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A new analysis of the GJ581 extrasolar planetary system: We have done a new analysis of the available observations for the GJ581
exoplanetary system. Today this system is controversial due to choices that can
be done in the orbital determination. The main ones are the ocurrence of
aliases and the additional bodies - the planets f and g - announced in Vogt et
al. 2010. Any dynamical study of exoplanets requires the good knowledge of the
orbital elements and the investigations involving the planet g are particularly
interesting, since this body would lie in the Habitable Zone (HZ) of the star
GJ581. This region,for this system, is very attractive of the dynamical point
of view due to several resonances of two and three bodies present there. In
this work, we investigate the conditions under which the planet g may exist. We
stress the fact that the planet g is intimately related with the orbital
elements of the planet d; more precisely, we conclude that it is not possible
to disconnect its existence from the determination of the eccentricity of the
planet d. Concerning the planet f, we have found one solution with period
$\approx 450$ days, but we are judicious about any affirmation concernig this
body because its signal is in the threshold of detection and the high period is
in a spectral region where the ocorruence of aliases is very common. Besides,
we outline some dynamical features of the habitable zone with the dynamical map
and point out the role played by some resonances laying there. | astro-ph_EP |
Null transit detections of 68 radial velocity exoplanets observed by
TESS: In recent years the number of exoplanets has grown considerably. The most
successful techniques in these detections are the radial velocity (RV) and
planetary transits techniques, the latter significantly advanced by the Kepler,
K2 and, more recently, the TESS missions. The detection of exoplanets both by
means of transit and by RVs is of importance, because this would allows
characterizing their bulk densities, and internal compositions. The Transiting
Exoplanet Survey Satellite (TESS) survey offers a unique possibility to search
for transits of extrasolar planets detected by RV. In this work, we present the
results of the search for transits of planets detected with the radial velocity
technique, using the photometry of the TESS space mission. We focus on systems
with super-Earths and Neptunes planets on orbits with periods shorter than 30
days. This cut is intended to keep objects with a relatively high transit
probability, and is also consistent with duration of TESS observations on a
single sector. Given the summed geometric transit probabilities, the expected
number of transiting planets is $3.4 \pm 1.8$. The sample contains two known
transiting planets. We report null results for the remaining 66 out of 68
planets studied, and we exclude in all cases planets larger than 2.4
R$_{\oplus}$, under the assumption of central transits. The remaining two
planets orbit HD~136352 and have been recently been announced. | astro-ph_EP |
Reflected spectroscopy of small exoplanets III: probing the UV band to
measure biosignature gasses: Direct-imaging observations of terrestrial exoplanets will enable their
atmospheric characterization and habitability assessment. Considering the
Earth, the key atmospheric signatures for the biosphere is O$_2$ and the
photochemical product O$_3$. However, this O$_2$-O$_3$ biosignature is not
detectable in the visible wavelengths for most of the time after the emergence
of oxygenic photosynthesis life (i.e., the Proterozoic Earth). Here we
demonstrate spectroscopic observations in the ultraviolet wavelengths for
detecting and characterizing O$_2$ and O$_3$ in Proterozoic Earth-like planets,
using ExoReL$^\Re$. For an O$_2$ mixing ratio 2 to 3 orders of magnitude less
than the present-day Earth, and an O$_3$ mixing ratio of $10^{-7}-10^{-6}$, we
find that O$_3$ can be detected and its mixing ratio can be measured precisely
(within $~1$ order of magnitude) in the ultraviolet ($0.25-0.4\ \mu$m) in
addition to visible-wavelength spectroscopy. With modest spectral resolution
($R=7$) and S/N ($\sim10$) in the ultraviolet, the O$_3$ detection is robust
against other potential gases absorbing in the ultraviolet (e.g., H$_2$S and
SO$_2$), as well as the short-wavelength cutoff between 0.2 and 0.25 $\mu$m.
While the O$_3$ detection does not rely on the near-infrared spectra, extending
the wavelength coverage to the near-infrared ($1-1.8\ \mu$m) would provide
essential information to interpret the O$_3$ biosignature, including the mixing
ratio of H$_2$O, the cloud pressure, as well as the determination of the
dominant gas of the atmosphere. The ultraviolet and near-infrared capabilities
should thus be evaluated as critical components for future missions aiming at
imaging and characterizing terrestrial exoplanets, such as the Habitable Worlds
Observatory. | astro-ph_EP |
Isotope velocimetry: Experimental and theoretical demonstration of the
potential importance of gas flow for isotope fractionation during evaporation
of protoplanetary material: We use new experiments and a theoretical analysis of the results to show that
the isotopic fractionation associated with laser-heating aerodynamic levitation
experiments is consistent with the velocity of flowing gas as the primary
control on the fractionation. The new Fe and Mg isotope data are well explained
where the gas is treated as a low-viscosity fluid that flows around the molten
spheres with high Reynolds numbers and minimal drag. A relationship between the
ratio of headwind velocity to thermal velocity and saturation is obtained on
the basis of this analysis. The recognition that it is the ratio of flow
velocity to thermal velocity that controls fractionation allows for
extrapolation to other environments in which molten rock encounters gas with
appreciable headwinds. In this way, in some circumstances, the degree of
isotope fractionation attending evaporation is as much a velocimeter as it is a
barometer. | astro-ph_EP |
CRISM south polar mapping: First Mars year of observations: We report on mapping of the south polar region of Mars using data from the
Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instrument. Our
observations have led to the following discoveries: 1. Water ice is present in
the form of pole-circling clouds originating from the circum-Hellas region,
beginning prior to Ls=162 and diminishing markedly at Ls=200-204. 2. It has
previously been inferred by temperature measurements(Titus et al., 2003) and
CO2-H2O mixture spectral models (Langevin et al., 2007) that surface water ice
was present in the Cryptic Region in the final stages of sublimation. The high
resolution of CRISM has revealed regions where only water ice is present (not a
CO2-H2O ice mixture). This water ice disappears completely by Ls=252 and may be
the source of water vapor observed by CRISM in southern latitudes between
Ls=240-260 (Smith, et al., this issue). 3. We have estimated surface CO2 ice
grain size distributions for the South Pole Residual Cap (SPRC) and the
seasonal CO2 ice cap that covers it throughout summer spring and summer. Our
analysis suggests that grain sizes peak at Ls=191-199 with an apparent grain
size of ~7 +/-1 cm. By the end of the summer period our analysis demonstrates
minimum apparent grain sizes of ~5 +/-1 mm predominate in the SPRC. 4. Fine
grained CO2 ice condenses from Ls=0-40, and extends symmetrically away from the
geographic pole, extending beyond 80 deg S by Ls=4-10. No evidence for unusual
CO2 depositional processes in the Cryptic Region is observed up to Ls=16. | astro-ph_EP |
Nano dust impacts on spacecraft and boom antenna charging: High rate sampling detectors measuring the potential difference between the
main body and boom antennas of interplanetary spacecraft have been shown to be
efficient means to measure the voltage pulses induced by nano dust impacts on
the spacecraft body itself (see Meyer-Vernet et al, Solar Phys. 256, 463
(2009)). However, rough estimates of the free charge liberated in post impact
expanding plasma cloud indicate that the cloud's own internal electrostatic
field is too weak to account for measured pulses as the ones from the TDS
instrument on the STEREO spacecraft frequently exceeding 0.1 V/m. In this paper
we argue that the detected pulses are not a direct measure of the potential
structure of the plasma cloud, but are rather the consequence of a transitional
interruption of the photoelectron return current towards the portion of the
antenna located within the expanding cloud. | astro-ph_EP |
Long term evolution of planetary systems with a terrestrial planet and a
giant planet: We study the long term orbital evolution of a terrestrial planet under the
gravitational perturbations of a giant planet. In particular, we are interested
in situations where the two planets are in the same plane and are relatively
close. We examine both possible configurations: the giant planet orbit being
either outside or inside the orbit of the smaller planet. The perturbing
potential is expanded to high orders and an analytical solution of the
terrestrial planetary orbit is derived. The analytical estimates are then
compared against results from the numerical integration of the full equations
of motion and we find that the analytical solution works reasonably well. An
interesting finding is that the new analytical estimates improve greatly the
predictions for the timescales of the orbital evolution of the terrestrial
planet compared to an octupole order expansion. Finally, we briefly discuss
possible applications of the analytical estimates in astrophysical problems. | astro-ph_EP |
Fuzzy Characterization of Near-Earth-Asteroids: Due to close encounters with the inner planets, Near-Earth-Asteroids (NEAs)
can have very chaotic orbits. Because of this chaoticity, a statistical
treatment of the dynamical properties of NEAs becomes difficult or even
impossible. We propose a new way to classify NEAs by using methods from Fuzzy
Logic. We demonstrate how a fuzzy characterization of NEAs can be obtained and
how a subsequent analysis can deliver valid and quantitative results concerning
the long-term dynamics of NEAs. | astro-ph_EP |
Observability of Debris Discs around M-stars: Debris discs are second generation dusty discs formed by collisions of
planetesimals. Many debris discs have been found and resolved around hot and
solar-type stars. However, only a handful have been discovered around M-stars,
and the reasons for their paucity remain unclear. Here we check whether the
sensitivity and wavelength coverage of present-day telescopes are simply
unfavourable for detection of these discs or if they are truly rare. We
approach this question by looking at the Herschel/DEBRIS survey that has
searched for debris discs including M-type stars. Assuming that these cool-star
discs are "similar" to those of the hotter stars in some sense (i.e., in terms
of dust location, temperature, fractional luminosity, or mass), we check
whether this survey should have found them. With our procedure we can reproduce
the $2.1^{+4.5}_{-1.7}$% detection rate of M-star debris discs of the DEBRIS
survey, which implies that these discs can indeed be similar to discs around
hotter stars and just avoid detection. We then apply this procedure to IRAM
NIKA-2 and ALMA bands 3, 6 and 7 to predict possible detection rates and give
recommendations for future observations. We do not favour observing with IRAM,
since it leads to detection rates lower than for the DEBRIS survey, with
0.6%-4.5% for a 15 min observation. ALMA observations, with detection rates
0.9%-7.2%, do not offer a significant improvement either, and so we conclude
that more sensitive far-infrared and single dish sub-millimetre telescopes are
necessary to discover the missing population of M-star debris discs. | astro-ph_EP |
Super stellar abundances of alkali metals suggest significant migration
for Hot Jupiters: We investigate the origin of the measured over-abundance of alkali metals in
the atmospheres of hot gas giants, relative to both their host stars and their
atmospheric water abundances. We show that formation exterior to the water snow
line followed by inward disc-driven migration results in excess accretion of
oxygen-poor, refractory-rich material from within the snow-line. This naturally
leads to enrichment of alkali metals in the planetary atmosphere relative to
the bulk composition of its host star but relative abundances of water that are
similar to the stellar host. These relative abundances cannot be explained by
in situ formation which places the refractory elements in the planetary deep
interior rather than the atmosphere. We therefore suggest that the measured
compositions of the atmospheres of hot Jupiters are consistent with significant
migration for at least a subset of hot gas giants. Our model makes robust
predictions about atmospheric composition that can be confirmed with future
data from JWST and Ariel. | astro-ph_EP |
Polarimetric Study of Near-Earth Asteroid (1566) Icarus: We conducted a polarimetric observation of the fast-rotating near-Earth
asteroid (1566) Icarus at large phase (Sun-asteroid-observer's) angles
$\alpha$= 57 deg--141deg around the 2015 summer solstice. We found that the
maximum values of the linear polarization degree are
$P_\mathrm{max}$=7.32$\pm$0.25 % at phase angles of
$\alpha_\mathrm{max}$=124$\pm$8 deg in the $V$-band and
$P_\mathrm{max}$=7.04$\pm$0.21 % at $\alpha_\mathrm{max}$=124$\pm$6 deg in the
$R_\mathrm{C}$-band. Applying the polarimetric slope-albedo empirical law, we
derived a geometric albedo of $p_\mathrm{V}$=0.25$\pm$0.02, which is in
agreement with that of Q-type taxonomic asteroids. $\alpha_\mathrm{max}$ is
unambiguously larger than that of Mercury, the Moon, and another near-Earth
S-type asteroid (4179) Toutatis but consistent with laboratory samples with
hundreds of microns in size. The combination of the maximum polarization degree
and the geometric albedo is in accordance with terrestrial rocks with a
diameter of several hundreds of micrometers. The photometric function indicates
a large macroscopic roughness. We hypothesize that the unique environment
(i.e., the small perihelion distance $q$=0.187 au and a short rotational period
of $T_\mathrm{rot}$=2.27 hours) may be attributed to the paucity of small
grains on the surface, as indicated on (3200) Phaethon. | astro-ph_EP |
A Fireball and Potentially Hazardous Binary Near-Earth Asteroid (164121)
2003 YT$_1$: We present a fireball detected in the night sky over Kyoto, Japan on UT 2017
April 28 at ${\rm 15^{h}\,58^{m}\,19^{s}}$ by the SonotaCo Network. The
absolute visual magnitude is $M_{\rm v}$=$-$4.10$\pm$0.42mag. Luminous light
curves obtain a meteoroid mass $m$=29$\pm$1g, corresponding to the size $a_{\rm
s}$=2.7$\pm$0.1cm. Orbital similarity assessed by D-criterions (cf. $D_{\rm
SH}$=0.0079) has identified a likely parent, the binary near-Earth asteroid
(164121) 2003 YT$_1$. The suggested binary formation process is a YORP-driven
rotational disintegration (Pravec & Harris 2007). The asynchronous state
indicates the age of $<$10$^4$yr, near or shorter than the upper limit to
meteoroid stream lifetime. We examine potential dust production mechanisms for
the asteroid, including rotational instability, resurfacing, impact,
photoionization, radiation pressure sweeping, thermal fracture and sublimation
of ice. We find some of them capable of producing the meteoroid-scale
particles. Rotational instability is presumed to cause mass shedding, in
consideration of the recent precedents (e.g. asteroid (6478) Gault), possibly
releasing mm-cm scale dust particles. Impacts by micrometeorites with size
$\simeq$1mm could be a trigger for ejecting the cm-sized particles. Radiation
pressure can sweep out the mm-sized dust particles, while not sufficient for
the cm-sized. For the other mechanisms, unprovable or unidentified. The
feasibility in the parental aspect of 2003 YT$_1$ is somewhat reconciled with
the fireball observation, yielding an insight into how we approach potentially
hazardous objects. | astro-ph_EP |
A 4565 Myr old andesite from an extinct chondritic protoplanet: The age of iron meteorites implies that accretion of protoplanets began
during the first millions of years of the solar system. Due to the heat
generated by 26Al decay, many early protoplanets were fully differentiated with
an igneous crust produced during the cooling of a magma ocean and the
segregation at depth of a metallic core. The formation and nature of the
primordial crust generated during the early stages of melting is poorly
understood, due in part to the scarcity of available samples. The newly
discovered meteorite Erg Chech 002 (EC 002) originates from one such primitive
igneous crust and has an andesite bulk composition. It derives from the partial
melting of a noncarbonaceous chondritic reservoir, with no depletion in alkalis
relative to the Sun photosphere and at a high degree of melting of around 25
percents. Moreover, EC 002 is, to date, the oldest known piece of an igneous
crust with a 26Al-26Mg crystallization age of 4,565.0 million years (My).
Partial melting took place at 1,220 C up to several hundred kyr before,
implying an accretion of the EC 002 parent body ca. 4,566 My ago. Protoplanets
covered by andesitic crusts were probably frequent. However, no asteroid shares
the spectral features of EC 002, indicating that almost all of these bodies
have disappeared, either because they went on to form the building blocks of
larger bodies or planets or were simply destroyed. | astro-ph_EP |
Synchronous Satellites of Venus: Synchronous satellites of Venus have long been thought unstable, but we use
Poincare's surface of section technique to show that synchronous
quasi-satellites orbiting just outside Venus' Hill sphere are quite stable, at
least for centuries. Such synchrosats always remain within a few degrees of
Venus' equator, and drift very slowly in longitude. These synchrosats could be
useful for continuous monitoring of points on Venus' surface, such as active
landforms or long-lived landers. | astro-ph_EP |
Atomic iron and nickel in the coma of C/1996 B2 (Hyakutake): production
rates, emission mechanisms, and possible parents: Two papers recently reported the detection of gaseous nickel and iron in the
comae of over 20 comets from observations collected over two decades, including
interstellar comet 2I/Borisov. To evaluate the state of the laboratory data in
support of these identifications, we re-analyzed archived spectra of comet
C/1996 B2 (Hyakutake), one of the nearest and brightest comets of the last
century, using a combined experimental and computational approach. We developed
a new, many-level fluorescence model that indicates that the fluorescence
emission of Fe I and Ni I vary greatly with heliocentric velocity. Combining
this model with laboratory spectra of an Fe-Ni plasma, we identified 22 lines
of Fe I and 14 lines of Ni I in the spectrum of Hyakutake. Using Haser models,
we estimate the nickel and iron production rates as Q(Ni) = 2.6 - 4.1 x 10^22
s^-1 and Q(Fe) = 0.4 - 2.8 x 10^23 s^-1. From derived column densities, the
Ni/Fe abundance ratio log10[Ni/Fe] = -0.15 +/- 0.07 deviates significantly from
solar abundance ratios, and it is consistent with the ratios observed in solar
system comets. Possible production and emission mechanisms are analyzed in
context of existing laboratory measurements. Based on the observed spatial
distributions, excellent fluorescence model agreement, and Ni/Fe ratio, our
findings support an origin consisting of a short-lived unknown parent followed
by fluorescence emission. Our models suggest that the strong heliocentric
velocity dependence of the fluorescence efficiencies can provide a meaningful
test of the physical process responsible for the Fe I and Ni I emission. | astro-ph_EP |
Solar wind dynamics around a comet - A 2D semi-analytical kinetic model: We aim at analytically modelling the solar wind proton trajectories during
their interaction with a partially ionised cometary atmosphere, not in terms of
bulk properties of the flow but in terms of single particle dynamics. We first
derive a generalised gyromotion, in which the electric field is reduced to its
motional component. Steady-state is assumed, and simplified models of the
cometary density and of the electron fluid are used to express the force
experienced by individual solar wind protons during the interaction. A
three-dimensional (3D) analytical expression of the gyration of two interacting
plasma beams is obtained. Applying it to a comet case, the force on protons is
always perpendicular to their velocity and has an amplitude proportional to
1/r^2. The solar wind deflection is obtained at any point in space. The
resulting picture presents a caustic of intersecting trajectories, and a
circular region is found that is completely free of particles. The particles do
not lose any kinetic energy and this absence of deceleration, together with the
solar wind deflection pattern and the presence of a solar wind ion cavity, is
in good agreement with the general results of the Rosetta mission. The
qualitative match between the model and the in situ data highlights how
dominant the motional electric field is throughout most of the interaction
region for the solar wind proton dynamics. The model provides a simple general
kinetic description of how momentum is transferred between these two
collisionless plasmas. It also shows the potential of this semi-analytical
model for a systematic quantitative comparison to the data. | astro-ph_EP |
Deep Pa$β$ Imaging of the Candidate Accreting Protoplanet AB Aur b: Giant planets grow by accreting gas through circumplanetary disks, but little
is known about the timescale and mechanisms involved in the planet assembly
process because few accreting protoplanets have been discovered. Recent visible
and infrared (IR) imaging revealed a potential accreting protoplanet within the
transition disk around the young intermediate-mass Herbig Ae star, AB Aurigae
(AB Aur). Additional imaging in H$\alpha$ probed for accretion and found
agreement between the line-to-continuum flux ratio of the star and companion,
raising the possibility that the emission source could be a compact disk
feature seen in scattered starlight. We present new deep Keck/NIRC2
high-contrast imaging of AB Aur to characterize emission in Pa$\beta$, another
accretion tracer less subject to extinction. Our narrow band observations reach
a 5$\sigma$ contrast of 9.6 mag at 0.6$''$, but we do not detect significant
emission at the expected location of the companion, nor from other any other
source in the system. Our upper limit on Pa$\beta$ emission suggests that if AB
Aur b is a protoplanet, it is not heavily accreting or accretion is stochastic
and was weak during the observations. | astro-ph_EP |
Expected Fragment Distribution from the First Interstellar Meteor CNEOS
2014-01-08: In 2014, the fireball of the first interstellar meteor CNEOS 2014-01-08 (IM1)
(Siraj & Loeb 2019), was detected off the northern coast of Papua New Guinea. A
recently announced ocean expedition will retrieve any extant fragments by
towing a magnetic sled across a 10 km x 10 km area of ocean floor approximately
300 km north of Manus Island (Siraj, Loeb, & Gallaudet 2022). We formulate a
model that includes both the probabilistic mass distribution of meteor
fragments immediately after the fragmentation event, the ablation of the
fragments, and the geographic distribution of post-ablation fragments along the
ground track trajectory of the bulk fragment cloud. We apply this model to IM1
to provide a heuristic estimate of the impactor's post-ablation fragment mass
distribution, constructed through a Monte Carlo simulation. We find between ~8%
and ~21% of fragments are expected to survive ablation with a mass $\geq$ .001
g, depending on the impactor's empirical yield strength. We also provide an
estimation for the geographic distribution of post-ablation fragments. | astro-ph_EP |
On the Earth's tidal perturbations for the LARES satellite: Frame dragging, one of the outstanding phenomena predicted by General
Relativity, is efficiently studied by means of the laser-ranged satellites
LARES, LAGEOS and LAGEOS 2. The accurate analysis of the orbital perturbations
of Earth's solid and ocean tides has been relevant for increasing the accuracy
in the test of frame-dragging using these three satellites. The Earth's tidal
perturbations acting on the LARES satellite are obtained for the 110
significant modes of corresponding Doodson number and are exhibited to enable
the comparison to those of the LAGEOS and LAGEOS-2 satellites. For LARES we
represent 29 perturbation modes for l=2,3,4 for ocean tides. | astro-ph_EP |
Three faint-source microlensing planets detected via resonant-caustic
channel: We conducted a project of reinvestigating the 2017--2019 microlensing data
collected by the high-cadence surveys with the aim of finding planets that were
missed due to the deviations of planetary signals from the typical form of
short-term anomalies. The project led us to find three planets including
KMT-2017-BLG-2509Lb, OGLE-2017-BLG-1099Lb, and OGLE-2019-BLG-0299Lb. The
lensing light curves of the events have a common characteristic that the
planetary signals were produced by the crossings of faint source stars over the
resonant caustics formed by giant planets located near the Einstein rings of
host stars. For all planetary events, the lensing solutions are uniquely
determined without any degeneracy. It is estimated that the host masses are in
the range of $0.45\lesssim M/M_\odot \lesssim 0.59$, which corresponds to early
M to late K dwarfs, and thus the host stars are less massive than the sun. On
the other hand, the planets, with masses in the range of $2.1\lesssim M/M_{\rm
J}\lesssim 6.2$, are heavier than the heaviest planet of the solar system, that
is, Jupiter. The planets in all systems lie beyond the snow lines of the hosts,
and thus the discovered planetary systems, together with many other
microlensing planetary systems, support that massive gas-giant planets are
commonplace around low-mass stars. We discuss the role of late-time
high-resolution imaging in clarifying resonant-image lenses with very faint
sources. | astro-ph_EP |
An enhanced slope in the transmission spectrum of the hot Jupiter
WASP-104b: We present the optical transmission spectrum of the hot Jupiter WASP-104b
based on one transit observed by the blue and red channels of the DBSP
spectrograph at the Palomar 200-inch telescope and 14 transits observed by the
MuSCAT2 four-channel imager at the 1.52 m Telescopio Carlos Sanchez. We also
analyse 45 additional K2 transits, after correcting for the flux contamination
from a companion star. Together with the transit light curves acquired by DBSP
and MuSCAT2, we are able to revise the system parameters and orbital ephemeris,
confirming that no transit timing variations exist. Our DBSP and MuSCAT2
combined transmission spectrum reveals an enhanced slope at wavelengths shorter
than 630 nm and suggests the presence of a cloud deck at longer wavelengths.
While the Bayesian spectral retrieval analyses favour a hazy atmosphere,
stellar spot contamination cannot be completely ruled out. Further evidence,
from transmission spectroscopy and detailed characterisation of the host star's
activity, is required to distinguish the physical origin of the enhanced slope. | astro-ph_EP |
Theoretical transmission spectra of exoplanet atmospheres with
hydrocarbon haze: Effect of creation, growth, and settling of haze particles.
I. Model description and first results: Recently, properties of exoplanet atmospheres have been constrained via
multi-wavelength transit observation, which measures an apparent decrease in
stellar brightness during planetary transit in front of its host star (called
transit depth). Sets of transit depths so far measured at different wavelengths
(called transmission spectra) are somewhat diverse: Some show steep spectral
slope features in the visible, some contain featureless spectra in the
near-infrared, some show distinct features from radiative absorption by gaseous
species. These facts infer the existence of haze in the atmospheres especially
of warm, relatively low-density super-Earths and mini-Neptunes. Previous
studies that addressed theoretical modeling of transmission spectra of
hydrogen-dominated atmospheres with haze used some assumed distribution and
size of haze particles. In this study, we model the atmospheric chemistry,
derive the spatial and size distributions of haze particles by simulating the
creation, growth and settling of hydrocarbon haze particles directly, and
develop transmission spectrum models of UV-irradiated, solar-abundance
atmospheres of close-in warm ($\sim$ 500 K) exoplanets. We find that the haze
is distributed in the atmosphere much more broadly than previously assumed and
consists of particles of various sizes. We also demonstrate that the observed
diversity of transmission spectra can be explained by the difference in the
production rate of haze monomers, which is related to the UV irradiation
intensity from host stars. | astro-ph_EP |
Aerosols optical properties in Titan's Detached Haze Layer before the
equinox: UV observations with Cassini ISS Narrow Angle Camera of Titan's detached haze
is an excellent tool to probe its aerosols content without being affected by
the gas or the multiple scattering. Unfortunately, its low extent in altitude
requires a high resolution calibration and limits the number of images
available in the Cassini dataset. However, we show that it is possible to
extract on each profile the local maximum of intensity of this layer and
confirm its stability at $500 \pm 8$ km during the 2005-2007 period for all
latitudes lower than 45$^\circ$N. Using the fractal aggregate scattering model
of Tomasko et al. (2008) and a single scattering radiative transfer model, it
is possible to derive the optical properties required to explain the
observations made at different phase angles. Our results indicates that the
aerosols have at least ten monomers of 60 nm radius, while the typical
tangential column number density is about $2\cdot 10^{10}$ agg.m$^{-2}$.
Moreover, we demonstrate that these properties are constant within the error
bars in the southern hemisphere of Titan over the observed time period. In the
northern hemisphere, the size of the aerosols tend to decrease relatively to
the southern hemisphere and are associated with a higher tangential opacity.
However, the lower number of observations available in this region due to the
orbital constraints is a limiting factor in the accuracy of these results.
Assuming a fixed homogeneous content we notice that the tangential opacity can
fluctuate up to a factor 3 among the observations at the equator. These
variations could be linked with short scale temporal and/or longitudinal events
changing the local density of the layer. | astro-ph_EP |
A Flat Inner Disk Model as an Alternative to the Kepler Dichotomy in the
Q1 to Q16 Planet Population: We use simulated planetary systems to model the planet multiplicity of Kepler
stars. Previous studies have underproduced single planet systems and invoked
the so called Kepler dichotomy, where the planet forming ability of a Kepler
star is dichotomous, producing either few or many transiting planets. In this
paper we show that the Kepler dichotomy is only required when the inner part of
planetary disks are just assumed to be flared. When the inner part of planetary
disks are flat, we reproduce the observed planet multiplicity of Kepler stars
without the need to invoke a dichotomy. We find that independent of the disk
model assumed, the mean number of planets per star is approximately 2 for
orbital periods between 3 and 200 days, and for planetary radii between 1 and 5
Earth radii. This contrasts with the Solar System where no planets occupy the
same parameter space. | astro-ph_EP |
Defining the Flora Family: Orbital Properties, Reflectance Properties
and Age: The Flora family resides in the densely populated inner main belt, bounded in
semimajor axis by the $\nu_6$ secular resonance and the Jupiter 3:1 mean motion
resonance. The presence of several large families that overlap dynamically with
the Floras (e.g., the Vesta, Baptistina, and Nysa-Polana families), and the
removal of a significant fraction of Floras via the nearby $\nu_6$ resonance
complicates the Flora family's distinction in both proper orbital elements and
reflectance properties. Here we use orbital information from the Asteroids
Dynamic Site, color information from the Sloan Digital Sky Survey, and albedo
information from the Wide-field Infrared Survey Explorer to obtain the median
orbital and reflectance properties of the Floras by sampling the core of the
family in multidimensional phase space. We find the median Flora SDSS colors to
be $a^*$ = 0.126 $\pm$ 0.007 and $i-z = -0.037 \pm 0.007$; the median Flora
albedo is $p_V$ = 0.291 $\pm$ 0.012. These properties allow us to define ranges
for the Flora family in orbital and reflectance properties, as required for a
detailed dynamical study. We use the young Karin family, for which we have an
age determined via direct backward integration of members' orbits, to calibrate
the Yarkovsky drift rates for the Flora family without having to estimate the
Floras' material properties. The size-dependent dispersion of the Flora members
in semimajor axis (the "V" plot) then yields an age for the family of
$910^{+160}_{-120}$ My, with the uncertainty dominated by the uncertainty in
the material properties of the family members (e.g., density and surface
thermal properties). We discuss the effects on our age estimate of two
independent processes that both introduce obliquity variations among the family
members on short (My) timescales: 1) the capture of Flora members in spin-orbit
resonance, and 2) YORP-driven obliquity variation. | astro-ph_EP |
HAT-P-65b and HAT-P-66b: Two Transiting Inflated Hot Jupiters and
Observational Evidence for the Re-Inflation of Close-In Giant Planets: We present the discovery of the transiting exoplanets HAT-P-65b and
HAT-P-66b, with orbital periods of 2.6055 d and 2.9721 d, masses of $0.527 \pm
0.083$ M$_{J}$ and $0.783 \pm 0.057$ M$_{J}$ and inflated radii of $1.89 \pm
0.13$ R$_{J}$ and $1.59^{+0.16}_{-0.10}$ R$_{J}$, respectively. They orbit
moderately bright ($V=13.145 \pm 0.029$, and $V=12.993 \pm 0.052$) stars of
mass $1.212 \pm 0.050$ M$_{\odot}$ and $1.255^{+0.107}_{-0.054}$ M$_{\odot}$.
The stars are at the main sequence turnoff. While it is well known that the
radii of close-in giant planets are correlated with their equilibrium
temperatures, whether or not the radii of planets increase in time as their
hosts evolve and become more luminous is an open question. Looking at the
broader sample of well-characterized close-in transiting giant planets, we find
that there is a statistically significant correlation between planetary radii
and the fractional ages of their host stars, with a false alarm probability of
only 0.0041%. We find that the correlation between the radii of planets and the
fractional ages of their hosts is fully explained by the known correlation
between planetary radii and their present day equilibrium temperatures, however
if the zero-age main sequence equilibrium temperature is used in place of the
present day equilibrium temperature then a correlation with age must also be
included to explain the planetary radii. This suggests that, after contracting
during the pre-main-sequence, close-in giant planets are re-inflated over time
due to the increasing level of irradiation received from their host stars.
Prior theoretical work indicates that such a dynamic response to irradiation
requires a significant fraction of the incident energy to be deposited deep
within the planetary interiors. | astro-ph_EP |
Origin of the peculiar eccentricity distribution of the inner cold
Kuiper belt: Dawson and Murray-Clay (2012) pointed out that the inner part of the cold
population in the Kuiper belt (that with semi major axis a<43.5 AU) has orbital
eccentricities significantly smaller than the limit imposed by stability
constraints. Here, we confirm their result by looking at the orbital
distribution and stability properties in proper element space. We show that the
observed distribution could have been produced by the slow sweeping of the 4/7
mean motion resonance with Neptune that accompanied the end of Neptune's
migration process. The orbital distribution of the hot Kuiper belt is not
significantly affected in this process, for the reasons discussed in the main
text. Therefore, the peculiar eccentricity distribution of the inner cold
population can not be unequivocally interpreted as evidence that the cold
population formed in-situ and was only moderately excited in eccentricity; it
can simply be the signature of Neptune's radial motion, starting from a
moderately eccentric orbit. We discuss how this agrees with a scenario of giant
planet evolution following a dynamical instability and, possibly, with the
radial transport of the cold population. | astro-ph_EP |
Stellar Spin-Orbit Alignment for Kepler-9, a Multi-transiting Planetary
system with Two Outer Planets Near 2:1 Resonance: We present spectroscopic measurements of the Rossiter-McLaughlin effect for
the planet b of Kepler-9 multi-transiting planet system. The resulting
sky-projected spin-orbit angle is $\lambda=-13^{\circ} \pm 16^{\circ}$, which
favors an aligned system and strongly disfavors highly misaligned, polar, and
retrograde orbits. Including Kepler-9, there are now a total of 4
Rossiter-McLaughlin effect measurements for multiplanet systems, all of which
are consistent with spin-orbit alignment. | astro-ph_EP |
An Observational Diagnostic for Distinguishing Between Clouds and Haze
in Hot Exoplanet Atmospheres: The nature of aerosols in hot exoplanet atmospheres is one of the primary
vexing questions facing the exoplanet field. The complex chemistry, multiple
formation pathways, and lack of easily identifiable spectral features
associated with aerosols make it especially challenging to constrain their key
properties. We propose a transmission spectroscopy technique to identify the
primary aerosol formation mechanism for the most highly irradiated hot Jupiters
(HIHJs). The technique is based on the expectation that the two key types of
aerosols -- photochemically generated hazes and equilibrium condensate clouds
-- are expected to form and persist in different regions of a highly irradiated
planet's atmosphere. Haze can only be produced on the permanent daysides of
tidally-locked hot Jupiters, and will be carried downwind by atmospheric
dynamics to the evening terminator (seen as the trailing limb during transit).
Clouds can only form in cooler regions on the night side and morning terminator
of HIHJs (seen as the leading limb during transit). Because opposite limbs are
expected to be impacted by different types of aerosols, ingress and egress
spectra, which primarily probe opposing sides of the planet, will reveal the
dominant aerosol formation mechanism. We show that the benchmark HIHJ,
WASP-121b, has a transmission spectrum consistent with partial aerosol coverage
and that ingress-egress spectroscopy would constrain the location and formation
mechanism of those aerosols. In general, using this diagnostic we find that
observations with JWST and potentially with HST should be able to distinguish
between clouds and haze for currently known HIHJs. | astro-ph_EP |
Exoplanetary Spin-Orbit Alignment: Results from the Ensemble of
Rossiter-McLaughlin Observations: One possible diagnostic of planet formation, orbital migration, and tidal
evolution is the angle psi between a planet's orbital axis and the spin axis of
its parent star. In general, psi cannot be measured, but for transiting planets
one can measure the angle lambda between the sky projections of the two axes
via the Rossiter-McLaughlin effect. Here, we show how to combine measurements
of lambda in different systems to derive statistical constraints on psi. We
apply the method to 11 published measurements of lambda, using two different
single-parameter distributions to describe the ensemble. First, assuming a
Rayleigh distribution (or more precisely, a Fisher distribution on a sphere),
we find that the peak value is less than 22 degrees with 95% confidence.
Second, assuming a fraction f of the orbits have random orientations relative
to the stars, and the remaining fraction (1-f) are perfectly aligned, we find
f<0.36 with 95% confidence. This latter model fits the data better than the
Rayleigh distribution, mainly because the XO-3 system was found to be strongly
misaligned while the other 10 systems are consistent with perfect alignment. If
the XO-3 result proves robust, then our results may be interpreted as evidence
for two distinct modes of planet migration. | astro-ph_EP |
Crowding Out of Giants by Dwarfs: An Origin for the Lack of Companion
Planets in Hot Jupiter Systems: We investigate formation of close-in terrestrial planets from planetary
embryos under the influence of a hot Jupiter (HJ) using gravitational N-body
simulations that include gravitational interactions between the gas disk and
the terrestrial planet (e.g., type I migration). Our simulations show that
several terrestrial planets efficiently form outside the orbit of the HJ,
making a chain of planets, and all of them gravitationally interact directly or
indirectly with the HJ through resonance, which leads to inward migration of
the HJ. We call this mechanism of induced migration of the HJ as "crowding
out." The HJ is eventually lost by collision with the central star, and only
several terrestrial planets remain. We also find that the efficiency of the
crowding-out effect depends on model parameters; for example, the heavier the
disk is, the more efficient the crowding out is. When planet formation occurs
in a massive disk, the HJ can be lost to the central star and is never
observed. On the other hand, for a less massive disk, the HJ and terrestrial
planets can coexist; however, the companion planets can be below the detection
limit of current observations. In both cases, systems with the HJ and
terrestrial planets have little chance for detection. Therefore, our model
naturally explains the lack of companion planets in HJ systems regardless of
the disk mass. In effect, our model provide a theoretical prediction for future
observations; additional planets can be discovered just outside the HJ, and
their masses should generally be small. | astro-ph_EP |
Transit detections of extrasolar planets around main-sequence stars - I.
Sky maps for hot Jupiters: The findings of more than 350 extrasolar planets, most of them nontransiting
Hot Jupiters, have revealed correlations between the metallicity of the
main-sequence (MS) host stars and planetary incidence. This connection can be
used to calculate the planet formation probability around other stars, not yet
known to have planetary companions. We locate the promising spots for current
transit surveys on the celestial plane and strive for absolute values of the
expected number of transits in general. We used data of the Tycho catalog for
about 1 million objects to locate all the stars with 0m < m_V < 11.5m on the
celestial plane. We took several empirical relations between the parameters
listed in the Tycho catalog, such as distance to Earth, m_V, and (B-V), and
those parameters needed to account for the probability of a star to host an
observable, transiting exoplanet. The empirical relations between stellar
metallicity and planet occurrence combined with geometrical considerations were
used to yield transit probabilities for the MS stars in the Tycho catalog.
Magnitude variations in the FOV were simulated to test whether this
fluctuations would be detected by BEST, XO, SuperWASP and HATNet. We present a
sky map of the expected number of Hot Jupiter transit events on the basis of
the Tycho catalog. The comparison between the considered transit surveys yields
significantly differing maps of the expected transit detections. The
sky-integrated magnitude distribution predicts 20 Hot Jupiter transits with
orbital periods between 1.5 d and 50 d and m_V < 8m, of which two are currently
known. In total, we expect 3412 Hot Jupiter transits to occur in front of MS
stars within the given magnitude range. The most promising observing site on
Earth is at latitude = -1. | astro-ph_EP |
Neptune on tiptoes: dynamical histories that preserve the cold classical
Kuiper belt: The current dynamical structure of the Kuiper belt was shaped by the orbital
evolution of the giant planets, especially Neptune, during the era following
planet formation, when the giant planets may have undergone planet-planet
scattering and/or planetesimal-driven migration. Numerical simulations of this
process, while reproducing many properties of the belt, fail to generate the
high inclinations and eccentricities observed for some objects while
maintaining the observed dynamically "cold" population. We present the first of
a three-part parameter study of how different dynamical histories of Neptune
sculpt the planetesimal disk. Here we identify which dynamical histories allow
an in situ planetesimal disk to remain dynamically cold, becoming today's cold
Kuiper belt population. We find that if Neptune undergoes a period of elevated
eccentricity and/or inclination, it secularly excites the eccentricities and
inclinations of the planetesimal disk. We demonstrate that there are several
well-defined regimes for this secular excitation, depending on the relative
timescales of Neptune's migration, the damping of Neptune's orbital inclination
and/or eccentricity, and the secular evolution of the planetesimals. We model
this secular excitation analytically in each regime, allowing for a thorough
exploration of parameter space. Neptune's eccentricity and inclination can
remain high for a limited amount of time without disrupting the cold classical
belt. In the regime of slow damping and slow migration, if Neptune is located
(for example) at 20 AU, then its eccentricity must stay below 0.18 and its
inclination below 6{\deg}. | astro-ph_EP |
Gran Telescopio Canarias OSIRIS Transiting Exoplanet Atmospheric Survey:
Detection of potassium in XO-2b from narrowband spectrophotometry: We present Gran Telescopio Canarias (GTC) optical transit narrow-band
photometry of the hot-Jupiter exoplanet XO-2b using the OSIRIS instrument. This
unique instrument has the capabilities to deliver high cadence narrow-band
photometric lightcurves, allowing us to probe the atmospheric composition of
hot Jupiters from the ground. The observations were taken during three transit
events which cover four wavelengths at spectral resolutions near 500, necessary
for observing atmospheric features, and have near-photon limited sub-mmag
precisions. Precision narrow-band photometry on a large aperture telescope
allows for atmospheric transmission spectral features to be observed for
exoplanets around much fainter stars than those of the well studied targets
HD209458b and HD189733b, providing access to the majority of known transiting
planets. For XO-2b, we measure planet-to-star radius contrasts of
R_pl/R_star=0.10508+/-0.00052 at 6792 Ang, 0.10640+/-0.00058 at 7582 Ang, and
0.10686+/-0.00060 at 7664.9 Ang, and 0.10362+/-0.00051 at 8839 Ang. These
measurements reveal significant spectral features at two wavelengths, with an
absorption level of 0.067+/-0.016% at 7664.9 Ang due to atmospheric potassium
in the line core (a 4.1-sigma significance level), and an absorption level of
0.058+/-0.016% at 7582 Ang, (a 3.6-sigma significance level). When comparing
our measurements to hot-Jupiter atmospheric models, we find good agreement with
models which are dominated in the optical by alkali metals. This is the first
evidence for potassium in an extrasolar planet, an element that has long been
theorized along with sodium to be a dominant source of opacity at optical
wavelengths for hot Jupiters. | astro-ph_EP |
Vertically resolved magma ocean-protoatmosphere evolution: H$_2$,
H$_2$O, CO$_2$, CH$_4$, CO, O$_2$, and N$_2$ as primary absorbers: The earliest atmospheres of rocky planets originate from extensive volatile
release during magma ocean epochs that occur during assembly of the planet.
These establish the initial distribution of the major volatile elements between
different chemical reservoirs that subsequently evolve via geological cycles.
Current theoretical techniques are limited in exploring the anticipated range
of compositional and thermal scenarios of early planetary evolution, even
though these are of prime importance to aid astronomical inferences on the
environmental context and geological history of extrasolar planets. Here, we
present a coupled numerical framework that links an evolutionary,
vertically-resolved model of the planetary silicate mantle with a
radiative-convective model of the atmosphere. Using this method we investigate
the early evolution of idealized Earth-sized rocky planets with end-member,
clear-sky atmospheres dominated by either H$_2$, H$_2$O, CO$_2$, CH$_4$, CO,
O$_2$, or N$_2$. We find central metrics of early planetary evolution, such as
energy gradient, sequence of mantle solidification, surface pressure, or
vertical stratification of the atmosphere, to be intimately controlled by the
dominant volatile and outgassing history of the planet. Thermal sequences fall
into three general classes with increasing cooling timescale: CO, N$_2$, and
O$_2$ with minimal effect, H$_2$O, CO$_2$, and CH$_4$ with intermediate
influence, and H$_2$ with several orders of magnitude increase in
solidification time and atmosphere vertical stratification. Our numerical
experiments exemplify the capabilities of the presented modeling framework and
link the interior and atmospheric evolution of rocky exoplanets with
multi-wavelength astronomical observations. | astro-ph_EP |
A Dynamical Analysis of the Kepler-80 System of Five Transiting Planets: Kepler has discovered hundreds of systems with multiple transiting exoplanets
which hold tremendous potential both individually and collectively for
understanding the formation and evolution of planetary systems. Many of these
systems consist of multiple small planets with periods less than ~50 days known
as Systems with Tightly-spaced Inner Planets, or STIPs. One especially
intriguing STIP, Kepler-80 (KOI-500), contains five transiting planets: f, d,
e, b, and c with periods of 1.0, 3.1, 4.6, 7.1, 9.5 days, respectively. We
provide measurements of transit times and a transit timing variation (TTV)
dynamical analysis. We find that TTVs cannot reliably detect eccentricities for
this system, though mass estimates are not affected. Restricting the
eccentricity to a reasonable range, we infer masses for the outer four planets
(d, e, b, and c) to be $6.75^{+0.69}_{-0.51}$, $4.13^{+0.81}_{-0.95}$,
$6.93^{+1.05}_{-0.70}$, and $6.74^{+1.23}_{-0.86}$ Earth masses, respectively.
The similar masses but different radii are consistent with terrestrial
compositions for d and e and $\sim$2% H/He envelopes for b and c. We confirm
that the outer four planets are in a rare dynamical configuration with four
interconnected three-body resonances that are librating with few degree
amplitudes. We present a formation model that can reproduce the observed
configuration by starting with a multi-resonant chain and introducing
dissipation. Overall, the information-rich Kepler-80 planets provide an
important perspective into exoplanetary systems. | astro-ph_EP |
2001 QR322: a dynamically unstable Neptune Trojan?: Since early work on the stability of the first Neptunian Trojan, 2001 QR322,
suggested that it was a dynamically stable, primordial body, it has been
assumed this applies to both that object, and its more recently discovered
brethren. However, it seems that things are no longer so clear cut. In this
work, we present the results of detailed dynamical simulations of the orbital
behaviour of 2001 QR322. Using an ephemeris for the object that has
significantly improved since earlier works, we follow the evolution of 19683
test particles, placed on orbits within the observational error ellipse of 2001
QR322's orbit, for a period of 1 Gyr. We find that majority of these "clones"
of 2001 QR322 are dynamically unstable, exhibiting a near-exponential decay
from both the Neptunian Trojan cloud (decay halflife ~550 Myr) and the Solar
system (decay halflife ~590 Myr). The stability of the object within Neptune's
Trojan cloud is found to be strongly dependent on the initial semi-major axis
used, with those objects located at semimajor axis equal or greater than 30.30
AU being significantly less stable than those interior to this value, as a
result of their having initial libration amplitudes very close to a critical
threshold dividing regular and irregular motion, located at ~70-75 deg (full
extent of angular motion). This result suggests that, if 2001 QR322 is a
primordial Neptunian Trojan, it must be a representative of a population that
was once significantly larger than that we see today, and adds weight to the
idea that the Neptune Trojans may represent a significant source of objects
moving on unstable orbits between the giant planets (the Centaurs). | astro-ph_EP |
Expanding Mars Climate Modeling: Interpretable Machine Learning for
Modeling MSL Relative Humidity: For the past several decades, numerous attempts have been made to model the
climate of Mars with extensive studies focusing on the planet's dynamics and
the understanding of its climate. While physical modeling and data assimilation
approaches have made significant progress, uncertainties persist in
comprehensively capturing and modeling the complexities of Martian climate. In
this work, we propose a novel approach to Martian climate modeling by
leveraging machine learning techniques that have shown remarkable success in
Earth climate modeling. Our study presents a deep neural network designed to
accurately model relative humidity in Gale Crater, as measured by NASA's Mars
Science Laboratory ``Curiosity'' rover. By utilizing simulated meteorological
variables produced by the Mars Planetary Climate Model, a robust Global
Circulation Model, our model accurately predicts relative humidity with a mean
error of 3\% and an $R^2$ score of 0.92. Furthermore, we present an approach to
predict quantile ranges of relative humidity, catering to applications that
require a range of values. To address the challenge of interpretability
associated with machine learning models, we utilize an interpretable model
architecture and conduct an in-depth analysis of its internal mechanisms and
decision making processes. We find that our neural network can effectively
model relative humidity at Gale crater using a few meteorological variables,
with the monthly mean surface H$_2$O layer, planetary boundary layer height,
convective wind speed, and solar zenith angle being the primary contributors to
the model predictions. In addition to providing a fast and efficient method to
modeling climate variables on Mars, this modeling approach can also be used to
expand on current datasets by filling spatial and temporal gaps in
observations. | astro-ph_EP |
Mass-Radius Relation for Rocky Planets based on PREM: Several small dense exoplanets are now known, inviting comparisons to Earth
and Venus. Such comparisons require translating their masses and sizes to
composition models of evolved multi-layer-interior planets. Such theoretical
models rely on our understanding of the Earth's interior, as well as
independently derived equations of state (EOS), but have so far not involved
direct extrapolations from Earth's seismic model -PREM. In order to facilitate
more detailed compositional comparisons between small exoplanets and the Earth,
we derive here a semi-empirical mass-radius relation for two-layer rocky
planets based on PREM: ${\frac{R}{R_\oplus}} = (1.07-0.21\cdot \text{CMF})\cdot
(\frac{M}{M_\oplus})^{1/3.7}$, where CMF stands for Core Mass Fraction. It is
applicable to 1$\sim$8 M$_{\oplus}$ and CMF of 0.0$\sim$0.4. Applying this
formula to Earth and Venus and several known small exoplanets with radii and
masses measured to better than $\sim$30\% precision gives a CMF fit of
$0.26\pm0.07$. | astro-ph_EP |
Orbit injection of planet-crossing asteroids: Solar system Centaurs originate in transneptunian space from where planet
orbit crossing events inject their orbits inside the giant planets' domain.
Here, we examine this injection process in the three-body problem by studying
the orbital evolution of transneptunian asteroids located at Neptune's
collision singularity as a function of the Tisserand invariant, T. Two
injection modes are found, one for T>0.1, or equivalently prograde inclinations
far from the planet, where unstable motion dominates injection, and another for
T<= 0.1, or equivalently polar and retrograde inclinations far from the planet,
where stable motion dominates injection. The injection modes are independent of
the initial semi-major axis and the dynamical time at the collision
singularity. The simulations uncovered a region in the polar corridor where the
dynamical time exceeds the solar system's age suggesting the possibility of
long-lived primordial polar transneptunian reservoirs that supply Centaurs to
the giant planets' domain. | astro-ph_EP |
On a Possible Giant Impact Origin for the Colorado Plateau: It is proposed and substantiated that an extraterrestrial object of the
approximate size and mass of Planet Mars, impacting the Earth in grazing
incidence along an approximately N-NE to S-SW route with respect to the current
orientation of the North America continent, at about 750 million years ago (750
Ma), is likely to be the direct cause of a chain of events which led to the
rifting of the Rodinia supercontinent and the severing of the foundation of the
Colorado Plateau from its surrounding craton. It is further argued that the
impactor was most likely a rogue exoplanet, which originated from one of the
past crossings of our Solar System through the Galactic spiral arms, during the
Sun's orbital motion around the center of the Milky Way Galaxy. New advances in
galactic dynamics have shown that the sites of galactic spiral arms are
locations of density-wave collisionless shocks. The perturbations from such
shocks are known to lead to the formation of massive stars, which evolve
quickly and die as supernovae. The blastwaves from supernova explosions, in
addition to the spiral-arm collisionless shocks themselves, could perturb the
orbits of the streaming disk matter, occasionally producing rogue exoplanets
that can reach the inner confines of our Solar System. The similarity of the
period of spiral-arm crossings of our Solar System, with the approximate period
of major extinction events in the Phanerozoic Eon of the Earth's history, as
well as with the (half) period of the supercontinent cycle, indicates that the
global environment of the Milky Way Galaxy may have played a major role in
initiating Earth's tectonic activities. | astro-ph_EP |
TraMoS project III: Improved physical parameters, timing analysis, and
star-spot modelling of the WASP-4b exoplanet system from 38 transit
observations: We report twelve new transit observations of the exoplanet WASP-4b from the
Transit Monitoring in the South Project (TraMoS) project. These transits are
combined with all previously published transit data for this planet to provide
an improved radius measurement of Rp = 1.395 +- 0.022 Rjup and improved transit
ephemerides. In a new homogeneous analysis in search for Transit Timing
Variations (TTVs) we find no evidence of those with RMS amplitudes larger than
20 seconds over a 4-year time span. This lack of TTVs rules out the presence of
additional planets in the system with masses larger than about 2.5 M_earth, 2.0
M_earth, and 1.0 M_earth around the 1:2, 5:3 and 2:1 orbital resonances. Our
search for the variation of other parameters, such as orbital inclination and
transit depth also yields negative results over the total time span of the
transit observations. Finally we perform a simple study of stellar spots
configurations of the system and conclude that the star rotational period is
about 34 days. | astro-ph_EP |
Very wide companion fraction from Gaia DR2: a weak or no enhancement for
hot jupiter hosts, and a strong enhancement for contact binaries: There is an ongoing debate on whether hot jupiter hosts are more likely to be
found in wide binaries with separations of $\gtrsim 100$ AU. In this paper, we
search for comoving, very wide companions with separations of $10^3-10^4$ AU
for hot jupiter hosts and main-sequence contact binaries in Gaia DR2, and
compare the very wide companion fractions with their object-by-object-matched
field star samples. We find that $11.9\pm 2.5$% of hot jupiter hosts and
$14.1\pm 1.0$% of contact binaries have companions at separations of
$10^3-10^4$ AU. While the very wide companion fraction of hot jupiter hosts is
a factor of $1.9\pm0.5$ larger than their matched field star sample, it is
consistent, within $\sim1\sigma$, with that of matched field stars if the
matching is only with field stars without close companions (within $\sim50$ AU)
as is the case for hot jupiter hosts. The very wide companion fraction of
contact binaries is a factor of $3.1\pm0.5$ larger than their matched field
star sample, suggesting that the formation and evolution of contact binaries
are either tied to or correlated with the presence of wide companions. In
contrast, the weak enhancement of very wide companion fraction for hot jupiter
hosts implies that the formation of hot jupiters is not as sensitive to those
environment properties. Our results also hint that the occurrence rates of dual
hot jupiter hosts and dual contact binaries may be higher than the expected
values from random pairing of field stars, which may be due to their underlying
metallicity and age dependence. | astro-ph_EP |
NELIOTA Lunar Impact Flash Detection and Event Validation: NELIOTA (NEO Lunar Impacts and Optical TrAnsients) is an ESA-funded lunar
monitoring project, which aims to determine the size-frequency distribution of
small Near-Earth Objects (NEOs) via detection of impact flashes on the surface
of the Moon. A prime focus, high-speed, twin-camera system providing
simultaneous observations in two photometric bands at a rate of 30
frames-per-second on the 1.2 m Kryoneri telescope of the National Observatory
of Athens was commissioned for this purpose. A dedicated software processes the
images and automatically detects candidate lunar impact flashes, which are then
validated by an expert user. The four year observing campaign began in February
2017 and has so far detected more than 40 lunar impact events. The software
routinely detects satellites, which typically appear as streaks or dots
crossing the lunar disk. To avoid confusing these events with real flashes, we
check different available catalogs with spacecraft orbital information and
exclude spacecraft identifications. | astro-ph_EP |
The impact of the Kasatochi eruption on the Moon's illumination during
the August 2008 lunar eclipse: The Moon's changeable aspect during a lunar eclipse is largely attributable
to variations in the refracted unscattered sunlight absorbed by the terrestrial
atmosphere that occur as the satellite crosses the Earth's shadow. The
contribution to the Moon's aspect from sunlight scattered at the Earth's
terminator is generally deemed minor. However, our analysis of a published
spectrum of the 16 August 2008 lunar eclipse shows that diffuse sunlight is a
major component of the measured spectrum at wavelengths shorter than 600 nm.
The conclusion is supported by two distinct features, namely the spectrum's
tail at short wavelengths and the unequal absorption by an oxygen collisional
complex at two nearby bands. Our findings are consistent with the presence of
the volcanic cloud reported at high northern latitudes following the 7-8 August
2008 eruption in Alaska of the Kasatochi volcano. The cloud both attenuates the
unscattered sunlight and enhances moderately the scattered component, thus
modifying the contrast between the two contributions. | astro-ph_EP |
TESS Input Catalog versions 8.1 and 8.2: Phantoms in the 8.0 Catalog and
How to Handle Them: We define various types of "phantom" stars that may appear in the TESS Input
Catalog (TIC), and provide examples and lists of currently known cases. We
present a methodology that can be used to check for phantoms around any object
of interest in the TIC, and we present an approach for correcting the
TIC-reported flux contamination factors accordingly. We checked all 2077 TESS
Objects of Interest (TOIs) known as of July 21st 2020 (Sectors 1 to 24) and
sent corrections for 291 stars to MAST where they are integrated into the
publicly available TIC-8, updating it to TIC 8.1. We used the experience gained
to construct an all-sky algorithm searching for "phantoms" which led to 34
million updates integrated into TIC 8.2. | astro-ph_EP |
Tidal Heating Models for the Radii of the Inflated Transiting Giant
Planets WASP-4b, WASP-6b, WASP-12b, and TrES-4: In order to explain the inflated radii of some transiting extrasolar giant
planets, we investigate a tidal heating scenario for the inflated planets
WASP-4b, WASP-6b, WASP-12b, WASP-15b, and TrES-4. To do so, we assume that they
retain a nonzero eccentricity, possibly by dint of continuing interaction with
a third body. We calculate the amount of extra heating in the envelope that is
then required to fit the radius of each planet, and we explore how this
additional power depends on the planetary atmospheric opacity and on the mass
of a heavy-element central core. There is a degeneracy between the core mass
$M_{\rm core}$ and the heating $\dot{E}_{\rm heating}$. Therefore, in the case
of tidal heating, there is for each planet a range of the couple $\{M_{\rm
core},e^2/Q'_p\}$ that can lead to the same radius, where $Q'_p$ is the tidal
dissipation factor and $e$ is the eccentricity. With this in mind, we also
investigate the case of the non-inflated planet HAT-P-12b, which can admit
solutions combining a heavy-element core and tidal heating. A substantial
improvement of the measured eccentricities of such planetary systems could
simplify this degeneracy by linking the two unknown parameters $\{M_{\rm
core},Q'_p\}$. Further independent constraints on either of these parameters
would, through our calculations, constrain the other. | astro-ph_EP |
The Solar Twin Planet Search. V. Close-in, low-mass planet candidates
and evidence of planet accretion in the solar twin HIP 68468: [Methods]. We obtained high-precision radial velocities with HARPS on the ESO
3.6 m telescope and determined precise stellar elemental abundances (~0.01 dex)
using MIKE spectra on the Magellan 6.5m telescope. [Results]. Our data indicate
the presence of a planet with a minimum mass of 26 Earth masses around the
solar twin HIP 68468. The planet is a super-Neptune, but unlike the distant
Neptune in our solar system (30 AU), HIP 68468c is close-in, with a semi-major
axis of 0.66 AU, similar to that of Venus. The data also suggest the presence
of a super-Earth with a minimum mass of 2.9 Earth masses at 0.03 AU; if the
planet is confirmed, it will be the fifth least massive radial velocity planet
discovery to date and the first super-Earth around a solar twin. Both
isochrones (5.9 Gyr) and the abundance ratio [Y/Mg] (6.4 Gyr) indicate an age
of about 6 billion years. The star is enhanced in refractory elements when
compared to the Sun, and the refractory enrichment is even stronger after
corrections for Galactic chemical evolution. We determined a NLTE Li abundance
of 1.52 dex, which is four times higher than what would be expected for the age
of HIP 68468. The older age is also supported by the low log(R'HK) (-5.05) and
low jitter. Engulfment of a rocky planet of 6 Earth masses can explain the
enhancement in both lithium and the refractory elements. [Conclusions]. The
super-Neptune planet candidate is too massive for in situ formation, and
therefore its current location is most likely the result of planet migration
that could also have driven other planets towards its host star, enhancing thus
the abundance of lithium and refractory elements in HIP 68468. The intriguing
evidence of planet accretion warrants further observations to verify the
existence of the planets that are indicated by our data and to better constrain
the nature of the planetary system around this unique star. | astro-ph_EP |
A Twilight Search for Atiras, Vatiras and Co-orbital Asteroids:
Preliminary Results: Near-Earth Objects (NEOs) that orbit the Sun on or within Earth's orbit are
tricky to detect for Earth-based observers due to their proximity to the Sun in
the sky. These small bodies hold clues to the dynamical history of the inner
solar system as well as the physical evolution of planetesimals in extreme
environments. Populations in this region include the Atira and Vatira
asteroids, as well as Venus and Earth co-orbital asteroids. Here we present a
twilight search for these small bodies, conducted using the 1.2-m Oschin
Schmidt and the Zwicky Transient Facility (ZTF) camera at Palomar Observatory.
The ZTF twilight survey operates at solar elongations down to $35^\circ$ with
limiting magnitude of $r=19.5$. During a total of 40 evening sessions and 62
morning sessions conducted between 2018 November 15 and 2019 June 23, we
detected 6 Atiras, including 2 new discoveries 2019 AQ$_3$ and 2019 LF$_6$, but
no Vatiras or Earth/Venus co-orbital asteroids. NEO population models show that
these new discoveries are likely only the tip of the iceberg, with the bulk of
the population yet to be found. The population models also suggest that we have
only detected 5--$7\%$ of the $H<20$ Atira population over the 7-month survey.
Co-orbital asteroids are smaller in diameters and require deeper surveys. A
systematic and efficient survey of the near-Sun region will require deeper
searches and/or facilities that can operate at small solar elongations. | astro-ph_EP |
Gaussian Processes and Nested Sampling Applied to Kepler's Small
Long-period Exoplanet Candidates: There are more than 5000 confirmed and validated planets beyond the solar
system to date, more than half of which were discovered by NASA's Kepler
mission. The catalog of Kepler's exoplanet candidates has only been extensively
analyzed under the assumption of white noise (i.i.d. Gaussian), which breaks
down on timescales longer than a day due to correlated noise (point-to-point
correlation) from stellar variability and instrumental effects. Statistical
validation of candidate transit events becomes increasingly difficult when they
are contaminated by this form of correlated noise, especially in the
low-signal-to-noise (S/N) regimes occupied by Earth--Sun and Venus--Sun
analogs. To diagnose small long-period, low-S/N putative transit signatures
with few (roughly 3--9) observed transit-like events (e.g., Earth--Sun
analogs), we model Kepler's photometric data as noise, treated as a Gaussian
process, with and without the inclusion of a transit model. Nested sampling
algorithms from the Python UltraNest package recover model evidences and
maximum a posteriori parameter sets, allowing us to disposition transit
signatures as either planet candidates or false alarms within a Bayesian
framework. | astro-ph_EP |
Transit Timing Observations from Kepler: VI. Potentially interesting
candidate systems from Fourier-based statistical tests: We analyze the deviations of transit times from a linear ephemeris for the
Kepler Objects of Interest (KOI) through Quarter six (Q6) of science data. We
conduct two statistical tests for all KOIs and a related statistical test for
all pairs of KOIs in multi-transiting systems. These tests identify several
systems which show potentially interesting transit timing variations (TTVs).
Strong TTV systems have been valuable for the confirmation of planets and their
mass measurements. Many of the systems identified in this study should prove
fruitful for detailed TTV studies. | astro-ph_EP |
The first super-Earth Detection from the High Cadence and High Radial
Velocity Precision Dharma Planet Survey: The Dharma Planet Survey (DPS) aims to monitor about 150 nearby very bright
FGKM dwarfs (within 50 pc) during 2016$-$2020 for low-mass planet detection and
characterization using the TOU very high resolution optical spectrograph
(R$\approx$100,000, 380-900nm). TOU was initially mounted to the 2-m Automatic
Spectroscopic Telescope at Fairborn Observatory in 2013-2015 to conduct a pilot
survey, then moved to the dedicated 50-inch automatic telescope on Mt. Lemmon
in 2016 to launch the survey. Here we report the first planet detection from
DPS, a super-Earth candidate orbiting a bright K dwarf star, HD 26965. It is
the second brightest star ($V=4.4$ mag) on the sky with a super-Earth
candidate. The planet candidate has a mass of 8.47$\pm0.47M_{\rm Earth}$,
period of $42.38\pm0.01$ d, and eccentricity of $0.04^{+0.05}_{-0.03}$. This RV
signal was independently detected by Diaz et al. (2018), but they could not
confirm if the signal is from a planet or from stellar activity. The orbital
period of the planet is close to the rotation period of the star (39$-$44.5 d)
measured from stellar activity indicators. Our high precision photometric
campaign and line bisector analysis of this star do not find any significant
variations at the orbital period. Stellar RV jitters modeled from star spots
and convection inhibition are also not strong enough to explain the RV signal
detected. After further comparing RV data from the star's active magnetic phase
and quiet magnetic phase, we conclude that the RV signal is due to
planetary-reflex motion and not stellar activity. | astro-ph_EP |
Dust Ejection from Planetary Bodies by Temperature Gradients: Laboratory
Experiments: Laboratory experiments show that dusty bodies in a gaseous environment eject
dust particles if they are illuminated. We find that even more intense dust
eruptions occur when the light source is turned off. We attribute this to a
compression of gas by thermal creep in response to the changing temperature
gradients in the top dust layers. The effect is studied at a light flux of 13
kW/(m*m) and 1 mbar ambient pressure. The effect is applicable to
protoplanetary disks and Mars. In the inner part of protoplanetary disks,
planetesimals can be eroded especially at the terminator of a rotating body.
This leads to the production of dust which can then be transported towards the
disk edges or the outer disk regions. The generated dust might constitute a
significant fraction of the warm dust observed in extrasolar protoplanetary
disks. We estimate erosion rates of about 1 kg/s for 100 m parent bodies. The
dust might also contribute to subsequent planetary growth in different
locations or on existing protoplanets which are large enough not to be
susceptible to particle loss by light induced ejection. Due to the ejections,
planetesimals and smaller bodies will be accelerated or decelerated and drift
outward or inward, respectively. The effect might also explain the entrainment
of dust in dust devils on Mars, especially at high altitudes where gas drag
alone might not be sufficient. | astro-ph_EP |
EPIC247098361b: a transiting warm Saturn on an eccentric $P=11.2$ days
orbit around a $V=9.9$ star: We report the discovery of EPIC247098361b using photometric data of the
Kepler K2 satellite coupled with ground-based spectroscopic observations.
EPIC247098361b has a mass of M$_{P}=0.397\pm 0.037$ M$_J$, a radius of
R$_{P}=1.00 \pm 0.020$ R$_J$, and a moderately low equilibrium temperature of
$T_{eq}=1030 \pm 15$ K due to its relatively large star-planet separation of
$a=0.1036$ AU. EPIC247098361b orbits its bright ($V=9.9$) late F-type host star
in an eccentric orbit ($e=0.258 \pm 0.025$) every 11.2 days, and is one of only
four well characterized warm Jupiters having hosts stars brighter than $V=10$.
We estimate a heavy element content of 20 $\pm$ 7 M$_{\oplus}$ for
EPIC247098361b, which is consistent with standard models of giant planet
formation. The bright host star of EPIC247098361b makes this system a well
suited target for detailed follow-up observations that will aid in the study of
the atmospheres and orbital evolution of giant planets at moderate separations
from their host stars. | astro-ph_EP |
Identification and characterization of the host stars in planetary
microlensing with ELTs: Microlensing offers a unique opportunity to probe exoplanets that are
temperate and beyond the snow line, as small as Jovian satellites, at
extragalactic distance, and even free floating exoplanets, regimes where the
sensitivity of other methods drops dramatically. This is because microlensing
does not depend on the brightness of the planetary host star. The microlensing
method thus provides great leverage in studying the exoplanets beyond the snow
line, posing tests to the core accretion mechanism, especially on the run-away
phase of gas accretion to form giant planets. Here we propose to robustly and
routinely measure the masses of exoplanets beyond 1 AU from their host stars
with the microlensing method; our experiment relies on directly imaging and
resolving the host star (namely the lens) from the background source of the
microlensing events, which requires the high spatial resolution delivered by
the ELTs. A direct result from this project will be planet occurrence rate
beyond the snow line, which will enable us to discern different planet
formation mechanisms. | astro-ph_EP |
Meteorites and the RNA World: A Thermodynamic Model of Nucleobase
Synthesis within Planetesimals: The possible meteorite parent body origin of Earth's pregenetic nucleobases
is substantiated by the guanine (G), adenine (A) and uracil (U) measured in
various meteorites. Cytosine (C) and thymine (T) however are absent in
meteorites, making the emergence of a RNA and later RNA/DNA/protein world
problematic. We investigate the meteorite parent body (planetesimal) origin of
all nucleobases by computationally modeling 18 reactions that potentially
contribute to nucleobase formation in such environments. Out of this list, we
identify the two most important reactions for each nucleobase and find that
these involve small molecules such as HCN, CO, NH3, and water that ultimately
arise from the protoplanetary disks in which planetesimals are built. The
primary result of this study is that cytosine is unlikely to persist within
meteorite parent bodies due to aqueous deamination. Thymine has a
thermodynamically favourable reaction pathway from uracil, formaldehyde and
formic acid, but likely did not persist within planetesimals containing H2O2
due to an oxidation reaction with this molecule. Finally, while FT synthesis is
found to be the dominant source of nucleobases within our model planetesimal,
NC synthesis may still be significant under certain chemical conditions (e.g.
within CR2 parent bodies). We discuss several major consequences of our results
for the origin of the RNA world. | astro-ph_EP |
Multicolor Photometry of Tiny Near-Earth Asteroid 2015 RN$_{35}$ Across
a Wide Range of Phase Angles: Possible Mission Accessible A-type Asteroid: Studying small near-Earth asteroids is important to understand their
dynamical histories and origins as well as to mitigate the damage of the
asteroid impact to the Earth. We report the results of multicolor photometry of
the tiny near-Earth asteroid 2015 RN$_{35}$ using the 3.8 m Seimei telescope in
Japan and the TRAPPIST-South telescope in Chile over 17 nights in 2022 December
and 2023 January. We observed 2015 RN$_{35}$ across a wide range of phase
angles from 2$^{\circ}$ to 30$^{\circ}$ in the $g$, $r$, $i$, and $z$ bands in
the Pan-STARRS system. These lightcurves show that 2015 RN$_{35}$ is in a
non-principal axis spin state with two characteristic periods of $1149.7\pm0.3$
s and $896.01\pm0.01$ s. We found that a slope of a visible spectrum of 2015
RN$_{35}$ is as red as asteroid (269) Justitia, one of the very red objects in
the main belt, which indicates that 2015 RN$_{35}$ can be classified as an A-
or Z-type asteroid. In conjunction with the shallow slope of the phase curve,
we suppose that 2015 RN$_{35}$ is a high-albedo A-type asteroid. We
demonstrated that surface properties of tiny asteroids could be well
constrained by intensive observations across a wide range of phase angles. 2015
RN$_{35}$ is a possible mission accessible A-type near-Earth asteroid with a
small $\Delta v$ of 11.801 km s$^{-1}$ in the launch window between 2030 and
2035. | astro-ph_EP |
On the Method to Infer an Atmosphere on a Tidally-Locked Super Earth
Exoplanet and Upper limits to GJ 876d: We develop a method to infer or rule out the presence of an atmosphere on a
tidally-locked hot super Earth. The question of atmosphere retention is a
fundamental one, especially for planets orbiting M stars due to the star's
long-duration active phase and corresponding potential for stellar-induced
planetary atmospheric escape and erosion. Tidally-locked planets with no
atmosphere are expected to show a Lambertian-like thermal phase curve, causing
the combined light of the planet-star system to vary with planet orbital phase.
We report Spitzer 8 micron IRAC observations of GJ 876 taken over 32
continuous hours and reaching a relative photometric precision of 3.9e-04 per
point for 25.6 s time sampling. This translates to a 3 sigma limit of 5.13e-05
on a planet thermal phase curve amplitude. Despite the almost photon-noise
limited data, we are unable to conclusively infer the presence of an atmosphere
or rule one out on the non-transiting short-period super Earth GJ 876d. The
limiting factor in our observations was the miniscule, monotonic photometric
variation of the slightly active host M star, because the partial sine wave due
to the planet has a component in common with the stellar linear trend. The
proposed method is nevertheless very promising for transiting hot super Earths
with the James Webb Space Telescope and is critical for establishing
observational constraints for atmospheric escape. | astro-ph_EP |
Orbit determination methods for interplanetary missions: development and
use of the Orbit14 software: In the last years, a new generation of interplanetary space missions have
been designed for the exploration of the solar system. At the same time,
radio-science instrumentation has reached an unprecedented level of accuracy,
leading to a significant improvement of our knowledge of celestial bodies.
Along with this hardware upgrade, software products for interplanetary missions
have been greatly refined. In this context, we introduce Orbit14, a precise
orbit determination software developed at the University of Pisa for processing
the radio-science data of the BepiColombo and Juno missions. Along the years,
many tools have been implemented into the software and Orbit14 capitalized the
experience coming from simulations and treatment of real data. In this paper,
we present a review of orbit determination methods developed at the University
of Pisa for radio-science experiments of interplanetary missions. We describe
the basic theory of the process of parameters estimation and refined methods
necessary to have full control on experiments involving spacecraft orbiting
millions of kilometers far from the Earth. Our aim is to give both an extensive
description of the treatment of radio-science experiments and step-to-step
instructions for those who are approaching the field of orbit determination in
the context of space missions. We show also the work conducted on the Juno and
BepiColombo missions by means of the Orbit14 software. In particular, we
summarize the recent results obtained with the gravity experiment of Juno and
the simulations performed so far for the gravimetry-rotation and relativity
experiments of BepiColombo. | astro-ph_EP |
Hints on the origins of particle traps in protoplanetary disks given by
the $M_{\rm{dust}}-M_{\star}$ relation: Demographic surveys of protoplanetary disks, carried out mainly with ALMA,
have provided access to a large range of disk dust masses ($M_{\rm{dust}}$)
around stars with different stellar types and in different star-forming
regions. These surveys found a power-law relation between $M_{\rm{dust}}$ and
$M_{\star}$ that steepens in time, but which is also flatter for transition
disks (TDs). We performed dust evolution models, which included perturbations
to the gas surface density with different amplitudes to investigate the effect
of particle trapping on the $M_{\rm{dust}}-M_{\star}$ relation. These
perturbations were aimed at mimicking pressure bumps that originated from
planets. We focused on the effect caused by different stellar and disk masses
based on exoplanet statistics that demonstrate a dependence of planet mass on
stellar mass and metallicity. Models of dust evolution can reproduce the
observed $M_{\rm{dust}}-M_{\star}$ relation in different star-forming regions
when strong pressure bumps are included and when the disk mass scales with
stellar mass (case of $M_{\rm{disk}}=0.05\,M_\star$ in our models). This result
arises from dust trapping and dust growth beyond centimeter-sized grains inside
pressure bumps. However, the flatter relation of $M_{\rm{dust}}-M_{\star}$ for
TDs and disks with substructures cannot be reproduced by the models unless the
formation of boulders is inhibited inside pressure bumps. In the context of
pressure bumps originating from planets, our results agree with current
exoplanet statistics on giant planet occurrence increasing with stellar mass,
but we cannot draw a conclusion about the type of planets needed in the case of
low-mass stars. This is attributed to the fact that for $M_\star<1\,M_\odot$,
the observed $M_{\rm{dust}}$ obtained from models is very low due to the
efficient growth of dust particles beyond centimeter-sizes inside pressure
bumps. | astro-ph_EP |
Disintegration of Long-Period Comet C/2021 A1 (Leonard): We present imaging observations of the disintegrating long-period comet
C/2021 A1 (Leonard). High resolution observations with Hubble Space Telescope
show no evidence for surviving fragments, and place a 3 sigma upper limit to
their possible radius about 60 m (albedo 0.1 assumed). In contrast, wide field
observations from the Swan Hill Observatory, Australia, show an extensive
debris cloud, the cross-section and estimated mass of which are consistent with
complete disintegration of the nucleus near mid- December 2021 (at about 0.8
au). Two methods give the pre-disruption nucleus radius, r = 0.6+/-0.2 km.
Tidal, collisional, sublimation and pressure-confined explosion models provide
implausible explanations of the disintegration. However, rotational instability
driven by outgassing torques has a very short timescale (of order 0.1 year)
given the orbit and size of the C/2021 A1 nucleus, and offers the most
plausible mechanism for the disruption. Initial rotational breakup is
accelerated by the exposure and strong sublimation of previously buried
volatiles, leading to catastrophic destruction of the nucleus. | astro-ph_EP |
Photophoresis in the circumjovian disk and its impact on the orbital
configuration of the Galilean satellites: Jupiter has four large regular satellites called the Galilean satellites: Io,
Europa, Ganymede, and Callisto. The inner three of the Galilean satellites
orbit in a 4:2:1 mean motion resonance; therefore their orbital configuration
may originate from the stopping of the migration of Io near the bump in the
surface density distribution and following resonant trapping of Europa and
Ganymede. The formation mechanism of the bump near the orbit of the innermost
satellite, Io, is not yet understood, however. Here, we show that photophoresis
in the circumjovian disk could be the cause of the bump, using analytic
calculations of steady-state accretion disks. We propose that photophoresis in
the circumjovian disk could stop the inward migration of dust particles near
the orbit of Io. The resulting dust depleted inner region would have a higher
ionization fraction, and thus admit increased
magnetorotational-instability-driven accretion stress than the outer region.
The increase of the accretion stress at the photophoretic dust barrier would
form a bump in the surface density distribution, halting the migration of Io. | astro-ph_EP |
Obliquities of "Top-Shaped" Asteroids May Not Imply Reshaping by YORP
Spin-up: The timescales over which the YORP effect alters the rotation period and the
obliquity of a small asteroid can be very different, because the corresponding
torques couple to different aspects of the object's shape. For nearly
axisymmetric, "top-shaped" near-Earth asteroids such as 101955 Bennu, spin
timescales are an order of magnitude or more longer than obliquity timescales,
which are of order 10^5 to 10^6 yr. The observed low obliquities (near 0 or 180
degrees) of top-shaped asteroids do not constitute evidence that they acquired
their present shapes and spins through YORP spin-up, because low obliquities
are expected regardless of the spin-up or reshaping mechanism. | astro-ph_EP |
Probable Spin-Orbit Aligned Super-Earth Planet Candidate KOI-2138.01: We use rotational gravity darkening in the disk of \emph{Kepler} star
KOI-2138 to show that the orbit of $2.1-R_\oplus$ transiting planet candidate
KOI-2138.01 has a low projected spin-orbit alignment of $\lambda=1^\circ\pm13$.
KOI-2138.01 is just the second super-Earth with a measured spin-orbit alignment
after 55 Cancri e, and the first to be aligned. With a 23.55-day orbital
period, KOI-2138.01 may represent the tip of a future iceberg of
solar-system-like terrestrial planets having intermediate periods and
low-inclination circular orbits. | astro-ph_EP |
Interplanetary Laser Tri-lateration Network: simulation with INPOP
planetary ephemerides: This study is done in the context of the project titled Interplanetary Laser
Tri-lateration Network (ILTN) proposed by \cite{2018P&SS..153..127S} and
investigated more in details by \cite{2022P&SS..21405415B} and
\cite{2022P&SS..21505423B}. The original idea was to propose interplanetary
measurements (in this case between Venus, Mars and the earth) as a way to
measure the solar system expansion. But some recent interests on the
measurement of asteroid masses and more generally the study of the mass
distribution in the outer solar system appear with the ILTN. In this work, we
are investigating how different possible configurations of interplanetary
measurements of distances can be introduced in planetary ephemeris construction
and how they improve our knowledge of planet orbits and other related
parameters. | astro-ph_EP |
Microlensed Radio Emission from Exoplanets: In this paper, we investigate the detectability of radio emission from
exoplanets, especially hot Jupiters, which are magnified by gravitational
microlensing. Because hot Jupiters have orbital periods much shorter than the
characteristic timescale of microlensing, the magnification curve has a unique
wavy feature depending on the orbital parameters. This feature is useful to
identify radio emission from exoplanets and, in addition to magnification,
makes it easier to detect exoplanets directly. We also estimate the expected
event rate red of the detectable level of microlensed planetary radio
emissions, assuming the LOFAR and the first phase of the Square Kilometre
Array. | astro-ph_EP |
Earth as an Exoplanet. III. Using Empirical Thermal Emission Spectra as
Input for Atmospheric Retrieval of an Earth-Twin Exoplanet: In this study, we treat Earth as an exoplanet and investigate our home planet
by means of a potential future mid-infrared (MIR) space mission called the
Large Interferometer For Exoplanets (LIFE). We combine thermal spectra from an
empirical dataset of disk-integrated Earth observations with a noise model for
LIFE to create mock observations. We apply a state-of-the-art atmospheric
retrieval framework to characterize the planet, assess the potential for
detecting the known bioindicators, and investigate the impact of viewing
geometry, seasonality, and patchy clouds on the characterization. Key findings
include: (1) we are observing a temperate habitable planet with significant
abundances of $\mathrm{CO_2}$, $\mathrm{H_2O}$, $\mathrm{O_3}$, and
$\mathrm{CH_4}$; (2) seasonal variations in the surface and equilibrium
temperature, and in the Bond albedo are detectable; (3) the viewing geometry
and the spatially and temporally unresolved nature of our observations only
have a minor impact on the characterization; (4) Earth's variable H2O profile
and patchy cloud coverage lead to biased retrieval results for the atmospheric
structure and trace gas abundances; (5) the limited extent of Earth's seasonal
variations in biosignature abundances makes the direct detection of its
biosphere through atmospheric seasonality unlikely. Our results suggest that
LIFE could correctly identify Earth as a planet where life could thrive, with
detectable levels of bioindicators, a temperate climate, and surface conditions
allowing liquid surface water. Even if atmospheric seasonality is not easily
observed, our study demonstrates that next generation, optimized space missions
can assess whether nearby temperate terrestrial exoplanets are habitable or
even inhabited. | astro-ph_EP |
A Potential Aid in the Target Selection for the Comet Interceptor
Mission: The upcoming Comet Interceptor mission involves a parking phase around the
Sun-Earth L2 point before transferring to intercept the orbit of a long period
comet, interstellar object or a back-up target in the form of a short-period
comet. The target is not certain to be known before the launch in 2029. During
the parking phase there may thus arise a scenario wherein a decision needs to
be taken of whether to go for a particular comet or whether to discard that
option in the hope that a better target will appear within a reasonable time
frame later on. We present an expectation value-based formalism that could aid
in the associated decision making provided that outlined requirements for its
implementation exist. | astro-ph_EP |
Reduced atmospheres of post-impact worlds: The early Earth: Impacts may have had a significant effect on the atmospheric chemistry of the
early Earth. Reduced phases in the impactor (e.g., metallic iron) can reduce
the planet's H$_2$O inventory to produce massive atmospheres rich in H$_2$.
Whilst previous studies have focused on the interactions between the impactor
and atmosphere in such scenarios, we investigate two further effects, 1) the
distribution of the impactor's iron inventory during impact between the target
interior, target atmosphere, and escaping the target, and 2) interactions
between the post-impact atmosphere and the impact-generated melt phase. We find
that these two effects can potentially counterbalance each other, with the
melt-atmosphere interactions acting to restore reducing power to the atmosphere
that was initially accreted by the melt phase. For a $\sim10^{22}\,\mathrm{kg}$
impactor, when the iron accreted by the melt phase is fully available to reduce
this melt, we find an equilibrium atmosphere with H$_2$ column density
$\sim10^4\,\mathrm{moles\,cm^{-2}}$
($p\mathrm{H2}\sim120\,\mathrm{bars}\mathrm{,}~X_\mathrm{H2}\sim0.77$),
consistent with previous estimates. However, when the iron is not available to
reduce the melt (e.g., sinking out in large diameter blobs), we find
significantly less H$_2$ ($7\times10^2-5\times10^3\,\mathrm{moles\,cm^{-2}}$,
$p\mathrm{H2}\lesssim60\,\mathrm{bars}\mathrm{,}~X_\mathrm{H2}\lesssim0.41$).
These lower H$_2$ abundances are sufficiently high that species important to
prebiotic chemistry can form (e.g., NH3, HCN), but sufficiently low that the
greenhouse heating effects associated with highly reducing atmospheres, which
are problematic to such chemistry, are suppressed. The manner in which iron is
accreted by the impact-generated melt phase is critical in determining the
reducing power of the atmosphere and re-solidified melt pool in the aftermath
of impact. | astro-ph_EP |
Composition of Terrestrial Exoplanet Atmospheres from Meteorite
Outgassing Experiments: Terrestrial exoplanets likely form initial atmospheres through outgassing
during and after accretion, although there is currently no first-principles
understanding of how to connect a planet's bulk composition to its early
atmospheric properties. Important insights into this connection can be gained
by assaying meteorites, representative samples of planetary building blocks. We
perform laboratory outgassing experiments that use a mass spectrometer to
measure the abundances of volatiles released when meteorite samples are heated
to 1200 $^{\circ}$C. We find that outgassing from three carbonaceous chondrite
samples consistently produce H$_2$O-rich (averaged ~66 %) atmospheres but with
significant amounts of CO (~18 %) and CO$_2$ (~15 %) as well as smaller
quantities of H$_2$ and H$_2$S (up to 1 %). These results provide experimental
constraints on the initial chemical composition in theoretical models of
terrestrial planet atmospheres, supplying abundances for principal gas species
as a function of temperature. | astro-ph_EP |
Is there a background population of high-albedo objects in
geosynchronous orbits around Earth?: Old, digitized astronomical images taken before the human spacefaring age
offer a unique view of the sky devoid of known artificial satellites. In this
paper, we have carried out the first optical searches ever for non-terrestrial
artifacts near the Earth following the method proposed in Villarroel et al.
(2022). We use images contained in the First Palomar Sky Survey to search for
simultaneous (during a plate exposure time) transients that in addition to
being point-like, are aligned. We provide a shortlist of the most promising
candidates of aligned transients, that must be examined with the help of a
microscope to separate celestial sources from plate defects with coincidentally
star-like brightness profiles. We further explore one possible, but not unique,
interpretation in terms of fast reflections off high-albedo objects in
geosynchronous orbits around Earth. If a future study rules out each multiple
transient candidate, the estimated surface density becomes an upper limit of
$<10^{-9}$ objects km$^{-2}$ non-terrestrial artifacts in geosynchronous orbits
around Earth. Finally, we conclude that observations and analysis of multiple,
simultaneously appearing and vanishing light sources on the sky merit serious
further attention, regardless of their origin. | astro-ph_EP |
Short-term variability on the surface of (1) Ceres. A changing amount of
water ice?: Context: The dwarf planet (1) Ceres - next target of the NASA Dawn mission -
is the largest body in the asteroid main belt; although several observations of
this body have been performed so far, the presence of surface water ice is
still questioned.
Aims: Our goal is to better understand the surface composition of Ceres, and
to constrain the presence of exposed water ice.
Methods: We acquired new visible and near-infrared spectra at the Telescopio
Nazionale Galileo (TNG, La Palma, Spain), and reanalyzed literature spectra in
the 3-$\mu$m region.
Results: We obtained the first rotationally-resolved spectroscopic
observations of Ceres at visible wavelengths. Visible spectra taken one month
apart at almost the same planetocentric coordinates show a significant slope
variation (up to 3 %/10$^3\AA$). A faint absorption centered at 0.67 $\mu$m,
possibly due to aqueous alteration, is detected in a subset of our spectra. The
various explanations in the literature for the 3.06-$\mu$m feature can be
interpreted as due to a variable amount of surface water ice at different
epochs.
Conclusions: The remarkable short-term temporal variability of the visible
spectral slope, and the changing shape of the 3.06-$\mu$m band, can be hints of
different amounts of water ice exposed on the surface of Ceres. This would be
in agreement with the recent detection by the Herschel Space Observatory of
localized and transient sources of water vapour over this dwarf planet. | astro-ph_EP |
Spin Evolution and Cometary Interpretation of the Interstellar Minor
Object 1I/2017 'Oumuamua: Observations of the first interstellar minor object 1I/2017 'Oumuamua did not
reveal direct signs of outgassing that would have been natural if it had
volatile-rich composition. However, a recent measurement by Micheli et al
(2018) of a substantial non-gravitational acceleration affecting the orbit of
this object has been interpreted as resulting from its cometary activity, which
must be rather vigorous. Here we critically re-assess this interpretation by
exploring the implications of measured non-gravitational acceleration for the
'Oumuamua's rotational state. We show that outgassing torques should drive
rapid evolution of 'Oumuamua's spin (on a timescale of a few days), assuming
torque asymmetry typical for the Solar System comets. However, given the highly
elongated shape of the object, its torque asymmetry is likely higher, implying
even faster evolution. This would have resulted in rapid rotational fission of
'Oumuamua during its journey through the Solar System and is clearly
incompatible with the relative stability of its rotational state inferred from
photometric variability. Based on these arguments, as well as the lack of
direct signs of outgassing, we conclude that the classification of 'Oumuamua as
a comet (invoked to explain its claimed anomalous acceleration) is
questionable. | astro-ph_EP |
Probing the inner boundaries of Saturn's A ring with the Iapetus -1:0
nodal bending wave: The Iapetus -1:0 nodal bending wave, the first spiral wave ever described in
Saturn's rings, has been seen again for the first time in 29 years. We
demonstrate that it is in fact the nodal bending wave, not the 1:0 apsidal
density wave as previously reported. We use wavelet analysis to determine the
wavelength profile, thus deriving the surface density at every point in the
region covered by the bending wave. This profile is consistent with surface
densities measured from more localized spiral density waves in the outer
Cassini Division and the inner and mid-A Ring, varying smoothly from the low
values of the former to the higher values of the latter.
Most remarkably, our analysis indicates that there is no significant change
in surface density across the boundary between the outer Cassini Division and
the inner-A ring, despite the very abrupt increase in optical depth and
reflected brightness at this location. We consider anew the nature of the
classically identified "inner edge of the A ring," given that it does not
appear to be correlated with any abrupt increase in surface density. There is
an abrupt increase in surface density at the Pandora 5:4 density wave, ~300 km
outward of the A ring's inner edge. Further study is needed to robustly
interpret our findings in terms of particle properties and abundances, much
less to explain the origins of the implied structure. | astro-ph_EP |
The International Deep Planet Survey II: The frequency of directly
imaged giant exoplanets with stellar mass: Radial velocity and transit methods are effective for the study of short
orbital period exoplanets but they hardly probe objects at large separations
for which direct imaging can be used. We carried out the international deep
planet survey of 292 young nearby stars to search for giant exoplanets and
determine their frequency. We developed a pipeline for a uniform processing of
all the data that we have recorded with NIRC2/Keck II, NIRI/Gemini North,
NICI/Gemini South, and NACO/VLT for 14 years. The pipeline first applies
cosmetic corrections and then reduces the speckle intensity to enhance the
contrast in the images. The main result of the international deep planet survey
is the discovery of the HR 8799 exoplanets. We also detected 59 visual multiple
systems including 16 new binary stars and 2 new triple stellar systems, as well
as 2,279 point-like sources. We used Monte Carlo simulations and the Bayesian
theorem to determine that 1.05[+2.80-0.70]% of stars harbor at least one giant
planet between 0.5 and 14M_J and between 20 and 300 AU. This result is obtained
assuming uniform distributions of planet masses and semi-major axes. If we
consider power law distributions as measured for close-in planets instead, the
derived frequency is 2.30[+5.95-1.55]%, recalling the strong impact of
assumptions on Monte Carlo output distributions. We also find no evidence that
the derived frequency depends on the mass of the hosting star, whereas it does
for close-in planets. The international deep planet survey provides a database
of confirmed background sources that may be useful for other exoplanet direct
imaging surveys. It also puts new constraints on the number of stars with at
least one giant planet reducing by a factor of two the frequencies derived by
almost all previous works. | astro-ph_EP |
Modeling of the zodiacal emission for the AKARI/IRC mid-infrared all-sky
diffuse maps: The zodiacal emission, which is the thermal infrared (IR) emission from the
interplanetary dust (IPD) in our Solar System, has been studied for a long
time. Nevertheless, accurate modeling of the zodiacal emission has not been
successful to reproduce the all-sky spatial distribution of the zodiacal
emission, especially in the mid-IR where the zodiacal emission peaks. We
therefore aim to improve the IPD cloud model based on Kelsall et al. 1998,
using the AKARI 9 and 18 micron all-sky diffuse maps. By adopting a new fitting
method based on the total brightness, we have succeeded in reducing the
residual levels after subtraction of the zodiacal emission from the AKARI data
and thus in improving the modeling of the zodiacal emission. Comparing the
AKARI and the COBE data, we confirm that the changes from the previous model to
our new model are mostly due to model improvements, but not temporal variations
between the AKARI and the COBE epoch, except for the position of the
Earth-trailing blob. Our results suggest that the size of the smooth cloud, a
dominant component in the model, is by about 10% more compact than previously
thought, and that the dust sizes are not large enough to emit blackbody
radiation in the mid-IR. Furthermore we significantly detect an
isotropically-distributed IPD component, owing to accurate baseline measurement
with AKARI. | astro-ph_EP |
The 8 Micron Phase Variation of the Hot Saturn HD 149026b: We monitor the star HD 149026 and its Saturn-mass planet at 8.0 micron over
slightly more than half an orbit using the Infrared Array Camera (IRAC) on the
Spitzer Space Telescope. We find an increase of 0.0227% +/- 0.0066% (3.4 sigma
significance) in the combined planet-star flux during this interval. The
minimum flux from the planet is 45% +/- 19% of the maximum planet flux,
corresponding to a difference in brightness temperature of 480 +/- 140 K
between the two hemispheres. We derive a new secondary eclipse depth of 0.0411%
+/- 0.0076% in this band, corresponding to a dayside brightness temperature of
1440 +/- 150 K. Our new secondary eclipse depth is half that of a previous
measurement (3.0 sigma difference) in this same bandpass by Harrington et al.
(2007). We re-fit the Harrington et al. (2007) data and obtain a comparably
good fit with a smaller eclipse depth that is consistent with our new value. In
contrast to earlier claims, our new eclipse depth suggests that this planet's
dayside emission spectrum is relatively cool, with an 8 micron brightness
temperature that is less than the maximum planet-wide equilibrium temperature.
We measure the interval between the transit and secondary eclipse and find that
that the secondary eclipse occurs 20.9 +7.2 / -6.5 minutes earlier (2.9 sigma)
than predicted for a circular orbit, a marginally significant result. This
corresponds to e*cos(omega) = -0.0079 +0.0027 / -0.0025 where e is the planet's
orbital eccentricity and omega is the argument of pericenter. | astro-ph_EP |
VUV-absorption cross section of carbon dioxide from 150 to 800 K and
applications to warm exoplanetary atmospheres: Most exoplanets detected so far have atmospheric T significantly higher than
300K. Often close to their star, they receive an intense UV photons flux that
triggers important photodissociation processes. The T dependency of VUV
absorption cross sections are poorly known, leading to an undefined uncertainty
in atmospheric models. Similarly, data measured at low T similar to that of the
high atmosphere of Mars, Venus, and Titan are often lacking. Our aim is to
quantify the T dependency of the abs. cross section of important molecules in
planetary atmospheres. We want to provide both high-resolution data at T
prevailing in these media and a simple parameterization of the absorption in
order to simplify its use in photochemical models. This study focuses on carbon
dioxide. We performed experimental measurements of CO$_2$ absorption cross
section with synchrotron radiation for the wavelength range (115--200nm). For
longer wavelengths (195--230nm), we used a deuterium lamp and a 1.5m Jobin-Yvon
spectrometer. We used these data in our 1D thermo-photochemical model in order
to study their impact on the predicted atmospheric compositions. The cross
section of CO$_2$ increases with T. It can be separated in two parts: a
continuum and a fine structure superimposed on the continuum. The variation of
the continuum of absorption can be represented by the sum of three gaussian
functions. Using data at high T in thermo-photochemical models modifies
significantly the abundance and the photodissociation rates of many species, in
addition to CO$_2$, such as methane and ammonia. These deviations have an
impact on synthetic transmission spectra, leading to variations of up to 5 ppm.
We present a full set of HR ($\Delta \lambda$=0.03nm) absorption cross sections
of CO$_2$ from 115 to 230nm for T ranging from 150 to 800K. | astro-ph_EP |
Saturn Ring Seismology: Evidence for Stable Stratification in the Deep
Interior of Saturn: Seismology allows for direct observational constraints on the interior
structures of stars and planets. Recent observations of Saturn's ring system
have revealed the presence of density waves within the rings excited by
oscillation modes within Saturn, allowing for precise measurements of a limited
set of the planet's mode frequencies. We construct interior structure models of
Saturn, compute the corresponding mode frequencies, and compare them with the
observed mode frequencies. The fundamental mode frequencies of our models match
the observed frequencies (of the largest amplitude waves) to an accuracy of
$\sim 1 \%$, confirming that these waves are indeed excited by Saturn's
f-modes. The presence of the lower amplitude waves (finely split in frequency
from the f-modes) can only be reproduced in models containing gravity modes
that propagate in a stably stratified region of the planet. The stable
stratification must exist deep within the planet near the large density
gradients between the core and envelope. Our models cannot easily reproduce the
observed fine splitting of the $m=-3$ modes, suggesting that additional effects
(e.g., significant latitudinal differential rotation) may be important. | astro-ph_EP |
Uranus at equinox: Cloud morphology and dynamics: As the 7 December 2007 equinox of Uranus approached, ring and atmosphere
observers produced a substantial collection of observations using the 10-m Keck
telescope and the Hubble Space Telescope. Those spanning the period from 7 June
2007 through 9 September 2007 we used to identify and track cloud features,
determine atmospheric motions, characterize cloud morphology and dynamics, and
define changes in atmospheric band structure. We confirmed the existence of the
suspected northern hemisphere prograde jet, locating its peak near 58 N, and
extended wind speed measurements to 73 N. For 28 cloud features we obtained
extremely high wind-speed accuracy through extended tracking times. The new
results confirm a small N-S asymmetry in the zonal wind profile, and the lack
of any change in the southern hemisphere between 1986 (near solstice) and 2007
(near equinox) suggests that the asymmetry may be permanent rather than
seasonally reversing. In the 2007 images we found two prominent groups of
discrete cloud features with very long lifetimes. The one near 30 S has
departed from its previous oscillatory motion and started a significant
northward drift, accompanied by substantial morphological changes. The complex
of features near 30 N remained at a nearly fixed latitude, while exhibiting
some characteristics of a dark spot accompanied by bright companion features.
Smaller and less stable features were used to track cloud motions at other
latitudes, some of which lasted over many planet rotations, though many could
not be tracked beyond a single transit. A bright band has developed near 45 N,
while the bright band near 45 S has begun to decline, both events in agreement
with the idea that the asymmetric band structure of Uranus is a delayed
response to solar forcing, but with a surprisingly short delay of only a few
years. | astro-ph_EP |
Constraining the oblateness of transiting planets with photometry and
spectroscopy: Rapid planetary rotation can cause the equilibrium shape of a planet to be
oblate. While planetary oblateness has mostly been probed by examining the
subtle ingress and egress features in photometric transit light curves, we
investigate the effect of oblateness on the spectroscopic Rossiter-McLaughlin
(RM) signals. We found that a giant planet, with planet-to-star radius ratio of
0.15 and Saturn-like oblateness of 0.098, can cause spectroscopic signatures
with amplitudes up to 1.1 ms$^{-1}$ which is detectable by high-precision
spectrographs such as ESPRESSO. We also found that the spectroscopic oblateness
signals are particularly amplified for transits across rapidly rotating stars
and for planets with spin-orbit misalignment thereby making them more prominent
than the photometric signals at some transit orientations. We compared the
detectability of oblateness in photometry and spectroscopy and found that
photometric light curves are more sensitive to detecting oblateness than the
spectroscopic RM signals mostly because they can be sampled with higher cadence
to better probe the oblateness ingress and egress anomaly. However, joint
analyses of the light curve and RM signal of a transiting planet provides more
accurate and precise estimate of the planet's oblateness. Therefore, ESPRESSO
alongside ongoing and upcoming photometric instruments such as TESS, CHEOPS,
PLATO and JWST will be extremely useful in measuring planet oblateness. | astro-ph_EP |
The Dynamics of Co-orbital Giant Exomoons -- Applications for the
Kepler-1625 b and Kepler-1708 b Satellite Systems: Exomoons are a missing piece of exoplanetary science. Recently, two promising
candidates were proposed, Kepler-1625 b-I and Kepler-1708 b-I. While the latter
still lacks a dynamical analysis of its stability, Kepler-1625 b-I has already
been the subject of several studies regarding its stability and origin.
Moreover, previous works have shown that this satellite system could harbour at
least two stable massive moons. Motivated by these results, we explored the
stability of co-orbital exomoons using the candidates Kepler-1625 b-I and
Kepler-1708 b-I as case studies. To do so, we performed numerical simulations
of systems composed of the star, planet, and the co-orbital pair formed by the
proposed candidates and another massive body. For the additional satellite, we
varied its mass and size from a Mars-like to the case where both satellites
have the same physical characteristics. We investigated the co-orbital region
around the Lagrangian equilibrium point $L_4$ of the system, setting the
orbital separation between the satellites from $\theta_{min} = 30^{\circ}$ to
$\theta_{max} = 90^{\circ}$. Our results show that stability islands are
possible in the co-orbital region of Kepler-1708 b-I as a function of the
co-orbital companion's mass and angular separation. Also, we identified that
resonances of librational frequencies, especially the 2:1 resonance, can
constrain the mass of the co-orbital companion. On the other hand, we found
that the proximity between the host planet and the star makes the co-orbital
region around Kepler-1625 b-I unstable for a massive companion. Finally, we
provide TTV profiles for a planet orbited by co-orbital exomoons. | astro-ph_EP |
Desorption Kinetics and Binding Energies of Small Hydrocarbons: Small hydrocarbons are an important organic reservoir in protostellar and
protoplanetary environments. Constraints on desorption temperatures and binding
energies of such hydrocarbons are needed for accurate predictions of where
these molecules exist in the ice vs. gas-phase during the different stages of
star and planet formation. Through a series of temperature programmed
desorption (TPD) experiments, we constrain the binding energies of 2 and
3-carbon hydrocarbons (C$_{2}$H$_{2}$ - acetylene, C$_{2}$H$_{4}$ - ethylene,
C$_{2}$H$_{6}$ - ethane, C$_{3}$H$_{4}$ - propyne, C$_{3}$H$_{6}$ - propene,
and C$_{3}$H$_{8}$ - propane) to 2200-4200 K in the case of pure amorphous
ices, to 2400-4400 K on compact amorphous H$_{2}$O, and to 2800-4700 K on
porous amorphous H$_{2}$O. The 3-carbon hydrocarbon binding energies are always
larger than the 2-carbon hydrocarbon binding energies. Within the 2- and
3-carbon hydrocarbon families, the alkynes (i.e., least-saturated) hydrocarbons
exhibit the largest binding energies, while the alkane and alkene binding
energies are comparable. Binding energies are $\sim$5-20% higher on water ice
substrates compared to pure ices, which is a small increase compared to what
has been measured for other volatile molecules such as CO and N$_{2}$. Thus in
the case of hydrocarbons, H$_{2}$O has a less pronounced effect on sublimation
front locations (i.e., snowlines) in protoplanetary disks. | 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 |
Lie-series for orbital elements -- I. The planar case: Lie-integration is one of the most efficient algorithms for numerical
integration of ordinary differential equations if high precision is needed for
longer terms. The method is based on the computation of the Taylor-coefficients
of the solution as a set of recurrence relations. In this paper we present
these recurrence formulae for orbital elements and other integrals of motion
for the planar $N$-body problem. We show that if the reference frame is fixed
to one of the bodies -- for instance to the Sun in the case of the Solar System
--, the higher order coefficients for all orbital elements and integrals of
motion depend only on the mutual terms corresponding to the orbiting bodies. | astro-ph_EP |
Radial Velocity Discovery of an Eccentric Jovian World Orbiting at 18 au: Based on two decades of radial velocity (RV) observations using Keck/HIRES
and McDonald/Tull, and more recent observations using the Automated Planet
Finder, we found that the nearby star HR 5183 (HD 120066) hosts a 3$M_J$
minimum mass planet with an orbital period of $74^{+43}_{-22}$ years. The orbit
is highly eccentric (e$\simeq$0.84), shuttling the planet from within the orbit
of Jupiter to beyond the orbit of Neptune. Our careful survey design enabled
high cadence observations before, during, and after the planet's periastron
passage, yielding precise orbital parameter constraints. We searched for
stellar or planetary companions that could have excited the planet's
eccentricity, but found no candidates, potentially implying that the perturber
was ejected from the system. We did identify a bound stellar companion more
than 15,000 au from the primary, but reasoned that it is currently too widely
separated to have an appreciable effect on HR 5183 b. Because HR 5183 b's wide
orbit takes it more than 30 au (1") from its star, we also explored the
potential of complimentary studies with direct imaging or stellar astrometry.
We found that a Gaia detection is very likely, and that imaging at 10 $\mu$m is
a promising avenue. This discovery highlights the value of long-baseline RV
surveys for discovering and characterizing long-period, eccentric Jovian
planets. This population may offer important insights into the dynamical
evolution of planetary systems containing multiple massive planets. | astro-ph_EP |
Galactic tide and secular orbital evolution: Equation of motion for the galactic tide is treated for the case of a comet
situated in the Oort cloud of comets. We take into account that galactic
potential and mass density depend on a distance from the galactic equator and
on a distance from the rotational axis of the Galaxy. Secular evolution of
orbital elements is presented. New terms generated by the Sun's oscillation
about the galactic plane are considered. The inclusion of the new terms into
the equation of motion of the comet leads to orbital evolution which may be
significantly different from the conventional approach. The usage of the
secular time derivatives is limited to the cases when orbital period of the
comet is much less than i) the period of oscillations of the Sun around the
galactic equator, and, ii) the orbital period of the motion of the Sun around
the galactic center. | astro-ph_EP |
Mony a Mickle Maks a Muckle: Minor Body Observations with Optical
Telescopes of All Sizes: I review the current capabilities of small, medium and large telescopes in
the study of minor bodies of the Solar System (MBOSS), with the goal of
identifying those areas where the next generation of Extremely Large Telescopes
(ELTs) are required to progress. This also leads to a discussion of the
synergies between large and small telescopes. It is clear that the new
facilities that will become available in the next decades will allow us to
discover smaller and more distant objects (completing size distributions) and
to characterise and even resolve larger individual bodies and multiple systems,
however we must also recognise that there is still much to be learned from wide
surveys that require more time on more telescopes than can ever be available on
ELTs. Smaller telescopes are still required to discover and characterise large
samples of MBOSS. | 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 |
Andrade rheology in time-domain. Application to Enceladus' dissipation
of energy due to forced libration: The main purpose of this work is to present a time-domain implementation of
the Andrade rheology, instead of the traditional expansion in terms of a
Fourier series of the tidal potential. This approach can be used in any fully
three dimensional numerical simulation of the dynamics of a system of many
deformable bodies. In particular, it allows large eccentricities, large mutual
inclinations, and it is not limited to quasi-periodic perturbations. It can
take into account an extended class of perturbations, such as chaotic motions,
transient events, and resonant librations.
The results are presented by means of a concrete application: the analysis of
the libration of Enceladus. This is done by means of both analytic formulas in
the frequency domain and direct numerical simulations. We do not a priori
assume that Enceladus has a triaxial shape, the eventual triaxiality is a
consequence of the satellite motion and its rheology. As a result we obtain an
analytic formula for the amplitude of libration that incorporates a new
correction due to the rheology.
Our results provide an estimation of the amplitude of libration of the core
of Enceladus as 0.6% of that of the shell. They also reproduce the observed 10
GW of tidal heat generated by Enceladus with a value of $0.17\times
10^{14}$Pa$\cdot$s for the global effective viscosity under both Maxwell and
Andrade rheology. | astro-ph_EP |
Understanding the Planetary Formation and Evolution in Star
Clusters(UPiC)-I: Evidence of Hot Giant Exoplanets Formation Timescales: Planets in young star clusters could shed light on planet formation and
evolution since star clusters can provide accurate age estimation. However, the
number of transiting planets detected in clusters was only $\sim 30$, too small
for statistical analysis. Thanks to the unprecedented high-precision
astrometric data provided by Gaia DR2 and Gaia DR3, many new Open Clusters(OCs)
and comoving groups have been identified. The UPiC project aims to find
observational evidence and interpret how planet form and evolve in cluster
environments. In this work, we cross-match the stellar catalogs of new OCs and
comoving groups with confirmed planets and candidates. We carefully remove
false positives and obtain the biggest catalog of planets in star clusters up
to now, which consists of 73 confirmed planets and 84 planet candidates. After
age validation, we obtain the radius--age diagram of these planets/candidates.
We find an increment of the fraction of Hot Jupiters(HJs) around 100 Myr and
attribute the increment to the flyby-induced high-e migration in star clusters.
An additional small bump of the fraction of HJs after 1 Gyr is detected, which
indicates the formation timescale of HJ around field stars is much larger than
that in star clusters. Thus, stellar environments play important roles in the
formation of HJs. The hot-Neptune desert occurs around 100 Myr in our sample. A
combination of photoevaporation and high-e migration may sculpt the hot-Neptune
desert in clusters. | astro-ph_EP |
A Survey of CO, CO2, and H2O in Comets and Centaurs: CO and CO$_2$ are the two dominant carbon-bearing molecules in comae and have
major roles in driving activity. Their relative abundances also provide strong
observational constraints to models of solar system formation and evolution but
have never been studied together in a large sample of comets. We carefully
compiled and analyzed published measurements of simultaneous CO and CO$_2$
production rates for 25 comets. Approximately half of the comae have
substantially more CO$_2$ than CO, about a third are CO-dominated and about a
tenth produce a comparable amount of both. There may be a heliocentric
dependence to this ratio with CO dominating comae beyond 3.5 au. Eight out of
nine of the Jupiter Family Comets in our study produce more CO$_2$ than CO. The
six dynamically new comets produce more CO$_2$ relative to CO than the eight
Oort Cloud comets that have made multiple passes through the inner solar
system. This may be explained by long-term cosmic ray processing of a comet
nucleus's outer layers. We find (Q$_{CO}$/Q$_{H_2O}$)$_{median}$ = 3 $\pm$ 1\%
and (Q$_{CO_2}$/Q$_{H_2O}$)$_{median}$ = 12 $\pm$ 2\%. The inorganic volatile
carbon budget was estimated to be Q$_{CO}$+Q$_{CO_2}$)/Q$_{H_2O}$ $\sim$ 18\%
for most comets. Between 0.7 to 4.6 au, CO$_2$ outgassing appears to be more
intimately tied to the water production in a way that the CO is not. The
volatile carbon/oxygen ratio for 18 comets is C/O$_{median}$ $\sim$ 13\%, which
is consistent with a comet formation environment that is well within the CO
snow line. | astro-ph_EP |
The PHOENIX Exoplanet Retrieval Algorithm and Using H$^{-}$ Opacity as a
Probe in Ultra-hot Jupiters: Atmospheric retrievals are now a standard tool to analyze observations of
exoplanet atmospheres. This data-driven approach quantitatively compares
atmospheric models to observations in order to estimate atmospheric properties
and their uncertainties. In this paper, we introduce a new retrieval package,
the PHOENIX Exoplanet Retrieval Analysis (PETRA). PETRA places the PHOENIX
atmosphere model in a retrieval framework, allowing us to combine the strengths
of a well-tested and widely-used atmosphere model with the advantages of
retrieval algorithms. We validate PETRA by retrieving on simulated data for
which the true atmospheric state is known. We also show that PETRA can
successfully reproduce results from previously published retrievals of WASP-43b
and HD 209458b. For the WASP-43b results, we show the effect that different
line lists and line profile treatments have on the retrieved atmospheric
properties. Lastly, we describe a novel technique for retrieving the
temperature structure and $e^{-}$ density in ultra-hot Jupiters using H$^{-}$
opacity, allowing us to probe atmospheres devoid of most molecular features
with JWST. | astro-ph_EP |
Effect of near-earth thunderstorms electric field on the intensity of
ground cosmic ray positrons/electrons in Tibet: Monte Carlo simulations are performed to study the correlation between the
ground cosmic ray intensity and near-earth thunderstorms electric field at YBJ
(4300 m a.s.l., Tibet, China). The variations of the secondary cosmic ray
intensity are found to be highly dependent on the strength and polarity of the
electric field. In negative fields and in positive fields greater than 600
V/cm, the total number of ground comic ray positrons and electrons increases
with increasing electric field strength. And these values increase more
obviously when involving a shower with lower primary energy or a higher zenith
angle. While in positive fields ranging from 0 to 600 V/cm, the total number of
ground comic ray positrons and electrons declines and the amplitude is up to
3.1% for vertical showers. A decrease of intensity occurs for inclined showers
in positive fields less than 500 V/cm, which is accompanied by smaller
amplitudes. In this paper, the intensity changes are discussed, especially
concerning the decreases in positive electric fields. Our simulation results
are in good agreement with ground-based experimental results obtained from
ARGO-YBJ and the Carpet air shower array. These results could be helpful in
understanding the acceleration mechanisms of secondary charged particles caused
by an atmospheric electric field. | astro-ph_EP |
ALMA Images the Eccentric HD 53143 Debris Disk: We present ALMA 1.3 mm observations of the HD~53143 debris disk - the first
infrared or millimeter image produced of this ~1 Gyr-old solar-analogue.
Previous HST STIS coronagraphic imaging did not detect flux along the minor
axis of the disk which could suggest a face-on geometry with two 'clumps' of
dust. These ALMA observations reveal a disk with a strikingly different
structure. In order to fit models to the millimeter visibilities and constrain
the uncertainties on the disk parameters, we adopt an MCMC approach. This is
the most eccentric debris disk observed to date with a forced eccentricity of
$0.21\pm0.02$, nearly twice that of the Fomalhaut debris disk, and also
displays apocenter glow. Although this eccentric model fits the outer debris
disk well, there are significant interior residuals remaining that may suggest
a possible edge-on inner disk, which remains unresolved in these observations.
Combined with the observed structure difference between HST and ALMA, these
results suggest a potential previous scattering event or dynamical instability
in this system. We also note that the stellar flux changes considerably over
the course of our observations, suggesting flaring at millimeter wavelengths.
Using simultaneous TESS observations, we determine the stellar rotation period
to be $9.6\pm0.1$ days. | astro-ph_EP |
Two Strengths of Ordinary Chondritic Meteoroids as Derived from their
Atmospheric Fragmentation Modeling: The internal structure and strength of small asteroids and large meteoroids
is poorly known. Observation of bright fireballs in the Earth's atmosphere can
prospect meteoroid structure by studying meteoroid fragmentation during the
flight. Earlier evaluations showed that meteoroid strength is significantly
lower than that of the recovered meteorites. We present detailed study of
atmospheric fragmentation of seven meteorite falls, all ordinary chondrites,
and 14 other fireballs, where meteorite fall was predicted but the meteorites,
probably also ordinary chondrites, were not recovered. All observations were
made by the autonomous observatories of the European Fireball Network and
include detailed radiometric light curves. A model, called the semi-empirical
fragmentation model, was developed to fit the light curves and decelerations.
Videos showing individual fragments were available in some cases. The results
demonstrated that meteoroids do not fragment randomly but in two distinct
phases. The first phase typically corresponds to low strengths of 0.04 - 0.12
MPa. In 2/3 of cases, the first phase was catastrophic or nearly catastrophic
with at least 40% of mass lost. The second phase corresponds to 0.9 - 5 MPa for
confirmed meteorite falls and to somewhat lower strengths, from about 0.5 MPa
for smaller meteoroids. All these strengths are lower than tensile strengths of
ordinary chondritic meteorites cited in the literature, 20 - 40 MPa. We
interpret the second phase as being due by cracks in meteoroids and the first
phase as separation of weakly cemented fragments, which reaccumulated at
surfaces of asteroids after asteroid collisions. | astro-ph_EP |
Planet Occurrence Rate Correlated to Stellar Dynamical History: Evidence
from Kepler and Gaia: The dynamical history of stars influences the formation and evolution of
planets significantly. To explore the influence of dynamical history on planet
formation and evolution from observations, we assume that stars who experienced
significantly different dynamical histories tend to have different relative
velocities. Utilizing the accurate Gaia-Kepler Stellar Properties Catalog, we
select single main-sequence stars and divide these stars into three groups
according to their relative velocities, i.e. high-V, medium-V, and low-V stars.
After considering the known biases from Kepler data and adopting prior and
posterior correction to minimize the influence of stellar properties on planet
occurrence rate, we find that high-V stars have a lower occurrence rate of
super-Earths and sub-Neptunes (1--4 R$_{\rm \oplus}$, P<100 days) and higher
occurrence rate of sub-Earth (0.5--1 R$_{ \oplus}$, P<30 days) than low-V
stars. Additionally, high-V stars have a lower occurrence rate of hot Jupiter
sized planets (4--20 R$_{\oplus}$, P<10 days) and a slightly higher occurrence
rate of warm or cold Jupiter sized planets (4--20 R$_{\oplus}$, 10<P<400 days).
After investigating the multiplicity and eccentricity, we find that high-V
planet hosts prefer a higher fraction of multi-planets systems and lower
average eccentricity, which is consistent with the eccentricity-multiplicity
dichotomy of Kepler planetary systems. All these statistical results favor the
scenario that the high-V stars with large relative velocity may experience
fewer gravitational events, while the low-V stars may be influenced by stellar
clustering significantly. | astro-ph_EP |
A roadmap to the efficient and robust characterization of temperate
terrestrial planet atmospheres with JWST: Ultra-cool dwarf stars are abundant, long-lived, and uniquely suited to
enable the atmospheric study of transiting terrestrial companions with JWST.
Amongst them, the most prominent is the M8.5V star TRAPPIST-1 and its seven
planets, which have been the favored targets of eight JWST Cycle 1 programs.
While Cycle 1 observations have started to yield preliminary insights into the
planets, they have also revealed that their atmospheric exploration requires a
better understanding of their host star. Here, we propose a roadmap to
characterize the TRAPPIST-1 system -- and others like it -- in an efficient and
robust manner. We notably recommend that -- although more challenging to
schedule -- multi-transit windows be prioritized to constrain stellar
heterogeneities and gather up to 2$\times$ more transits per JWST hour spent.
We conclude that in such systems planets cannot be studied in isolation by
small programs, thus large-scale community-supported programs should be
supported to enable the efficient and robust exploration of terrestrial
exoplanets in the JWST era. | astro-ph_EP |
Thermal structure of circumbinary discs: Circumbinary planets should be
icy not rocky: The process of forming a circumbinary planet is thought to be intimately
related to the structure of the nascent circumbinary disc. It has been shown
that the structure of a circumbinary disc depends strongly on 3-dimensional
effects and on the detailed modelling of the thermodynamics. Here, we employ
3-dimensional hydrodynamical simulations, combined with a proper treatment of
the thermal physics using the RADMC-3D radiation transport code, to examine the
location of the snow line in circumbinary discs. The models have application to
the circumbinary planets that have been discovered in recent years by the
Kepler and TESS transit surveys. We find that the snow line is located in a
narrow region of the circumbinary disc, close to the inner cavity that is
carved out by the central binary, at typical orbital distances of $\sim 1.5-2$
AU for the system parameters considered. In this region, previous work has
shown that both grain growth and pebble accretion are likely to be inefficient
because of the presence of hydrodynamical turbulence. Hence, in situ planet
formation interior to the snow line is unlikely to occur and circumbinary
planets should preferentially be icy, not rocky. | astro-ph_EP |
Astrometric follow-up observations of directly imaged sub-stellar
companions to young stars and brown dwarfs: The formation of massive planetary or brown dwarf companions at large
projected separations from their host star is not yet well understood. In order
to put constraints on formation scenarios we search for signatures in the orbit
dynamics of the systems. We are specifically interested in the eccentricities
and inclinations since those parameters might tell us about the dynamic history
of the systems and where to look for additional low-mass sub-stellar
companions. For this purpose we utilized VLT/NACO to take several well
calibrated high resolution images of 6 target systems and analyze them together
with available literature data points of those systems as well as Hubble Space
Telescope archival data. We used a statistical Least-Squares Monte-Carlo
approach to constrain the orbit elements of all systems that showed significant
differential motion of the primary star and companion. We show for the first
time that the GQ Lup system shows significant change in both separation and
position angle. Our analysis yields best fitting orbits for this system, which
are eccentric (e between 0.21 and 0.69), but can not rule out circular orbits
at high inclinations. Given our astrometry we discuss formation scenarios of
the GQ Lup system. In addition, we detected an even fainter new companion
candidate to GQ Lup, which is most likely a background object. We also updated
the orbit constraints of the PZ Tel system, confirming that the companion is on
a highly eccentric orbit with e > 0.62. Finally we show with a high
significance, that there is no orbital motion observed in the cases of the DH
Tau, HD 203030 and 1RXS J160929.1-210524 systems and give the most precise
relative astrometric measurement of the UScoCTIO 108 system to date. | astro-ph_EP |
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