that the most likely projected spin-orbit angle
is ~50 degrees, with a ~30% chance of a retrograde configuration. Transit
observations of the innermost planet - 55 Cnc e - may be used to verify these
findings via the Rossiter-McLaughlin effect. 55 Cancri may thus represent a new
class of planetary systems with well-ordered, coplanar orbits that are inclined
with respect to the stellar equator. | astro-ph_EP |
Observability of substructures in planet-forming disk in (sub)cm
wavelength with SKA and ngVLA: Current imaging observations of protoplanetary disks using ALMA primarily
focus on the sub-millimeter wavelength, leaving a gap in effective
observational approaches for centimeter-sized dust, which is crucial to the
issue of planet formation. The forthcoming SKA and ngVLA may rectify this
deficiency. In this paper, we employ multi-fluid hydrodynamic numerical
simulations and radiative transfer calculations to investigate the potential of
SKA1-Mid, ngVLA, and SKA2 for imaging protoplanetary disks at sub-cm/cm
wavelengths. We create mock images with ALMA/SKA/ngVLA at multi-wavelengths
based on the hydrodynamical simulation output, and test different sensitivity
and spatial resolutions. We discover that both SKA and ngVLA will serve as
excellent supplements to the existing observational range of ALMA, and their
high resolution enables them to image substructures in the disk's inner region
($\sim$ 5 au from the stellar). Our results indicate that SKA and ngVLA can be
utilized for more extended monitoring programs in the centimeter waveband.
While in the sub-centimeter range, ngVLA possesses the capability to produce
high-fidelity images within shorter observation times ($\sim$ 1 hour on source
time) than previous research, holding potential for future survey observations.
We also discuss for the first time the potential of SKA2 for observing
protoplanetary disks at a 0.7 cm wavelength. | astro-ph_EP |
Persephone: A Pluto-System Orbiter and Kuiper Belt Explorer: Persephone is a NASA concept mission study that addresses key questions
raised by New Horizons' encounters with Kuiper Belt objects (KBOs), with
arguably the most important being "Does Pluto have a subsurface ocean?". More
broadly, Persephone would answer four significant science questions: (1) What
are the internal structures of Pluto and Charon? (2) How have the surfaces and
atmospheres in the Pluto system evolved? (3) How has the KBO population
evolved? (4) What are the particles and magnetic field environments of the
Kuiper Belt? To answer these questions, Persephone has a comprehensive payload,
and would both orbit within the Pluto system and encounter other KBOs. The
nominal mission is 30.7 years long, with launch in 2031 on a Space Launch
System (SLS) Block 2 rocket with a Centaur kick stage, followed by a 27.6 year
cruise powered by existing radioisotope electric propulsion (REP) and a Jupiter
gravity assist to reach Pluto in 2058. En route to Pluto, Persephone would have
one 50- to 100-km-class KBO encounter before starting a 3.1 Earth-year orbital
campaign of the Pluto system. The mission also includes the potential for an
8-year extended mission, which would enable the exploration of another KBO in
the 100- to 150-km-size class. The mission payload includes 11 instruments:
Panchromatic and Color High-Resolution Imager; Low-Light Camera; Ultra-Violet
Spectrometer; Near-Infrared (IR) Spectrometer; Thermal IR Camera; Radio
Frequency Spectrometer; Mass Spectrometer; Altimeter; Sounding Radar;
Magnetometer; and Plasma Spectrometer. The nominal cost of this mission is
$3.0B, making it a large strategic science mission. | astro-ph_EP |
Chemical abundances of neutron capture elements in exoplanet-hosting
stars: To understand the formation and composition of planetary systems it is
important to study their host stars composition since both are formed in the
same stellar nebula. In this work we analyze the behaviour of chemical
abundances of Cu, Zn, Sr, Y, Zr, Ba, Ce, Nd and Eu in the large and homogeneous
HARPS-GTO planet search sample ($R \sim$ 115000). This sample is composed of
120 stars hosting high-mass planets, 29 stars hosting exclusively Neptunians
and Super-Earths and 910 stars without detected giant planets. We compare the
[X/Fe] ratios of such elements in different metallicity bins and we find that
planet hosts present higher abundances of Zn for [Fe/H]$<$--0.1 dex. On the
other hand, Ba, Sr, Ce and Zr abundances are underabundant in stars with
planets, with a bigger difference for stars only hosting low-mass planets.
However, most of the offsets found can be explained by differences in stellar
parameters and by the fact that planet hosts at low metallicity mostly belong
to the Galactic thick disk. Only in the case of Ba we find a statistically
significant (3$\sigma$) underabundance of 0.03 dex for low-mass planet hosts.
The origin of these elements is quite complex due to their evolution during the
history of the Galaxy. Therefore, it is necessary to understand and
characterize the stellar populations to which planet hosts belong in order to
do a fair comparison with stars without detected planets. This work
demonstrates that the effects of Galactic chemical evolution and not the
presence of planets mostly account for the differences we find. | astro-ph_EP |
Tidal dissipation in multi-planet systems and constraints to
orbit-fitting: We present here in full details the linear secular theory with tidal damping
that was used to constraint the fit of the HD10180 planetary system in (Lovis
et al. 2011). The theory is very general and can provide some intuitive
understanding of the final state of a planetary system when one or more planets
are close to their central star. We globally recover the results of (Mardling
2007), but we show that in the HD209458 planetary system, the consideration of
the tides raised by the central star on the planet lead to believe that the
eccentricity of HD209458b is most probably much smaller than 0.01. | astro-ph_EP |
Telling twins apart: Exo-Earths and Venuses with transit spectroscopy: The planned launch of the James Webb Space Telescope in 2018 will herald a
new era of exoplanet spectroscopy. JWST will be the first telescope sensitive
enough to potentially characterize terrestrial planets from their transmission
spectra. In this work, we explore the possibility that terrestrial planets with
Venus-type and Earth-type atmospheres could be distinguished from each other
using spectra obtained by JWST. If we find a terrestrial planet close to the
liquid water habitable zone of an M5 star within a distance of 10 parsecs, it
would be possible to detect atmospheric ozone if present in large enough
quantities, which would enable an oxygen-rich atmosphere to be identified.
However, the cloudiness of a Venus-type atmosphere would inhibit our ability to
draw firm conclusions about the atmospheric composition, making any result
ambiguous. Observing small, temperate planets with JWST requires significant
investment of resources, with single targets requiring of order 100 transits to
achieve sufficient signal to noise. The possibility of detecting a crucial
feature such as the ozone signature would need to be carefully weighed against
the likelihood of clouds obscuring gas absorption in the spectrum. | astro-ph_EP |
Obliquity evolution of the minor satellites of Pluto and Charon: New Horizons mission observations show that the small satellites Styx, Nix,
Kerberos and Hydra, of the Pluto-Charon system, have not tidally spun-down to
near synchronous spin states and have high obliquities with respect to their
orbit about the Pluto-Charon binary (Weaver et al. 2016). We use a damped
mass-spring model within an N-body simulation to study spin and obliquity
evolution for single spinning non-round bodies in circumbinary orbit.
Simulations with tidal dissipation alone do not show strong obliquity
variations from tidally induced spin-orbit resonance crossing and this we
attribute to the high satellite spin rates and low orbital eccentricities.
However, a tidally evolving Styx exhibits intermittent obliquity variations and
episodes of tumbling. During a previous epoch where Charon migrated away from
Pluto, the minor satellites could have been trapped in orbital mean motion
inclination resonances. An outward migrating Charon induces large variations in
Nix and Styx's obliquities. The cause is a commensurability between the mean
motion resonance frequency and the spin precession rate of the spinning body.
As the minor satellites are near mean motion resonances, this mechanism could
have lifted the obliquities of all four minor satellites. The high obliquities
need not be primordial if the minor satellites were at one time captured into
mean motion resonances. | astro-ph_EP |
Growth and Evolution of Secondary Volcanic Atmospheres: II. The
Importance of Kinetics: Volcanism is a major and long-term source of volatile elements such as C and
H to Earth's atmosphere, likely has been to Venus's atmosphere, and may be for
exoplanets. Models simulating volcanic growth of atmospheres often make one of
two assumptions: either that atmospheric speciation is set by the
high-temperature equilibrium of volcanism; or, that volcanic gases
thermochemically re-equilibrate to the new, lower, temperature of the surface
environment. In the latter case it has been suggested that volcanic atmospheres
may create biosignature false positives. Here, we test the assumptions
underlying such inferences by performing chemical kinetic calculations to
estimate the relaxation timescale of volcanically-derived atmospheres to
thermochemical equilibrium, in a simple 0D atmosphere neglecting photochemistry
and reaction catalysis. We demonstrate that for planets with volcanic
atmospheres, thermochemical equilibrium over geological timescales can only be
assumed if the atmospheric temperature is above ~700K. Slow chemical kinetics
at lower temperatures inhibit the relaxation of redox-sensitive species to
low-temperature thermochemical equilibrium, precluding the production of two
independent biosignatures through thermochemistry alone: 1. ammonia, and 2. the
co-occurrence of CO$_2$ and CH$_4$ in an atmosphere in the absence of CO. This
supports the use of both biosignatures for detecting life. Quenched at the high
temperature of their degassing, volcanic gases also have speciations
characteristic of those produced from a more oxidized mantle, if interpreted as
being at thermochemical equilibrium. This therefore complicates linking
atmospheres to the interiors of rocky exoplanets, even when their atmospheres
are purely volcanic in origin. | astro-ph_EP |
A Gaussian process framework for modelling instrumental systematics:
application to transmission spectroscopy: Transmission spectroscopy, which consists of measuring the
wavelength-dependent absorption of starlight by a planet's atmosphere during a
transit, is a powerful probe of atmospheric composition. However, the expected
signal is typically orders of magnitude smaller than instrumental systematics,
and the results are crucially dependent on the treatment of the latter. In this
paper, we propose a new method to infer transit parameters in the presence of
systematic noise using Gaussian processes, a technique widely used in the
machine learning community for Bayesian regression and classification problems.
Our method makes use of auxiliary information about the state of the
instrument, but does so in a non-parametric manner, without imposing a specific
dependence of the systematics on the instrumental parameters, and naturally
allows for the correlated nature of the noise. We give an example application
of the method to archival NICMOS transmission spectroscopy of the hot Jupiter
HD 189733, which goes some way towards reconciling the controversy surrounding
this dataset in the literature. Finally, we provide an appendix giving a
general introduction to Gaussian processes for regression, in order to
encourage their application to a wider range of problems. | astro-ph_EP |
Physical Parameters of Asteroids Estimated from the WISE 3 Band Data and
NEOWISE Post-Cryogenic Survey: Enhancements to the science data processing pipeline of NASA's Wide-field
Infrared Explorer (WISE) mission, collectively known as NEOWISE, resulted in
the detection of $>$158,000 minor planets in four infrared wavelengths during
the fully cryogenic portion of the mission. Following the depletion of its
cryogen, NASA's Planetary Science Directorate funded a four month extension to
complete the survey of the inner edge of the Main Asteroid Belt and to detect
and discover near-Earth objects (NEOs). This extended survey phase, known as
the NEOWISE Post-Cryogenic Survey, resulted in the detection of $\sim$6500
large Main Belt asteroids and 88 NEOs in its 3.4 and 4.6 $\mu$m channels.
During the Post-Cryogenic Survey, NEOWISE discovered and detected a number of
asteroids co-orbital with the Earth and Mars, including the first known Earth
Trojan. We present preliminary thermal fits for these and other NEOs detected
during the 3-Band Cryogenic and Post-Cryogenic Surveys. | astro-ph_EP |
Millimeter Gap Contrast as a Probe for Turbulence Level in
Protoplanetary Disks: Turbulent motions are believed to regulate angular momentum transport and
influence dust evolution in protoplanetary disks. Measuring the strength of
turbulence is challenging through gas line observations because of the
requirement for high spatial and spectral resolution data, and an exquisite
determination of the temperature. In this work, taking the well-known HD 163296
disk as an example, we investigated the contrast of gaps identified in high
angular resolution continuum images as a probe for the level of turbulence.
With self-consistent radiative transfer models, we simultaneously analyzed the
radial brightness profiles along the disk major and minor axes, and the
azimuthal brightness profiles of the B67 and B100 rings. By fitting all the gap
contrasts measured from these profiles, we constrained the gas-to-dust scale
height ratio $\Lambda$ to be $3.0_{-0.8}^{+0.3}$, $1.2_{-0.1}^{+0.1}$ and
${\ge}\,6.5$ for the D48, B67 and B100 regions, respectively. The varying
gas-to-dust scale height ratios indicate that the degree of dust settling
changes with radius. The inferred values for $\Lambda$ translate into a
turbulence level of $\alpha_{\rm turb}\,{<}\,3\times10^{-3}$ in the D48 and
B100 regions, which is consistent with previous upper limits set by gas line
observations. However, turbulent motions in the B67 ring are strong with
$\alpha_{\rm turb}\,{\sim}1.2\,{\times}\,10^{-2}$. Due to the degeneracy
between $\Lambda$ and the depth of dust surface density drops, the turbulence
strength in the D86 gap region is not constrained. | astro-ph_EP |
Common 0.1 bar Tropopause in Thick Atmospheres Set by Pressure-Dependent
Infrared Transparency: A minimum atmospheric temperature, or tropopause, occurs at a pressure of
around 0.1 bar in the atmospheres of Earth, Titan, Jupiter, Saturn, Uranus and
Neptune, despite great differences in atmospheric composition, gravity,
internal heat and sunlight. In all these bodies, the tropopause separates a
stratosphere with a temperature profile that is controlled by the absorption of
shortwave solar radiation, from a region below characterised by convection,
weather, and clouds. However, it is not obvious why the tropopause occurs at
the specific pressure near 0.1 bar. Here we use a physically-based model to
demonstrate that, at atmospheric pressures lower than 0.1 bar, transparency to
thermal radiation allows shortwave heating to dominate, creating a
stratosphere. At higher pressures, atmospheres become opaque to thermal
radiation, causing temperatures to increase with depth and convection to ensue.
A common dependence of infrared opacity on pressure, arising from the shared
physics of molecular absorption, sets the 0.1 bar tropopause. We hypothesize
that a tropopause at a pressure of approximately 0.1 bar is characteristic of
many thick atmospheres, including exoplanets and exomoons in our galaxy and
beyond. Judicious use of this rule could help constrain the atmospheric
structure, and thus the surface environments and habitability, of exoplanets. | astro-ph_EP |
Submillimeter Array Observations of the RX J1633.9-2442 Transition Disk:
Evidence for Multiple Planets in the Making: We present continuum high resolution Submillimeter Array (SMA) observations
of the transition disk object RX J1633.9-2442, which is located in the
Ophiuchus molecular cloud and has recently been identified as a likely site of
ongoing giant planet formation. The observations were taken at 340 GHz (880
micron) with the SMA in its most extended configuration, resulting in an
angular resolution of 0.3" (35 AU at the distance of the target). We find that
the disk is highly inclined (i ~50 deg) and has an inner cavity ~25 AU in
radius, which is clearly resolved by our observations. We simultaneously model
the entire optical to millimeter wavelength spectral energy distribution (SED)
and SMA visibilities of RX J1633.9-2442 in order to constrain the structure of
its disk. We find that an empty cavity ~25 AU in radius is inconsistent with
the excess emission observed at 12, 22, and 24 micron. Instead, the mid-IR
excess can be modeled by either a narrow, optically thick ring at ~10 AU or an
optically thin region extending from ~7 AU to ~25 AU. The inner disk (r < 5 AU)
is mostly depleted of small dust grains as attested by the lack of detectable
near-IR excess. We also present deep Keck aperture masking observations in the
near-IR, which rule out the presence of a companion up to 500 times fainter
than the primary star (in K-band) for projected separations in the 5-20 AU
range. We argue that the complex structure of the RX J1633.9-2442 disk is best
explained by multiple planets embedded within the disk. We also suggest that
the properties and incidence of objects such as RX J1633.9-2442, T Cha, and
LkCa 15 (and those of the companions recently identified to these two latter
objects) are most consistent with the runaway gas accretion phase of the core
accretion model, when giant planets gain their envelopes and suddenly become
massive enough to open wide gaps in the disk. | astro-ph_EP |
Combining high-dispersion spectroscopy (HDS) with high contrast imaging
(HCI): Probing rocky planets around our nearest neighbors: Aims: In this work, we discuss a way to combine High Dispersion Spectroscopy
and High Contrast Imaging (HDS+HCI). For a planet located at a resolvable
angular distance from its host star, the starlight can be reduced up to several
orders of magnitude using adaptive optics and/or coronography. In addition, the
remaining starlight can be filtered out using high-dispersion spectroscopy,
utilizing the significantly different (or Doppler shifted) high-dispersion
spectra of the planet and star. In this way, HDS+HCI can in principle reach
contrast limits of ~1e-5 x 1e-5, although in practice this will be limited by
photon noise and/or sky-background.
Methods: We present simulations of HDS+HCI observations with the E-ELT, both
probing thermal emission from a planet at infrared wavelengths, and starlight
reflected off a planet atmosphere at optical wavelengths. For the infrared
simulations we use the baseline parameters of the E-ELT and METIS instrument,
with the latter combining extreme adaptive optics with an R=100,000 IFS. We
include realistic models of the adaptive optics performance and atmospheric
transmission and emission. For the optical simulation we also assume R=100,000
IFS with adaptive optics capabilities at the E-ELT.
Results: One night of HDS+HCI observations with the E-ELT at 4.8 um (d_lambda
= 0.07 um) can detect a planet orbiting alpha Cen A with a radius of R=1.5
R_earth and a twin-Earth thermal spectrum of T_eq=300 K at a signal-to-noise
(S/N) of 5. In the optical, with a Strehl ratio performance of 0.3, reflected
light from an Earth-size planet in the habitable zone of Proxima Centauri can
be detected at a S/N of 10 in the same time frame. Recently, first HDS+HCI
observations have shown the potential of this technique by determining the
spin-rotation of the young massive exoplanet beta Pictoris b. [abridged] | astro-ph_EP |
High-precision photometry by telescope defocussing. I. The transiting
planetary system WASP-5: We present high-precision photometry of two transit events of the extrasolar
planetary system WASP-5, obtained with the Danish 1.54m telescope at ESO La
Silla. In order to minimise both random and flat-fielding errors, we defocussed
the telescope so its point spread function approximated an annulus of diameter
40 pixels (16 arcsec). Data reduction was undertaken using standard aperture
photometry plus an algorithm for optimally combining the ensemble of comparison
stars. The resulting light curves have point-to-point scatters of 0.50 mmag for
the first transit and 0.59 mmag for the second. We construct detailed signal to
noise calculations for defocussed photometry, and apply them to our
observations. We model the light curves with the JKTEBOP code and combine the
results with tabulated predictions from theoretical stellar evolutionary models
to derive the physical properties of the WASP-5 system. We find that the planet
has a mass of M_b = 1.637 +/- 0.075 +/- 0.033 Mjup, a radius of R_b = 1.171 +/-
0.056 +/- 0.012 Rjup, a large surface gravity of g_b = 29.6 +/- 2.8 m/s2 and a
density of rho_b = 1.02 +/- 0.14 +/- 0.01 rhojup (statistical and systematic
uncertainties). The planet's high equilibrium temperature of T_eq = 1732 +/- 80
K makes it a good candidate for detecting secondary eclipses. | astro-ph_EP |
A LOOK at Outbursts of Comet C/2014 UN$_{271}$ (Bernardinelli-Bernstein)
Near 20 au: Cometary activity may be driven by ices with very low sublimation
temperatures, such as carbon monoxide ice, which can sublimate at distances
well beyond 20 au. This point is emphasized by the discovery of Oort cloud
comet C/2014 UN$_{271}$ (Bernardinelli-Bernstein), and its observed activity
out to $\sim$26 au. Through observations of this comet's optical brightness and
behavior, we can potentially discern the drivers of activity in the outer solar
system. We present a study of the activity of comet Bernardinelli-Bernstein
with broad-band optical photometry taken at 19-20 au from the Sun (2021 June to
2022 February) as part of the LCO Outbursting Objects Key (LOOK) Project. Our
analysis shows that the comet's optical brightness during this period was
initially dominated by cometary outbursts, stochastic events that ejected
$\sim10^7$ to $\sim10^8$ kg of material on short (< 1 day) timescales. We
present evidence for three such outbursts occurring in 2021 June and September.
The nominal nuclear volumes excavated by these events are similar to the 10-100
m pit-shaped voids on the surfaces of short-period comet nuclei, as imaged by
spacecraft. Two out of three Oort cloud comets observed at large pre-perihelion
distances exhibit outburst behavior near 20 au, suggesting such events may be
common in this population. In addition, quiescent CO-driven activity may
account for the brightness of the comet in 2022 January to February, but that
variations in the cometary active area (i.e., the amount of sublimating ice)
with heliocentric distance are also possible. | astro-ph_EP |
Constraints on Planet Occurrence around Nearby Mid-to-Late M Dwarfs from
the MEarth Project: The MEarth Project is a ground-based photometric survey to find planets
transiting the closest and smallest main-sequence stars. In its first four
years, MEarth discovered one transiting exoplanet, the 2.7 Earth radius planet
GJ1214b. Here, we answer an outstanding question: in light of the bounty of
small planets transiting small stars uncovered by the Kepler mission, should
MEarth have found more than just one planet so far? We estimate MEarth's
ensemble sensitivity to exoplanets by performing end-to-end simulations of 1.25
million observations of 988 nearby mid-to-late M dwarfs, gathered by MEarth
between October 2008 and June 2012. For 2-4 Earth radius planets, we compare
this sensitivity to results from Kepler and find that MEarth should have found
planets at a rate of 0.05 - 0.36 planets/year in its first four years. As part
of this analysis, we provide new analytic fits to the Kepler early M dwarf
planet occurrence distribution. When extrapolating between Kepler's early M
dwarfs and MEarth's mid-to-late M dwarfs, we find that assuming the planet
occurrence distribution stays fixed with respect to planetary equilibrium
temperature provides a good match to our detection of a planet with GJ1214b's
observed properties. For larger planets, we find that the warm (600-700K),
Neptune-sized (4 Earth radius) exoplanets that transit early M dwarfs like
Gl436 and GJ3470 occur at a rate of <0.15/star (at 95% confidence) around
MEarth's later M dwarf targets. We describe a strategy with which MEarth can
increase its expected planet yield by 2.5X without new telescopes, by shifting
its sensitivity toward the smaller and cooler exoplanets that Kepler has
demonstrated to be abundant. | astro-ph_EP |
Formation of giant planets with large metal masses and metal fractions
via giant impacts in a rapidly dissipating disk: According to planetary interior models, some giant planets contain large
metal masses with large metal-mass fractions. HD 149026b and TOI-849b are
characteristic examples of these giant planets. It has been suggested that the
envelope mass loss during giant impacts plays a key role in the formation of
such giant planets. The aim of the present letter is to propose a mechanism
that can explain the origin of such giant planets. We investigate the formation
of giant planets in a rapidly dissipating disk using N-body simulations that
consider pebble accretion. The results show that although the pebble isolation
mass is smaller than the metal mass (> 30 Earth masses) in some giant planets,
the interior metal mass can be increased by giant impacts between planets with
the isolation mass. Regarding the metal fraction, the cores accrete massive
envelopes by runaway gas accretion during the disk-dissipation phase of 1-10
Myr in a disk that evolves without photoevaporation. Although a large fraction
of the envelope can be lost during giant impacts, the planets can reaccrete the
envelope after impacts in a slowly dissipating disk. Here, we demonstrate that,
by photoevaporation in a rapidly dissipating disk, the runaway gas accretion is
quenched in the middle, resulting in the formation of giant planets with large
metal-mass fractions. The origins of HD 149026b and TOI-849b, which are
characterized by their large metal-mass fractions, can be naturally explained
by a model that considers a disk evolving with photoevaporation. | astro-ph_EP |
The Hubble PanCET program: An extensive search for metallic ions in the
exosphere of GJ 436 b: (Abridged) The quiet M2.5 star GJ 436 hosts a warm Neptune that displays an
extended atmosphere that dwarfs its own host star. Predictions of atmospheric
escape in such planets state that H atoms escape from the upper atmosphere in a
collisional regime and that the flow can drag heavier atoms to the upper
atmosphere. It is unclear, however, what astrophysical mechanisms drive the
process. Our objective is to leverage the extensive coverage of HST/COS
observations of the far-ultraviolet (FUV) spectrum of GJ 436 to search for
signals of metallic ions in the upper atmosphere of GJ 436 b. We analyzed flux
time-series of species present in the FUV spectrum of GJ 436, as well as the
Lyman-$\alpha$ line. GJ 436 displays FUV flaring events with a rate of $\sim$10
d$^{-1}$. There is evidence for a possibly long-lived active region or
longitude that modulates the FUV metallic lines of the star with amplitudes up
to 20%. Despite the strong geocoronal contamination in the COS spectra, we
detected in-transit excess absorption signals of $\sim$50% and $\sim$30% in the
blue and red wings, respectively, of the Lyman-$\alpha$ line. We rule out a
wide range of excess absorption levels in the metallic lines of the star during
the transit. The large atmospheric loss of GJ 436 b observed in Lyman-$\alpha$
transmission spectra is stable over the timescale of a few years, and the red
wing signal supports the presence of a variable hydrogen absorption source
besides the stable exosphere. The previously claimed in-transit absorption in
the Si III line is likely an artifact resulting from the stellar magnetic
cycle. The non-detection of metallic ions in absorption could indicate that the
escape is not hydrodynamic or that the atmospheric mixing is not efficient in
dragging metals high enough for sublimation to produce a detectable escape rate
of ions to the exosphere. | astro-ph_EP |
Five Special Types of Orbits Around Mars: The abstract is additional with repect to the paper published in JGCD.
Ordinary Earth satellites are usually placed into five categories of special
orbits: sun-synchronous orbits, orbits at the critical inclination, frozen
orbits, repeating ground track orbits, and geostationary orbits. This paper
investigates their counterparts around Mars and examines the basic nature of
these orbits, which are of special interest for missions conducted around Mars,
including Mars reconnaissance. Mars' gravity field is much more complicated,
with relatively smaller J2, compared to Earth's, which makes the behaviors of
these Martian orbits different from those of Earth. Analytical formulations and
numerical simulations are used to analyze these Martian orbits and compare them
with their Earth counterparts. First, mean element theory is employed to
describe variations of orbital elements and give the constraint conditions for
achieving these special orbits. Then, numerical verifications based on the
PSODE algorithm (particle swarm optimization combined with differential
evolution) are adopted to provide more accurate conditions for achieving these
orbits when considering an Mars gravity field. Using the numerical method can
significantly improve the design in the full gravity field, and it is therefore
possible to select these usable orbits for Mars that can reduce or eliminate
the need for stationkeeping. | astro-ph_EP |
Wind-Enhanced Interaction of Radiation and Dust (WEIRD) and the Growth
and Maintenance of Local Dust Storms on Mars: A radiative-dynamic positive feedback mechanism (Wind Enhanced Interaction of
Radiation and Dust: WEIRD) for localized Mars dust disturbances was previously
found to operate in highly idealized numerical experiments. Numerical
simulations are used to test for the presence and quantitative effect of the
radiative-dynamic WEIRD feedback mechanism under more realistic conditions.
Comparisons between cases where lifted dust is radiatively active and
radiatively passive elucidate the importance of the dust radiative forcing on
the thermodynamic and kinematic structure of the atmosphere. The WEIRD feedback
mechanism does operate under realistic conditions, although it can be masked
and diminished by a variety of other forcing mechanisms. Globally increased
dust loading is found to accelerate the local winds while simultaneously
diminishing the impact of local physiographical forcing. Local enhancements of
dust produce a thermal and dynamical response that resembles many of the
essential features seen in the idealized experiments. The development of a warm
core low, rotational wind tendencies and convergence boundaries intersecting at
the center of the strongest dust storms are consistent with WEIRD. Local and
regional storms are effective at producing elevated dust layers above the
boundary layer aided by the radiative forcing of the dust. Ubiquitous and
persistent thermal circulations associated with topography can also inject dust
into the free atmosphere above the planetary boundary layer, but they are less
efficient than the dust storms. High concentrations of dust in the lowest
levels of the atmosphere produce a significant and dramatic heating of the
ground and the near-surface air despite greatly reduced insolation at the
surface. | astro-ph_EP |
Deserts and pile-ups in the distribution of exoplanets due to
photoevaporative disc clearing: We present models of giant planet migration in evolving protoplanetary discs.
We show that disc clearing by EUV photoevaporation can have a strong effect on
the distribution of giant planet semi-major axes. During disc clearing planet
migration is slowed or accelerated in the region where photoevaporation opens a
gap in the disc, resulting in "deserts" where few giant planets are found and
corresponding "pile-ups" at smaller and larger radii. However, the precise
locations and sizes of these features are strong functions of the efficiency of
planetary accretion, and therefore also strongly dependent on planet mass. We
suggest that photoevaporative disc clearing may be responsible for the pile-up
of ~Jupiter-mass planets at ~1AU seen in exoplanet surveys, and show that
observations of the distribution of exoplanet semi-major axes can be used to
test models of both planet migration and disc clearing. | astro-ph_EP |
Long-Term Cycling of Kozai-Lidov Cycles: Extreme Eccentricities and
Inclinations Excited by a Distant Eccentric Perturber: Kozai-Lidov oscillations of Jupiter-mass planets, excited by comparable
planetary or brown dwarf mass perturbers were recently shown in numerical
experiments to be slowly modulated and to exhibit striking features, including
extremely high eccentricities and the generation of retrograde orbits with
respect to the perturber. Here we solve this problem analytically for the case
of a test particle orbiting a host star and perturbed by a distant companion
whose orbit is eccentric and highly inclined. We give analytic expressions for
the conditions that produce retrograde orbits and high eccentricities. This
mechanism likely operates in various systems thought to involve Kozai-Lidov
oscillations such as tight binaries, mergers of compact objects, irregular
moons of planets and many others. In particular, it could be responsible for
exciting eccentricities and inclinations of exo-planetary orbits and be
important for understanding the spin-orbit (mis)alignment of hot Jupiters. | astro-ph_EP |
Refined Parameters of Chelyabinsk and Tunguska Meteoroids and their
Explosion Modes: This paper describes application of mathematical model that establishes
relationship between parameters of celestial bodies motion in the spheres of
activity of the Sun and the Earth with mass-energy characteristics of these
objects and their explosion modes during destruction in the Earth atmosphere,
that in turn are linked with phenomena observed on underlying surface. This
model was used to calculate the characteristics of objects that caused the
Chelyabinsk and Tunguska explosions with using of its trajectory parameters
described in recent scientific publications (late 2013 - early 2014). It turned
out that the size of Chelyabinsk meteoroid was equal to 180 - 185 meters, and
its mass was close to 1.8 megatons. Energy of its explosion was equal to 57
megatons of TNT, size of Tunguska meteoroid was equal to 105 m, mass - 0.35
megatons, while energy of explosion was about of 14.5 megatons of TNT. Due to
the common origin of these two celestial bodies their average density was equal
- about of 570 kg/m^3. | astro-ph_EP |
Elimination of a virtual impactor of 2006 QV89 via deep non-detection: As a consequence of the large (and growing) number of near-Earth objects
discovered, some of them are lost before their orbit can be firmly established
to ensure long-term recovery. A fraction of these present non-negligible
chances of impact with the Earth. We present a method of targeted observations
that allowed us to eliminate that risk by obtaining deep images of the area
where the object would be, should it be on a collision orbit. 2006 QV89 was one
of these objects, with a chance of impact with the Earth on 2019 September 9.
Its position uncertainty (of the order of 1 degree) and faintness (below
V$\sim$24) made it a difficult candidate for a traditional direct recovery.
However, the position of the virtual impactors could be determined with
excellent accuracy. In July 2019, the virtual impactors of 2006 QV89 were
particularly well placed, with a very small uncertainty region, and an expected
magnitude of V$<$26. The area was imaged using ESO's Very Large Telescope, in
the context of the ESA/ESO collaboration on Near-Earth Objects, resulting in
very constraining a non-detection. This resulted in the elimination of the
virtual impactor, even without effectively recovering 2006 QV89, indicating
that it did not represent a threat. This method of deep non-detection of
virtual impactors demonstrated a large potential to eliminate the threat of
other-wise difficult to recover near-Earth objects | astro-ph_EP |
Misaligned And Alien Planets From Explosive Death Of Stars: Exoplanets whose orbit is misaligned with the spin of their host star could
have originated from high-speed gas blobs, which are observed in multitudes in
nearby supernova remnants and planetary nebulae. These blobs grow in mass and
slow down in the interstellar medium (ISM) by mass accretion and cool by
radiation. If their mass exceeds the Jeans mass, they collapse into hot giant
gas planets. Most of the 'missing baryons' in galaxies could have been swept
into such free-floating objects, which could perturb stellar planetary systems,
kick bound planets into misaligned orbits or be captured themselves into
misaligned orbits. The uncollapsed ones can then collapse or be tidally
disrupted into a tilted gas disk where formation of misaligned planets can take
place. Giant gas planets free floating in the Galactic ISM may be detected by
their microlensing effects or by deep photometry if they are hot. The
uncollapsed gas blobs may produce the observed radio scintillations of comact
extragalactic radio sources such as quasars and gamma ray bursts. | astro-ph_EP |
Dust Formation in Astrophysical Environments: The Importance of Kinetics: Astronomical observations and analysis of stardust isolated from meteorites
have revealed a highly diverse interstellar and circumstellar grain inventory,
including a wide range of amorphous materials and crystalline compounds
(silicates and carbon). This diversity reflects the wide range of stellar
sources injecting solids into the interstellar medium each with its own
physical characteristics such as density, temperature and elemental composition
and highlights the importance of kinetics rather than thermodynamics in the
formation of these compounds. Based upon the extensive literature on soot
formation in terrestrial settings, detailed kinetic pathways have been
identified for the formation of carbon dust in C-rich stellar ejecta. These
have been incorporated in astronomical models for these environments. In recent
years, the chemical routes in the nucleation of oxides and silicates have been
the focus of much astronomical research. These aspects of stardust formation
will be reviewed and lessons for dust formation in planetary atmospheres will
be drawn with the emphasis on the influence of kinetics on the characteristics
and structure of dust in these environments. | astro-ph_EP |
Tidal dissipation and the formation of Kepler near-resonant planets: Multi-planetary systems detected by the Kepler mission present an excess of
planets close to first-order mean-motion resonances (2:1 and 3:2) but with a
period ratio slightly higher than the resonant value. Several mechanisms have
been proposed to explain this observation. Here we provide some clues that
these near-resonant systems were initially in resonance and reached their
current configuration through tidal dissipation. The argument that has been
opposed to this scenario is that it only applies to the close-in systems and
not to the farthest ones for which the tidal effect is too weak. Using the
catalog of KOI of the Kepler mission, we show that the distributions of period
ratio among the most close-in planetary systems and the farthest ones differ
significantly. This distance dependent repartition is a strong argument in
favor of the tidal dissipation scenario. | astro-ph_EP |
29P/Schwassmann-Wachmann: A Rosetta Stone for Amorphous Water Ice and CO
<-> CO2 Conversion in Centaurs and Comets?: Centaur 29P/Schwassmann-Wachmann 1 (SW1) is a highly active object orbiting
in the transitional Gateway region (Sarid et al. 2019) between the Centaur and
Jupiter Family Comet regions. SW1 is unique among the Centaurs in that it
experiences quasi-regular major outbursts and produces CO emission
continuously; however, the source of the CO is unclear. We argue that due to
its very large size (approx. 32 km radius), SW1 is likely still responding, via
amorphous water ice (AWI) conversion to crystalline water ice (CWI), to the
rapid change in its external thermal environment produced by its dynamical
migration from the Kuiper belt to the Gateway Region at the inner edge of the
Centaur region at 6 au. It is this conversion process that is the source of the
abundant CO and dust released from the object during its quiescent and outburst
phases. If correct, these arguments have a number of important predictions
testable via remote sensing and in situ spacecraft characterization, including:
the quick release on Myr timescales of CO from AWI conversion for any few
km-scale scattered disk KBO transiting into the inner system; that to date SW1
has only converted between 50 to 65% of its nuclear AWI to CWI; that volume
changes upon AWI conversion could have caused subsidence and cave-ins, but not
significant mass wasting or crater loss on SW1; that SW1s coma should contain
abundant amounts of CWI CO2-rich icy dust particles; and that when SW1 transits
into the inner system within the next 10,000 years, it will be a very different
kind of JFC comet. | astro-ph_EP |
Using Deep Neural Networks to compute the mass of forming planets: Computing the mass of planetary envelopes and the critical mass beyond which
planets accrete gas in a runaway fashion is important when studying planet
formation, in particular for planets up to the Neptune mass range. This
computation requires in principle solving a set of differential equations, the
internal structure equations, for some boundary conditions (pressure,
temperature in the protoplanetary disk where a planet forms, core mass and
accretion rate of solids by the planet). Solving these equations in turn proves
being time consuming and sometimes numerically unstable. We developed a method
to approximate the result of integrating the internal structure equations for a
variety of boundary conditions. We compute a set of planet internal structures
for a very large number (millions) of boundary conditions, considering two
opacities,(ISM and reduced). This database is then used to train Deep Neural
Networks in order to predict the critical core mass as well as the mass of
planetary envelopes as a function of the boundary conditions. We show that our
neural networks provide a very good approximation (at the level of percents) of
the result obtained by solving interior structure equations, but with a much
smaller required computer time. The difference with the real solution is much
smaller than the one obtained using some analytical formulas available in the
literature which at best only provide the correct order of magnitude. We
compare the results of the DNN with other popular machine learning methods
(Random Forest, Gradient Boost, Support Vector Regression) and show that the
DNN outperforms these methods by a factor of at least two. We show that some
analytical formulas that can be found in various papers can severely
overestimate the mass of planets, therefore predicting the formation of planets
in the Jupiter-mass regime instead of the Neptune-mass regime. | astro-ph_EP |
Determination of the Interior Structure of Transiting Planets in
Multiple-Planet Systems: Tidal dissipation within a short-period transiting extrasolar planet
perturbed by a companion object can drive orbital evolution of the system to a
so-called tidal fixed point, in which the apsidal lines of the transiting
planet and its perturber are aligned, and for which variations in the orbital
eccentricities of both planet and perturber are damped out. Significant
contributions to the apsidal precession rate are made by the secular
planet-planet interaction, by general relativity, and by the gravitational
quadropole fields created by the transiting planet's tidal and rotational
distortions. The fixed-point orbital eccentricity of the inner planet is
therefore a strong function of the planet's interior structure. We illustrate
these ideas in the specific context of the recently discovered HAT-P-13
exo-planetary system, and show that one can already glean important insights
into the physical properties of the inner transiting planet. We present
structural models of the planet, which indicate that its observed radius can be
maintained for a one-parameter sequence of models that properly vary core mass
and tidal energy dissipation in the interior. We use an octopole-order secular
theory of the orbital dynamics to derive the dependence of the inner planet's
eccentricity, on its tidal Love number. We find that the currently measured
eccentricity, implies 0.116 < k2_{b} < 0.425, 0 M_{Earth}<M_{core}<120
M_{Earth}$, and Q_{b} < 300,000. Improved measurement of the eccentricity will
soon allow for far tighter limits to be placed on all three of these
quantities, and will provide an unprecedented probe into the interior structure
of an extrasolar planet. | astro-ph_EP |
Stability Constrained Characterization of Multiplanet Systems: Many discovered multiplanet systems are tightly packed. This implies that
wide parameter ranges in masses and orbital elements can be dynamically
unstable and ruled out. We present a case study of Kepler-23, a compact
three-planet system where constraints from stability, transit timing variations
(TTVs), and transit durations can be directly compared. We find that in this
tightly packed system, stability can place upper limits on the masses and
orbital eccentricities of the bodies that are comparable to or tighter than
current state of the art methods. Specifically, stability places 68% upper
limits on the orbital eccentricities of 0.09, 0.04, and 0.05 for planets $b$,
$c$ and $d$, respectively. These constraints correspond to radial velocity
signals $\lesssim 20$ cm/s, are significantly tighter to those from transit
durations, and comparable to those from TTVs. Stability also yields 68% upper
limits on the masses of planets $b$, $c$ and $d$ of 2.2, 16.1, and 5.8
$M_\oplus$, respectively, which were competitive with TTV constraints for the
inner and outer planets. Performing this stability constrained characterization
is computationally expensive with N-body integrations. We show that SPOCK, the
Stability of Planetary Orbital Configurations Klassifier, is able to faithfully
approximate the N-body results over 4000 times faster. We argue that such
stability constrained characterization of compact systems is a challenging
"needle-in-a-haystack" problem (requiring removal of 2500 unstable
configurations for every stable one for our adopted priors) and we offer
several practical recommendations for such stability analyses. | astro-ph_EP |
New insights into temperature-dependent ice properties and their effect
on ice shell convection for icy ocean worlds: Ice shell dynamics are an important control on the habitability of icy ocean
worlds. Here we present a systematic study evaluating the effect of
temperature-dependent material properties on these dynamics. We review the
published thermal conductivity data for ice, which demonstrates that the most
commonly used conductivity model in planetary science represents a lower bound.
We propose a new model for thermal conductivity that spans the temperature
range relevant to the ice shells of ocean worlds. This increases the thermal
conductivity at low temperatures near the surface by about a fifth. We show
that such an increase in thermal conductivity near the cold surface can
stabilizes the ice shell of Europa. Furthermore, we show that including
temperature dependent specific heat capacity decreases the energy stored in the
conductive lid which reduces the response timescale of the ice shell to thermal
perturbations by approximately a third. This may help to explain surface
features such as chaotic terrains that require large additions of energy to the
near-surface ice. | astro-ph_EP |
Revisiting fundamental properties of TiO$_2$ nanoclusters as
condensation seeds in astrophysical environments: The formation of inorganic cloud particles takes place in several atmospheric
environments including those of warm, hot, rocky and gaseous exoplanets, brown
dwarfs, and AGB stars. The cloud particle formation needs to be triggered by
the in-situ formation of condensation seeds since it can not be assumed that
such condensation seeds preexist in these chemically complex gas-phase
environments. We aim to develop a methodology to calculate the thermochemical
properties of clusters as key inputs to model the formation of condensation
nuclei in gases of changing chemical composition. TiO$_2$ is used as benchmark
species for cluster sizes N = 1 - 15. We create 90000 candidate geometries, for
cluster sizes N = 3 - 15. We employ a hierarchical optimisation approach,
consisting of a force field description, density functional based tight binding
(DFTB) and all-electron density functional theory (DFT) to obtain accurate
energies and thermochemical properties for the clusters. We find B3LYP/cc-pVTZ
including Grimmes empirical dispersion to perform most accurately with respect
to experimentally derived thermochemical properties of the TiO$_2$ molecule. We
present a hitherto unreported global minimum candidate for size N = 13. The DFT
derived thermochemical cluster data are used to evaluate the nucleation rates
for a given temperature-pressure profile of a model hot Jupiter atmosphere. We
find that with the updated and refined cluster data, nucleation becomes
unfeasible at slightly lower temperatures, raising the lower boundary for seed
formation in the atmosphere. The approach presented in this paper allows to
find stable isomers for small (TiO$_2$)$_N$ clusters. The choice of functional
and basis set for the all-electron DFT calculations have a measurable impact on
the resulting surface tension and nucleation rate and the updated
thermochemical data is recommended for future considerations. | astro-ph_EP |
p-winds: an open-source Python code to model planetary outflows and
upper atmospheres: Atmospheric escape is considered to be one of the main channels for evolution
in sub-Jovian planets, particularly in their early lives. While there are
several hypotheses proposed to explain escape in exoplanets, testing them with
atmospheric observations remains a challenge. In this context, high-resolution
transmission spectroscopy of transiting exoplanets for the metastable helium
triplet (He 2$^3$S) at $1\,083$ nm has emerged as a reliable technique to
observe and measure escape. To aid in the prediction and interpretation of
metastable He transmission spectroscopy observations, we developed the code
p-winds. This is an open-source, fully documented, scalable Python
implementation of the one-dimensional, purely H+He Parker wind model for upper
atmospheres coupled with ionization balance, ray-tracing, and radiative
transfer routines. We demonstrate an atmospheric retrieval by fitting p-winds
models to the observed metastable He transmission spectrum of the warm Neptune
HAT-P-11 b, and take into account the variation of the in-transit absorption
caused by transit geometry. For this planet, our best fit yields a total
atmospheric escape rate of approximately $2.5 \times 10^{10}$ g s$^{-1}$ and
wind temperature of $7200$ K. The range of retrieved mass loss rates increases
significantly when we let the H atom fraction be a free parameter, but the
posterior distribution of the latter remains unconstrained by He observations
alone. The stellar host limb darkening does not have a significant impact in
the retrieved escape rate or outflow temperature for HAT-P-11 b. Based on the
non-detection of escaping He for GJ 436 b, we are able to rule out total escape
rates higher than $3.4 \times 10^{10}$ g s$^{-1}$ at 99.7% (3$\sigma$)
confidence. | astro-ph_EP |
Multiple Spiral Arms in Protoplanetary Disks: Linear Theory: Recent observations of protoplanetary disks, as well as simulations of
planet-disk interaction, have suggested that a single planet may excite
multiple spiral arms in the disk, in contrast to the previous expectations
based on linear theory (predicting a one-armed density wave). We re-assess the
origin of multiple arms in the framework of linear theory, by solving for the
global two-dimensional response of a non-barotropic disk to an orbiting planet.
We show that the formation of a secondary arm in the inner disk, at about half
of the orbital radius of the planet, is a robust prediction of linear theory.
This arm becomes stronger than the primary spiral at several tenths of the
orbital radius of the planet. Several additional, weaker spiral arms may also
form in the inner disk. On the contrary, a secondary spiral arm is unlikely to
form in the outer disk. Our linear calculations, fully accounting for the
global behavior of both the phases and amplitudes of perturbations, generally
support the recently proposed WKB phase argument for the secondary arm origin
(as caused by the intricacy of constructive interference of azimuthal harmonics
of the perturbation at different radii). We provide analytical arguments
showing that the process of a single spiral wake splitting up into multiple
arms is a generic linear outcome of wave propagation in differentially rotating
disks. It is not unique to planet-driven waves and occurs also in linear
calculations of spiral wakes freely propagating with no external torques. These
results are relevant for understanding formation of multiple rings and gaps in
protoplanetary disks. | astro-ph_EP |
Cosmic History and a Candidate Parent Asteroid for the
Quasicrystal-bearing Meteorite Khatyrka: The unique CV-type meteorite Khatyrka is the only natural sample in which
"quasicrystals" and associated crystalline Cu,Al-alloys, including khatyrkite
and cupalite, have been found. They are suspected to have formed in the early
Solar System. To better understand the origin of these exotic phases, and the
relationship of Khatyrka to other CV chondrites, we have measured He and Ne in
six individual, ~40-{\mu}m-sized olivine grains from Khatyrka. We find a
cosmic-ray exposure age of about 2-4 Ma (if the meteoroid was <3 m in diameter,
more if it was larger). The U,Th-He ages of the olivine grains suggest that
Khatyrka experienced a relatively recent (<600 Ma) shock event, which created
pressure and temperature conditions sufficient to form both the quasicrystals
and the high-pressure phases found in the meteorite. We propose that the parent
body of Khatyrka is the large K-type asteroid 89 Julia, based on its peculiar,
but matching reflectance spectrum, evidence for an impact/shock event within
the last few 100 Ma (which formed the Julia family), and its location close to
strong orbital resonances, so that the Khatyrka meteoroid could plausibly have
reached Earth within its rather short cosmic-ray exposure age. | astro-ph_EP |
Physical, spectral, and dynamical properties of asteroid (107) Camilla
and its satellites: The population of large asteroids is thought to be primordial and they are
the most direct witnesses of the early history of our Solar System. Those
satellites allow study of the mass, and hence density and internal structure.
We study here the properties of the triple asteroid (107) Camilla from
lightcurves, stellar occultations, optical spectroscopy, and high-contrast and
high-angular-resolution images and spectro-images. Using 80 positions over 15
years, we determine the orbit of its larger satellite to be circular,
equatorial, and prograde, with RMS residuals of 7.8 mas. From 11 positions in
three epochs only, in 2015 and 2016, we determine a preliminary orbit for the
second satellite. We find the orbit to be somewhat eccentric and slightly
inclined to the primary's equatorial plane, reminiscent of the inner satellites
of other asteroid triple systems. Comparison of the near-infrared spectrum of
the larger satellite reveals no significant difference with Camilla. Hence,
these properties argue for a formation of the satellites by excavation from
impact and re-accumulation of ejecta. We determine the spin and 3-D shape of
Camilla. The model fits well each data set. We determine Camilla to be larger
than reported from modeling of mid-infrared photometry, with a
spherical-volume-equivalent diameter of 254 $\pm$ 36 km (3 $\sigma$
uncertainty), in agreement with recent results from shape modeling
(Hanus2017+). Combining the mass of (1.12 $\pm$ 0.01) $\times$ 10$^{19}$ kg
determined from the dynamics of the satellites and the volume from the 3-D
shape model, we determine a density of 1,280 $\pm$ 130 SI. From this density,
and considering Camilla's spectral similarities with (24) Themis and (65)
Cybele (for which water ice coating on surface grains was reported), we infer a
silicate-to-ice mass ratio of 1-6, with a 10-30% macroporosity. | astro-ph_EP |
Jupiter's Para-H$_2$ Distribution from SOFIA/FORCAST and Voyager/IRIS
17-37 $μ$m Spectroscopy: Spatially resolved maps of Jupiter's far-infrared 17-37 $\mu$m
hydrogen-helium collision-induced spectrum were acquired by the FORCAST
instrument on the Stratospheric Observatory for Infrared Astronomy (SOFIA) in
May 2014. Spectral scans in two grisms covered the broad S(0) and S(1)
absorption lines, in addition to contextual imaging in eight broad-band filters
(5-37 $\mu$m) with spatial resolutions of 2-4". The spectra were inverted to
map the zonal-mean temperature and para-H$_2$ distribution ($f_p$, the fraction
of the para spin isomer with respect to the ortho spin isomer) in Jupiter's
upper troposphere (the 100-700 mbar range). We compared these to a reanalysis
of Voyager-1 and -2 IRIS spectra covering the same spectral range. Para-H$_2$
increases from equator to pole, with low-$f_p$ air at the equator representing
sub-equilibrium conditions (i.e., less para-H$_2$ than expected from thermal
equilibration), and high-$f_p$ air and possible super-equilibrium at higher
latitudes. In particular, we confirm the continued presence of a region of
high-$f_p$ air at high northern latitudes discovered by Voyager/IRIS, and an
asymmetry with generally higher $f_p$ in the north than in the south. We note
that existing collision-induced absorption databases lack opacity from
(H$_2$)$_2$ dimers, leading to under-prediction of the absorption near the S(0)
and S(1) peaks. There appears to be no spatial correlation between para-H$_2$
and tropospheric ammonia, phosphine and cloud opacity derived from Voyager/IRIS
at mid-infrared wavelengths (7-15 $\mu$m). We note, however, that para-H$_2$
tracks the similar latitudinal distribution of aerosols within Jupiter's upper
tropospheric and stratospheric hazes observed in reflected sunlight, suggesting
that catalysis of hydrogen equilibration within the hazes (and not the main
clouds) may govern the equator-to-pole gradient. [Abridged] | astro-ph_EP |
Using Dust Shed from Asteroids as Microsamples to Link Remote
Measurements with Meteorite Classes: Given the compositional diversity of asteroids, and their distribution in
space, it is impossible to consider returning samples from each one to
establish their origin. However, the velocity and molecular composition of
primary minerals, hydrated silicates, and organic materials can be determined
by in situ dust detector instruments. Such instruments could sample the cloud
of micrometer-scale particles shed by asteroids to provide direct links to
known meteorite groups without returning the samples to terrestrial
laboratories. We extend models of the measured lunar dust cloud from LADEE to
show that the abundance of detectable impact-generated microsamples around
asteroids is a function of the parent body radius, heliocentric distance, flyby
distance, and speed. We use monte carlo modeling to show that several tens to
hundreds of particles, if randomly ejected and detected during a flyby, would
be a sufficient number to classify the parent body as an ordinary chondrite,
basaltic achondrite, or other class of meteorite. Encountering and measuring
microsamples shed from near-earth and main-belt asteroids, coupled with
complementary imaging and multispectral measurements, could accomplish a
thorough characterization of small, airless bodies. | astro-ph_EP |
Application of the MEGNO technique to the dynamics of Jovian irregular
satellites: We apply the MEGNO (Mean Exponential Growth of Nearby Orbits) technique to
the dynamics of Jovian irregular satellites. We demonstrate the efficiency of
applying the MEGNO indicator to generate a mapping of relevant phase-space
regions occupied by observed jovian irregular satellites. The construction of
MEGNO maps of the Jovian phase-space region within its Hill-sphere is addressed
and the obtained results are compared with previous studies regarding the
dynamical stability of irregular satellites. Since this is the first time the
MEGNO technique is applied to study the dynamics of irregular satellites we
provide a review of the MEGNO theory. We consider the elliptic restricted
three-body problem in which Jupiter is orbited by a massless test satellite
subject to solar gravitational perturbations. The equations of motion of the
system are integrated numerically and the MEGNO indicator computed from the
systems variational equations. An unprecedented large set of initial conditions
are studied to generate the MEGNO maps. The chaotic nature of initial
conditions are demonstrated by studying a quasi-periodic orbit and a chaotic
orbit. As a result we establish the existence of several high-order mean-motion
resonances detected for retrograde orbits along with other interesting
dynamical features. The computed MEGNO maps allows to qualitatively
differentiate between chaotic and quasi-periodic regions of the irregular
satellite phase-space given only a relatively short integration time. By
comparing with previous published results we can establish a correlation
between chaotic regions and corresponding regions of orbital instability. | astro-ph_EP |
Evidence for H$_{2}$ Dissociation and Recombination Heat Transport in
the Atmosphere of KELT-9b: Phase curve observations provide an opportunity to study the full energy
budgets of exoplanets by quantifying the amount of heat redistributed from
their daysides to their nightsides. Theories explaining the properties of phase
curves for hot Jupiters have focused on the balance between radiation and
dynamics as the primary parameter controlling heat redistribution. However,
recent phase curves have shown deviations from the trends that emerge from this
theory, which has led to work on additional processes that may affect hot
Jupiter energy budgets. One such process, molecular hydrogen dissociation and
recombination, can enhance energy redistribution on ultra-hot Jupiters with
temperatures above $\sim2000$ K. In order to study the impact of H$_{2}$
dissociation on ultra-hot Jupiters, we present a phase curve of KELT-9b
observed with the Spitzer Space Telescope at 4.5 $\mu$m. KELT-9b is the hottest
known transiting planet, with a 4.5-$\mu$m dayside brightness temperature of
$4566^{+140}_{-136}$ K and a nightside temperature of $2556^{+101}_{-97}$ K. We
observe a phase curve amplitude of $0.609 \pm 0.020$ and a hot spot offset of
$18.7^{+2.1}_{-2.3}$ degrees. The observed amplitude is too small to be
explained by a simple balance between radiation and advection. General
circulation models (GCMs) and an energy balance model that include the effects
of H$_{2}$ dissociation and recombination provide a better match to the data.
The GCMs, however, predict a maximum hot spot offset of $5$ degrees, which
disagrees with our observations at $>5\sigma$ confidence. This discrepancy may
be due to magnetic effects in the planet's highly ionized atmosphere. | astro-ph_EP |
Polarimetric and Photometric Observations of NEAs; (422699) 2000 PD3 and
(3200) Phaethon with the 1.6m Pirka Telescope: We report on optical polarimetric observations of two Apollo type near-Earth
asteroids, (422699) 2000 PD3 and (3200) Phaethon, and BVRI photometric
observations of 2000 PD3 using the 1.6m Pirka telescope in 2017. We derived the
geometric albedo of pv = 0.22 +- 0.06 and the color indices (B-V = 0.282 +-
0.072, V-R = 0.198 +- 0.035 and V-I = 0.203 +- 0.022) for 2000 PD3 which are
consistent with those of S-type asteroids (including Q-types). The effective
diameter of 2000 PD3 was derived as 0.69 +- 0.15 km using our derived geometric
albedo. We found that our polarimetric data of Phaethon in 2017 is deviated
from the polarimetric profile taken at different epoch of 2016 using the
identical instrument setting (Ito et al., 2018). This result suggests that
Phaethon would have a regional heterogeneity in grain size and/or albedo on its
surface. | astro-ph_EP |
Orbital evolution under the action of fast interstellar gas flow with
non-constant drag coefficient: The acceleration of a spherical dust particle caused by an interstellar gas
flow depends on the drag coefficient which is, for the given particle and flow
of interstellar gas, a specific function of the relative speed of the dust
particle with respect to the interstellar gas. We investigate the motion of a
dust particle in the case when the acceleration caused by the interstellar gas
flow represent a small perturbation to the gravity of a central star. We
present the secular time derivatives of the Keplerian orbital elements of the
dust particle under the action of the acceleration from the interstellar gas
flow for arbitrary orbit orientation. The semimajor axis of the dust particle
is a decreasing function of time for an interstellar gas flow acceleration with
constant drag coefficient and also for such an acceleration with the linearly
variable drag coefficient. The decrease of the semimajor axis is slower for the
interstellar gas flow acceleration with the variable drag coefficient. The
minimal and maximal values of the decrease of the semimajor axis are
determined. In the planar case, when the interstellar gas flow velocity lies in
the orbital plane of the particle, the orbit always approaches the position
with the maximal value of the transversal component of the interstellar gas
flow velocity vector measured at perihelion.
The properties of the orbital evolution derived from the secular time
derivatives are consistent with numerical integrations of the equation of
motion. If the interstellar gas flow speed is much larger than the speed of the
dust particle, then the linear approximation of dependence of the drag
coefficient on the relative speed of the dust particle with respect to the
interstellar gas is usable for practically arbitrary (no close to zero) values
of the molecular speed ratios (Mach numbers). | astro-ph_EP |
Tilting Uranus via Secular Spin-Orbit Resonance with Planet 9: Uranus' startlingly large obliquity of 98 degrees has yet to admit a
satisfactory explanation. The most widely accepted hypothesis involving a giant
impactor that tipped Uranus onto its side encounters several difficulties with
regards to the Uranus' spin rate and its prograde satellite system. An
obliquity increase that was driven by capture of Uranus into a secular
spin-orbit resonance remains a possible alternative hypothesis that avoids many
of the issues associated with a giant impact. We propose that secular
spin-orbit resonance could have excited Uranus' obliquity to its present day
value if it was driven by the outward migration of an as-yet undetected outer
Solar System body commonly known as Planet Nine. We draw support for our
hypothesis from an analysis of 123 N-body simulations with varying parameters
for Planet Nine and its migration. We find that in multiple instances, a
simulated Planet Nine drives Uranus' obliquity past 98 degrees, with a
significant number falling within 10 percent of this value. We note a
significant caveat to our results in that a much faster than present-day
spin-axis precession rate for Uranus is required in all cases for it to reach
high obliquities. We conclude that while it was in principle possible for
Planet Nine (if it exists) to have been responsible for Uranus' obliquity, the
feasibility of such a result hinges on Uranus' primordial precession rate. | astro-ph_EP |
Prospects for detecting decreasing exoplanet frequency with main
sequence age using PLATO: The space mission PLATO will usher in a new era of exoplanetary science by
expanding our current inventory of transiting systems and constraining host
star ages, which are currently highly uncertain. This capability might allow
PLATO to detect changes in planetary system architecture with time,
particularly because planetary scattering due to Lagrange instability may be
triggered long after the system was formed. Here, we utilize previously
published instability timescale prescriptions to determine PLATO's capability
to detect a trend of decreasing planet frequency with age for systems with
equal-mass planets. For two-planet systems, our results demonstrate that PLATO
may detect a trend for planet masses which are at least as massive as
super-Earths. For systems with three or more planets, we link their initial
compactness to potentially detectable frequency trends in order to aid future
investigations when these populations will be better characterized. | astro-ph_EP |
Higher Martian atmospheric temperatures at all altitudes increase the
D/H fractionation factor and water loss: Much of the water that once flowed on the surface of Mars was lost to space
long ago, and the total amount lost remains unknown. Clues to the amount lost
can be found by studying hydrogen (H) and its isotope deuterium (D), which are
produced when atmospheric water molecules H$_2$O and HDO dissociate. The
difference in escape efficiencies of H and D (which leads to} an enhanced D/H
ratio) is referred to as the fractionation factor $f$. Both the D/H ratio and
$f$ are necessary to estimate water loss; thus, if we can constrain the range
of $f$ and understand what controls it, we will be able to estimate water loss
more accurately. In this study, we use a 1D photochemical model of the neutral
Martian atmosphere to determine how $f$ depends on assumed temperature and
water vapor profiles. We find that the exobase temperature most strongly
controls the value of $f$ for thermal escape processes. When we include
estimates of non-thermal escape from other studies, we find that the tropopause
temperature is also important. Overall, for the standard Martian atmosphere,
$f=0.002$ for thermal escape, and $f=0.06$ for thermal + non-thermal escape. We
estimate that Mars has lost at minimum 66-122 m GEL of water. Importantly, our
results demonstrate that the value of $f$ depends critically on non-thermal
escape of D, and that modeling studies that include D/H fractionation must
model both neutral and ion processes throughout the atmosphere. | astro-ph_EP |
Investigating Thermal Contrasts Between Jupiter's Belts, Zones, and
Polar Vortices with VLT/VISIR: Using images at multiple mid-infrared wavelengths, acquired in May 2018 using
the VISIR instrument on ESO's Very Large Telescope (VLT), we study Jupiter's
pole-to-pole thermal, chemical and aerosol structure in the troposphere and
stratosphere. We confirm that the pattern of cool and cloudy anticyclonic zones
and warm cloud-free cyclonic belts persists throughout the mid-latitudes, up to
the polar boundaries, and evidence a strong correlation with the vertical
maximum windshear and the locations of Jupiter's zonal jets. At high latitudes,
VISIR images reveal a large region of mid-infrared cooling poleward
$\sim$64$^{\circ}$N and $\sim$67$^{\circ}$S extending from the upper
troposphere to the stratosphere, co-located with the reflective aerosols
observed by JunoCam, and suggesting that aerosols play a key role in the
radiative cooling at the poles. Comparison of zonal-mean thermal properties and
high-resolution visible imaging from Juno allows us to study the variability of
atmospheric properties as a function of altitude and jet boundaries,
particularly in the cold southern polar vortex. However, the southern
stratospheric polar vortex is partly masked by a warm mid-infrared signature of
the aurora. Co-located with the southern main auroral oval, this warming
results from the auroral precipitation and/or joule heating which heat the
atmosphere and thus cause a significant stratospheric emission. This high
emission results from a large enhancement of both ethane and acetylene in the
polar region, reinforcing the evidence of enhanced ion-related chemistry in
Jupiter's auroral regions. | astro-ph_EP |
The Direct Detectability of Giant Exoplanets in the Optical: Motivated by the possibility that a coronagraph will be put on WFIRST/AFTA,
we explore the direct detectability of extrasolar giant planets (EGPs) in the
optical. We quantify a planet's detectability by the fraction of its orbit for
which it is in an observable configuration ($f_\mathrm{obs}$). Using a suite of
Monte Carlo experiments, we study the dependence of $f_\mathrm{obs}$ upon the
inner working angle (IWA) and minimum achievable contrast ($C_\mathrm{min}$) of
the direct-imaging observatory; the planet's phase function, geometric albedo,
single-scattering albedo, radius, and distance from Earth; and the semi-major
axis distribution of EGPs. We calculate phase functions for a given geometric
or single-scattering albedo, assuming various scattering mechanisms. We find
that the Lambertian phase function can predict significantly larger
$f_\mathrm{obs}$'s with respect to the more realistic Rayleigh phase function.
For observations made with WFIRST/AFTA's baseline capabilities
($C_\mathrm{min}\sim10^{-9}$, $\mathrm{IWA}\sim0.2''$), Jupiter-like planets
orbiting stars within 10, 30, and 50 parsecs of Earth have volume-averaged
observability fractions of ${\sim}$12%, 3%, and 0.5%, respectively. At 10
parsecs, such observations yield $f_\mathrm{obs}>1\%$ for low- to
modest-eccentricity planets with semi-major axes in the range ${\sim}2 - 10$
AU. If $C_\mathrm{min}=10^{-10}$, this range extends to ${\sim}35$ AU. We find
that, in all but the most optimistic configurations, the probability for
detection in a blind search is low (${<}\,5\%$). However, with orbital
parameter constraints from long-term radial-velocity campaigns and Gaia
astrometry, the tools we develop in this work can be used to determine both the
most promising systems to target and when to observe them. | astro-ph_EP |
Tidal Distortions as a Bottleneck on Constraining Exoplanet Compositions: Improvements in the number of confirmed planets and the precision of
observations imply a need to better understand subtle effects that may bias
interpretations of exoplanet observations. One such effect is the distortion of
a short period planet by its host star, affecting its derived density. We
extend the work of Burton et al., Correia, and others, using a gravitational
potential formulation to a sample of nearly 200 planets with periods less than
3 days. We find five planets exhibiting density variations of >10% and as many
as 20 planets with deviations >5%. We derive an analytic approximation for this
deviation as a function of the orbital period, transit depth, and mass ratio
between the planet and host star, allowing for rapid determination of such
tidal effects. We find that current density error bars are typically larger
than tidal deviations but that reducing the uncertainty on transit depth and
radial velocity (RV) amplitude by a factor of 3 causes tidal effects to
dominate density errors (>50%) in >40% of planets in our sample, implying that
in the near future upgraded observational precision will cause shape deviations
to become a bottleneck with regards to analysis of exoplanet compositions.
These two parameters are found to dominate uncertainties compared to errors on
stellar mass and radius. We identify a group of eight planets (including
WASP-19 b, HAT-P-7 b, and WASP-12 b) for which current density uncertainties
are as much as 4x smaller than the potential shift due to tides, implying a
possible 4{\sigma} bias on their density estimates. | astro-ph_EP |
Space based microlensing planet searches: The discovery of extra-solar planets is arguably the most exciting
development in astrophysics during the past 15 years, rivalled only by the
detection of dark energy. Two projects unite the communities of exoplanet
scientists and cosmologists: the proposed ESA M class mission EUCLID and the
large space mission WFIRST, top ranked by the Astronomy 2010 Decadal Survey
report. The later states that: "Space-based microlensing is the optimal
approach to providing a true statistical census of planetary systems in the
Galaxy, over a range of likely semi-major axes". They also add: "This census,
combined with that made by the Kepler mission, will determine how common
Earth-like planets are over a wide range of orbital parameters". We will
present a status report of the results obtained by microlensing on exoplanets
and the new objectives of the next generation of ground based wide field imager
networks. We will finally discuss the fantastic prospect offered by space based
microlensing at the horizon 2020-2025. | astro-ph_EP |
Comparison of different exoplanet mass detection limit methods using a
sample of main-sequence intermediate-type stars: The radial velocity (RV) technique is a powerful tool for detecting
extrasolar planets and deriving mass detection limits that are useful for
constraining planet pulsations and formation models. Detection limit methods
must take into account the temporal distribution of power of various origins in
the stellar signal. These methods must also be able to be applied to large
samples of stellar RV time series We describe new methods for providing
detection limits. We compute the detection limits for a sample of ten main
sequence stars, which are of G-F-A type, in general active, and/or with
detected planets, and various properties. We use them to compare the
performances of these methods with those of two other methods used in the
litterature. We obtained detection limits in the 2-1000 day period range for
ten stars. Two of the proposed methods, based on the correlation between
periodograms and the power in the periodogram of the RV time series in specific
period ranges, are robust and represent a significant improvement compared to a
method based on the root mean square of the RV signal. We conclude that two of
the new methods (correlation-based method and local power analysis, i.e. LPA,
method) provide robust detection limits, which are better than those provided
by methods that do not take into account the temporal sampling. | astro-ph_EP |
Equilibrium Configurations of Synchronous Binaries: Numerical Solutions
and Application to Kuiper-Belt Binary 2001 QG298: We present numerical computations of the equilibrium configurations of
tidally-locked homogeneous binaries, rotating in circular orbits. Unlike the
classical Roche approximations, we self-consistently account for the tidal and
rotational deformations of both components, and relax the assumptions of
ellipsoidal configurations and Keplerian rotation. We find numerical solutions
for mass ratios q between 1e-3 and 1, starting at a small angular velocity for
which tidal and rotational deformations are small, and following a sequence of
increasing angular velocities. Each series terminates at an appropriate ``Roche
limit'', above which no equilibrium solution can be found. Even though the
Roche limit is crossed before the ``Roche lobe'' is filled, any further
increase in the angular velocity will result in mass-loss. For close,
comparable-mass binaries, we find that local deviations from ellipsoidal forms
may be as large as 10-20%, and departures from Keplerian rotation are
significant. We compute the light curves that arise from our equilibrium
configurations, assuming their distance is >>1 AU (e.g. in the Kuiper Belt). We
consider both backscatter (proportional to the projected area) and diffuse
(Lambert) reflections. Backscatter reflection always yields two minima of equal
depths. Diffuse reflection, which is sensitive to the surface curvature,
generally gives rise to unequal minima. We find detectable intensity
differences of up to 10% between our light curves and those arising from the
Roche approximations. Finally, we apply our models to Kuiper Belt binary 2001
QG298, and find a nearly edge-on binary with a mass ratio q = 0.93
^{+0.07}_{-0.03}, angular velocity Omega^2/G rho = 0.333+/-0.001 (statistical
errors only), and pure diffuse reflection. For the observed period of 2001
QG298, these parameters imply a bulk density, rho = 0.72 +/- 0.04 g cm^-3. | astro-ph_EP |
Origin of craters on Phoebe: comparison with Cassini's data: Phoebe is one of the irregular satellites of Saturn; the images taken by
Cassini-Huygens spacecraft allowed us to analyze its surface and the craters on
it. We study the craters on Phoebe produced by Centaur objects from the
Scattered Disk (SD) and plutinos escaped from the 3:2 mean motion resonance
with Neptune and compare our results with the observations by Cassini. We use
previous simulations on trans-Neptunian Objects and a method that allows us to
obtain the number of craters and the cratering rate on Phoebe. We obtain the
number of craters and the greatest crater on Phoebe produced by Centaurs in the
present configuration of the Solar System. Moreover, we obtain a present
normalized rate of encounters of Centaurs with Saturn of $\dot F = 7.1 \times
10^{-11}$ per year, from which we can infer the current cratering rate on
Phoebe for each crater diameter. Our study and the comparison with the
observations suggest that the main crater features on Phoebe are unlikely to
have been produced in the present configuration of the Solar System and that
they must have been acquired when the SD were depleted in the early Solar
System. If this is what happened and the craters were produced when Phoebe was
a satellite of Saturn, then it had to be captured, very early in the evolution
of the Solar System. | astro-ph_EP |
Probing the Protosolar Disk Using Dust Filtering at Gaps in the Early
Solar System: Jupiter and Saturn formed early, before the gas disk dispersed. The presence
of gap-opening planets affects the dynamics of the gas and embedded solids and
halts the inward drift of grains above a certain size. A drift barrier can
explain the absence of calcium aluminium rich inclusions (CAIs) in chondrites
originating from parent bodies that accreted in the inner solar system.
Employing an interdisciplinary approach, we use a $\mu$-X-Ray-fluorescence
scanner to search for large CAIs and a scanning electron microscope to search
for small CAIs in the ordinary chondrite NWA 5697. We carry out long-term,
two-dimensional simulations including gas, dust, and planets to characterize
the transport of grains within the viscous $\alpha$-disk framework exploring
the scenarios of a stand-alone Jupiter, Jupiter and Saturn \textit{in situ}, or
Jupiter and Saturn in a 3:2 resonance. In each case, we find a critical grain
size above which drift is halted as a function of the physical conditions in
the disk. From the laboratory search we find four CAIs with a largest size of
$\approx$200$\,\mu$m. \Combining models and data, we provide an estimate for
the upper limit of the $\alpha$-viscosity and the surface density at the
location of Jupiter, using reasonable assumptions about the stellar accretion
rate during inward transport of CAIs, and assuming angular momentum transport
to happen exclusively through viscous effects. Moreover, we find that the
compound gap structure in the presence of Saturn in a 3:2 resonance favors
inward transport of grains larger than CAIs currently detected in ordinary
chondrites. | astro-ph_EP |
Giant planets around two intermediate-mass evolved stars and
confirmation of the planetary nature of HIP67851 c: Precision radial velocities are required to discover and characterize planets
orbiting nearby stars. Optical and near infrared spectra that exhibit many
hundreds of absorption lines can allow the m/s precision levels required for
such work. However, this means that studies have generally focused on
solar-type dwarf stars. After the main-sequence, intermediate-mass stars
(former A-F stars) expand and rotate slower than their progenitors, thus
thousands of narrow absorption lines appear in the optical region, permitting
the search for planetary Doppler signals in the data for these types of stars.
We present the discovery of two giant planets around the intermediate-mass
evolved star HIP65891 and HIP107773. The best Keplerian fit to the HIP65891 and
HIP107773 radial velocities leads to the following orbital parameters: P=1084.5
d; m$_b$sin$i$ = 6.0 M$_{jup}$; $e$=0.13 and P=144.3 d; m$_b$sin$i$ = 2.0
M$_{jup}$; $e$=0.09, respectively. In addition, we confirm the planetary nature
of the outer object orbiting the giant star HIP67851. The orbital parameters of
HIP67851c are: P=2131.8 d, m$_c$sin$i$ = 6.0 M$_{jup}$ and $e$=0.17. With
masses of 2.5 M$_\odot$ and 2.4 M$_\odot$ HIP65891 and HIP107773 are two of the
most massive stars known to host planets. Additionally, HIP67851 is one of five
giant stars that are known to host a planetary system having a close-in planet
($a <$ 0.7 AU). Based on the evolutionary states of those five stars, we
conclude that close-in planets do exist in multiple systems around subgiants
and slightly evolved giants stars, but probably they are subsequently destroyed
by the stellar envelope during the ascent of the red giant branch phase. As a
consequence, planetary systems with close-in objects are not found around
horizontal branch stars. | astro-ph_EP |
A JWST NIRSpec Phase Curve for WASP-121b: Dayside Emission Strongest
Eastward of the Substellar Point and Nightside Conditions Conducive to Cloud
Formation: We present the first exoplanet phase curve measurement made with the JWST
NIRSpec instrument, highlighting the exceptional stability of this
newly-commissioned observatory for exoplanet climate studies. The target,
WASP-121b, is an ultrahot Jupiter with an orbital period of 30.6 hr. We analyze
two broadband light curves generated for the NRS1 and NRS2 detectors, covering
wavelength ranges of 2.70-3.72 micron and 3.82-5.15 micron, respectively. Both
light curves exhibit minimal systematics, with approximately linear drifts in
the baseline flux level of 30 ppm/hr (NRS1) and 10 ppm/hr (NRS2). Assuming a
simple brightness map for the planet described by a low-order spherical
harmonic dipole, our light curve fits suggest that the phase curve peaks
coincide with orbital phases $3.36 \pm 0.11$ deg (NRS1) and $2.66 \pm 0.12$ deg
(NRS2) prior to mid-eclipse. This is consistent with the strongest dayside
emission emanating from eastward of the substellar point. We measure
planet-to-star emission ratios of $3,924 \pm 7$ ppm (NRS1) and $4,924 \pm 9$
ppm (NRS2) for the dayside hemisphere, and $136 \pm 8$ ppm (NRS1) and $630 \pm
10$ ppm (NRS2) for the nightside hemisphere. The latter nightside emission
ratios translate to planetary brightness temperatures of $926 \pm 12$ K (NRS1)
and $1,122 \pm 10$ K (NRS2), which are low enough for a wide range of
refractory condensates to form, including enstatite and forsterite. A nightside
cloud deck may be blocking emission from deeper, hotter layers of the
atmosphere, potentially helping to explain why cloud-free 3D general
circulation model simulations systematically over-predict the nightside
emission for WASP-121b. | astro-ph_EP |
Phosphine on Venus Cannot be Explained by Conventional Processes: The recent candidate detection of ~1 ppb of phosphine in the middle
atmosphere of Venus is so unexpected that it requires an exhaustive search for
explanations of its origin. Phosphorus-containing species have not been
modelled for Venus' atmosphere before and our work represents the first attempt
to model phosphorus species in the Venusian atmosphere. We thoroughly explore
the potential pathways of formation of phosphine in a Venusian environment,
including in the planet's atmosphere, cloud and haze layers, surface, and
subsurface. We investigate gas reactions, geochemical reactions,
photochemistry, and other non-equilibrium processes. None of these potential
phosphine production pathways are sufficient to explain the presence of ppb
phosphine levels on Venus. If PH3's presence in Venus' atmosphere is confirmed,
it therefore is highly likely to be the result of a process not previously
considered plausible for Venusian conditions. The process could be unknown
geochemistry, photochemistry, or even aerial microbial life, given that on
Earth phosphine is exclusively associated with anthropogenic and biological
sources. The detection of phosphine adds to the complexity of chemical
processes in the Venusian environment and motivates in situ follow up sampling
missions to Venus. Our analysis provides a template for investigation of
phosphine as a biosignature on other worlds. | astro-ph_EP |
HATS-19b, HATS-20b, HATS-21b: Three Transiting Hot-Saturns Discovered by
the HATSouth Survey: We report the discovery by the HATSouth exoplanet survey of three hot-Saturn
transiting exoplanets: HATS-19b, HATS-20b, and HATS-21b. The planet host
HATS-19 is a slightly evolved V = 13.0 G0 star with [Fe/H] = 0.240, a mass of
1.303 Msun, and a radius of 1.75 Rsun. HATS-19b is in an eccentric orbit (e =
0.30) around this star with an orbital period of 4.5697 days and has a mass of
0.427 Mjup and a highly inflated radius of 1.66 Rjup. The planet HATS-20b has a
Saturn-like mass and radius of 0.273 Mjup and 0.776 Rjup respectively. It
orbits the V = 13.8 G9V star HATS-20 (Ms = 0.910 Msun; Rs = 0.892 Rsun) with a
period of 3.7993 days. Finally, HATS-21 is a V = 12.2 G4V star with [Fe/H] =
0.300, a mass of 1.080 Msun, and a radius of 1.021 Rsun. Its accompanying
planet HATS-21b has a 3.5544-day orbital period, a mass of 0.332 Mjup, and a
moderately inflated radius of 1.123 Rjup. With the addition of these three very
different planets to the growing sample of hot-Saturns, we re-examine the
relations between the observed giant planet radii, stellar irradiation, and
host metallicity. We find a significant positive correlation between planet
equilibrium temperature and radius, and a weak negative correlation between
host metallicity and radius. To assess the relative influence of various
physical parameters on observed planet radii, we train and fit models using
Random Forest regression. We find that for hot-Saturns (0.1 < Mp < 0.5 Mjup),
the planetary mass and equilibrium temperature play dominant roles in
determining radii. For hot-Jupiters (0.5 < Mp < 2.0 Mjup), the most important
parameter is equilibrium temperature alone. Finally, for irradiated higher-mass
planets (Mp > 2.0 Mjup), we find that equilibrium temperature dominates in
influence, with smaller contributions from planet mass and host metallicity. | astro-ph_EP |
Light Curve Analysis of Ground-Based Data from Exoplanets Transit
Database: Photometric observations of exoplanet transits can be used to derive the
orbital and physical parameters of an exoplanet. We analyzed several transit
light curves of exoplanets that are suitable for ground-based observations
whose complete information is available on the Exoplanet Transit Database
(ETD). We analyzed transit data of planets including HAT-P-8 b, HAT-P-16 b,
HAT-P-21 b, HAT-P-22 b, HAT-P-28 b and HAT-P-30 b using the AstroImageJ (AIJ)
software package. In this paper, we investigated 82 transit light curves from
ETD, deriving their physical parameters as well as computing their mid-transit
times for future Transit Timing Variation (TTV) analyses. The Precise values of
the parameters show that using AIJ as a fitting tool for follow-up observations
can lead to results comparable to the values at the NASA Exoplanet Archive (the
NEA). Such information will be invaluable considering the numbers of future
discoveries from the ground and space-based exoplanet surveys. | astro-ph_EP |
GJ 1252b: A Hot Terrestrial Super-Earth With No Atmosphere: The increasing numbers of rocky, terrestrial exoplanets known to orbit nearby
stars (especially M dwarfs) has drawn increased attention to the possibility of
studying these planets' surface properties, and atmospheric compositions &
escape histories. Here we report the detection of the secondary eclipse of the
terrestrial exoplanet GJ1252b using the Spitzer Space Telescope's IRAC2 4.5
micron channel. We measure an eclipse depth of 149(+25/-32) ppm, corresponding
to a day-side brightness temperature of 1410(+91/-125) K and consistent with
the prediction for no atmosphere. Comparing our measurement to atmospheric
models indicates that GJ1252b has a surface pressure of <10 bar, substantially
less than Venus. Assuming energy-limited escape, even a 100 bar atmosphere
would be lost in <1 Myr, far shorter than estimated age of 3.9+/-0.4 Gyr. The
expected mass loss could be overcome by mantle outgassing, but only if the
mantle's carbon content were >7% by mass - over two orders of magnitude greater
than that found in Earth. We therefore conclude that GJ1252b has no significant
atmosphere. Model spectra with granitoid or feldspathic surface composition,
but with no atmosphere, are disfavored at >2 sigma. The eclipse occurs just
+1.4(+2.8/-1.0) min after orbital phase 0.5, indicating e cos
omega=+0.0025(+0.0049/-0.0018), consistent with a circular orbit. Tidal heating
is therefore likely to be negligible to GJ1252b's global energy budget.
Finally, we also analyze additional, unpublished TESS transit photometry of
GJ1252b which improves the precision of the transit ephemeris by a factor of
ten, provides a more precise planetary radius of 1.180+/-0.078 R_E, and rules
out any transit timing variations with amplitudes <1 min. | astro-ph_EP |
The role of planetary formation and evolution in shaping the composition
of exoplanetary atmospheres: Over the last twenty years, the search for extrasolar planets revealed us the
rich diversity of the outcomes of the formation and evolution of planetary
systems. In order to fully understand how these extrasolar planets came to be,
however, the orbital and physical data we possess are not enough, and they need
to be complemented with information on the composition of the exoplanets.
Ground-based and space-based observations provided the first data on the
atmospheric composition of a few extrasolar planets, but a larger and more
detailed sample is required before we can fully take advantage of it. The
primary goal of the Exoplanet Characterization Observatory (EChO) is to fill
this gap, expanding the limited data we possess by performing a systematic
survey of hundreds of extrasolar planets. The full exploitation of the data
that EChO and other space-based and ground-based facilities will provide in the
near future, however, requires the knowledge of what are the sources and sinks
of the chemical species and molecules that will be observed. Luckily, the study
of the past history of the Solar System provides several indications on the
effects of processes like migration, late accretion and secular impacts, and on
the time they occur in the life of planetary systems. In this work we will
review what is already known about the factors influencing the composition of
planetary atmospheres, focusing on the case of gaseous giant planets, and what
instead still need to be investigated. | astro-ph_EP |
Planetesimal fragmentation and giant planet formation: the role of
planet migration: In the standard model of core accretion, the cores of the giant planets form
by the accretion of planetesimals. In this scenario, the evolution of the
planetesimal population plays an important role in the formation of massive
cores. Recently, we studied the role of planetesimal fragmentation in the in
situ formation of a giant planet. However, the exchange of angular momentum
between the planet and the gaseous disk causes the migration of the planet in
the disk. In this new work, we incorporate the migration of the planet and
globally study the role of planet migration in the formation of a massive core
when the population of planetesimals evolves by planet accretion, migration due
to the nebular drag, and fragmentation due to planetesimal collisions. | astro-ph_EP |
OSSOS: IV. Discovery of a dwarf planet candidate in the 9:2 resonance
with Neptune: We report the discovery and orbit of a new dwarf planet candidate, 2015
RR$_{245}$, by the Outer Solar System Origins Survey (OSSOS). 2015 RR$_{245}$'s
orbit is eccentric ($e=0.586$), with a semi-major axis near 82 au, yielding a
perihelion distance of 34 au. 2015 RR$_{245}$ has $g-r = 0.59 \pm 0.11$ and
absolute magnitude $H_{r} = 3.6 \pm 0.1$; for an assumed albedo of $p_V = 12$%
the object has a diameter of $\sim670$ km. Based on astrometric measurements
from OSSOS and Pan-STARRS1, we find that 2015 RR$_{245}$ is securely trapped on
ten-Myr timescales in the 9:2 mean-motion resonance with Neptune. It is the
first TNO identified in this resonance. On hundred-Myr timescales, particles in
2015 RR$_{245}$-like orbits depart and sometimes return to the resonance,
indicating that 2015 RR$_{245}$ likely forms part of the long-lived metastable
population of distant TNOs that drift between resonance sticking and actively
scattering via gravitational encounters with Neptune. The discovery of a 9:2
TNO stresses the role of resonances in the long-term evolution of objects in
the scattering disk, and reinforces the view that distant resonances are
heavily populated in the current Solar System. This object further motivates
detailed modelling of the transient sticking population. | astro-ph_EP |
A New Desalination Pump Help Define the pH of Ocean Worlds: We study ocean exoplanets, for which the global surface ocean is separated
from the rocky interior by a high-pressure ice mantle. We describe a mechanism
that can pump salts out of the ocean, resulting in oceans of very low salinity.
Here we focus on the H2O-NaCl system, though we discuss the application of this
pump to other salts as well. We find our ocean worlds to be acidic, with a pH
in the range of 2-4. We discuss and compare between the conditions found within
our studied oceans and the conditions in which polyextremophiles were
discovered. This work focuses on exoplanets in the super-Earth mass range (2
M_Earth), with water composing at least a few percent of their mass. Although,
the principal of the desalination pump may extend beyond this mass range. | astro-ph_EP |
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