208 research outputs found
Studying atmosphere-dominated hot Jupiter Kepler phase curves: Evidence that inhomogeneous atmospheric reflection is common
(abridged) We identify 3 Kepler transiting planets, Kepler-7b, Kepler-12b,
and Kepler-41b, whose orbital phase-folded light curves are dominated by
planetary atmospheric processes including thermal emission and reflected light,
while the impact of non-atmospheric (i.e. gravitational) processes, including
beaming (Doppler boosting) and tidal ellipsoidal distortion, is negligible.
Therefore, those systems allow a direct view of their atmospheres without being
hampered by the approximations used in the inclusion of both atmospheric and
non-atmospheric processes when modeling the phase curve shape. Here we analyze
Kepler-12b and Kepler-41b atmosphere based on their Kepler phase curve, while
the analysis of Kepler-7b was presented elsewhere. The model we used
efficiently computes reflection and thermal emission contributions to the phase
curve, including inhomogeneous atmospheric reflection due to longitudinally
varying cloud coverage. We confirm Kepler-12b and Kepler-41b show a westward
phase shift between the brightest region on the planetary surface and the
substellar point, similar to Kepler-7b. We find that reflective clouds located
on the west side of the substellar point can explain the phase shift. The
existence of inhomogeneous atmospheric reflection in all 3 of our targets,
selected due to their atmosphere-dominated Kepler phase curve, suggests this
phenomenon is common. Therefore it is likely to be present also in planetary
phase curves that do not allow a direct view of the planetary atmosphere as
they contain additional orbital processes. We discuss the implications of a
bright-spot shift on the analysis of phase curves where both atmospheric and
gravitational processes appear. We also discuss the potential detection of
non-transiting but otherwise similar planets, whose mass is too small to show a
gravitational photometric signal but their atmospheric signal is detectable.Comment: V2: Replaced with accepted version, Appendix B Figures 1 and 2 are in
decreased resolutio
Photochemistry in Terrestrial Exoplanet Atmospheres III: Photochemistry and Thermochemistry in Thick Atmospheres on Super Earths and Mini Neptunes
Some super Earths and mini Neptunes will likely have thick atmospheres that
are not H2-dominated. We have developed a photochemistry-thermochemistry
kinetic-transport model for exploring the compositions of thick atmospheres on
super Earths and mini Neptunes, applicable for both H2-dominated atmospheres
and non-H2-dominated atmospheres. Using this model to study thick atmospheres
for wide ranges of temperatures and elemental abundances, we classify them into
hydrogen-rich atmospheres, water-rich atmospheres, oxygen-rich atmospheres, and
hydrocarbon-rich atmospheres. We find that carbon has to be in the form of CO2
rather than CH4 or CO in a H2-depleted water-dominated thick atmosphere, and
that the preferred loss of light elements from an oxygen-poor carbon-rich
atmosphere leads to formation of unsaturated hydrocarbons (C2H2 and C2H4). We
apply our self-consistent atmosphere models to compute spectra and diagnostic
features for known transiting low-mass exoplanets GJ 1214 b, HD 97658 b, and 55
Cnc e. For GJ 1214 b like planets we find that (1) C2H2 features at 1.0 and 1.5
micron in transmission and C2H2 and C2H4 features at 9-14 micron in thermal
emission are diagnostic for hydrocarbon-rich atmospheres; (2) a detection of
water-vapor features and a confirmation of nonexistence of methane features
would provide sufficient evidence for a water-dominated atmosphere. In general,
our simulations show that chemical stability has to be taken into account when
interpreting the spectrum of a super Earth/mini Neptune. Water-dominated
atmospheres only exist for carbon to oxygen ratios much lower than the solar
ratio, suggesting that this kind of atmospheres could be rare.Comment: Accepted for publication on Ap
A Case for an Atmosphere on Super-Earth 55 Cancri e
One of the primary questions when characterizing Earth-sized and
super-Earth-sized exoplanets is whether they have a substantial atmosphere like
Earth and Venus or a bare-rock surface like Mercury. Phase curves of the
planets in thermal emission provide clues to this question, because a
substantial atmosphere would transport heat more efficiently than a bare-rock
surface. Analyzing phase curve photometric data around secondary eclipse has
previously been used to study energy transport in the atmospheres of hot
Jupiters. Here we use phase curve, Spitzer time-series photometry to study the
thermal emission properties of the super-Earth exoplanet 55 Cancri e. We
utilize a semi-analytical framework to fit a physical model to the infrared
photometric data at 4.5 micron. The model uses parameters of planetary
properties including Bond albedo, heat redistribution efficiency (i.e., ratio
between radiative timescale and advective timescale of the atmosphere), and
atmospheric greenhouse factor. The phase curve of 55 Cancri e is dominated by
thermal emission with an eastward-shifted hot spot. We determine the heat
redistribution efficiency to be ~1.47, which implies that the advective
timescale is on the same order as the radiative timescale. This requirement
cannot be met by the bare-rock planet scenario because heat transport by
currents of molten lava would be too slow. The phase curve thus favors the
scenario with a substantial atmosphere. Our constraints on the heat
redistribution efficiency translate to an atmospheric pressure of ~1.4 bar. The
Spitzer 4.5-micron band is thus a window into the deep atmosphere of the planet
55 Cancri e.Comment: Accepted for publication on A
The Research on Utilization and Interoperability of XBRL Taxonomy Elements of Listed Companies Financial Report
This article is based on the research on utilization and interoperability of Chinese XBRL taxonomy elements focusing on the improvement of the insufficient XBRL taxonomy elements The authors believe that increase the number of XBRL taxonomy elements can enhance the interoperability of financial reports and accuracy of compiling XBRL software element
Helium Atmospheres on Warm Neptune- and Sub-Neptune-Sized Exoplanets and Applications to GJ 436 b
Warm Neptune- and sub-Neptune-sized exoplanets in orbits smaller than
Mercury's are thought to have experienced extensive atmospheric evolution. Here
we propose that a potential outcome of this atmospheric evolution is the
formation of helium-dominated atmospheres. The hydrodynamic escape rates of
Neptune- and sub-Neptune-sized exoplanets are comparable to the
diffusion-limited escape rate of hydrogen, and therefore the escape is heavily
affected by diffusive separation between hydrogen and helium. A helium
atmosphere can thus be formed -- from a primordial hydrogen-helium atmosphere
-- via atmospheric hydrodynamic escape from the planet. The helium atmosphere
has very different abundances of major carbon and oxygen species from those of
a hydrogen atmosphere, leading to distinctive transmission and thermal emission
spectral features. In particular, the hypothesis of a helium-dominated
atmosphere can explain the thermal emission spectrum of GJ 436 b, a warm
Neptune-sized exoplanet, while also consistent with the transmission spectrum.
This model atmosphere contains trace amounts of hydrogen, carbon, and oxygen,
with the predominance of CO over CH4 as the main form of carbon. With our
atmospheric evolution model, we find that if the mass of the initial atmosphere
envelope is 1E-3 planetary mass, hydrodynamic escape can reduce the hydrogen
abundance in the atmosphere by several orders of magnitude in ~10 billion
years. Observations of exoplanet transits may thus detect signatures of helium
atmospheres and probe the evolutionary history of small exoplanets.Comment: ApJ, accepte
Photochemical Oxygen in Non-1-bar CO_2 Atmospheres of Terrestrial Exoplanets
Atmospheric chemistry models have shown that molecular oxygen can build up in CO_2-dominated atmospheres on potentially habitable exoplanets without input of life. Existing models typically assume a surface pressure of 1 bar. Here we present model scenarios of CO_2-dominated atmospheres with the surface pressure ranging from 0.1 to 10 bars, while keeping the surface temperature at 288 K. We use a one-dimensional photochemistry model to calculate the abundance of O_2 and other key species, for outgassing rates ranging from a Venus-like volcanic activity up to 20 times Earth-like activity. The model maintains the redox balance of the atmosphere and the ocean, and includes the pressure dependency of outgassing on the surface pressure. Our calculations show that the surface pressure is a controlling parameter in the photochemical stability and oxygen buildup of CO_2-dominated atmospheres. The mixing ratio of O_2 monotonically decreases as the surface pressure increases at very high outgassing rates, whereas it increases as the surface pressure increases at lower-than-Earth outgassing rates. Abiotic O_2 can only build up to the detectable level, defined as 10^(−3) in volume mixing ratio, in 10-bar atmospheres with the Venus-like volcanic activity rate and the reduced outgassing rate of H_2 due to the high surface pressure. Our results support the search for biological activities and habitability via atmospheric O_2 on terrestrial planets in the habitable zone of Sun-like stars
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