142 research outputs found
On the heat redistribution of the hot transiting exoplanet WASP-18b
The energy deposition and redistribution in hot Jupiter atmospheres is not
well understood currently, but is a major factor for their evolution and
survival. We present a time dependent radiative transfer model for the
atmosphere of WASP-18b which is a massive (10 MJup) hot Jupiter (Teq ~ 2400 K)
exoplanet orbiting an F6V star with an orbital period of only 0.94 days. Our
model includes a simplified parametrisation of the day-to-night energy
redistribution by a modulation of the stellar heating mimicking a solid body
rotation of the atmosphere. We present the cases with either no rotation at all
with respect to the synchronously rotating reference frame or a fast
differential rotation. The results of the model are compared to previous
observations of secondary eclipses of Nymeyer et al. (2011) with the Spitzer
Space Telescope. Their observed planetary flux suggests that the efficiency of
heat distribution from the day-side to the night-side of the planet is
extremely inefficient. Our results are consistent with the fact that such large
day-side fluxes can be obtained only if there is no rotation of the atmosphere.
Additionally, we infer light curves of the planet for a full orbit in the two
Warm Spitzer bandpassses for the two cases of rotation and discuss the
observational differences.Comment: 4 figures, accepted for publication in Icaru
The atmospheric chemistry of the warm Neptune GJ 3470b: influence of metallicity and temperature on the CH4/CO ratio
Current observation techniques are able to probe the atmosphere of some giant
exoplanets and get some clues about their atmospheric composition. However, the
chemical compositions derived from observations are not fully understood, as
for instance in the case of the CH4/CO abundance ratio, which is often inferred
different from what has been predicted by chemical models. Recently, the warm
Neptune GJ3470b has been discovered and because of its close distance from us
and high transit depth, it is a very promising candidate for follow up
characterisation of its atmosphere. We study the atmospheric composition of
GJ3470b in order to compare with the current observations of this planet, to
prepare the future ones, but also as a typical case study to understand the
chemical composition of warm (sub-)Neptunes. The metallicity of such
atmospheres is totally uncertain, and vary probably to values up to 100x solar.
We explore the space of unknown parameters to predict the range of possible
atmospheric compositions. Within the parameter space explored we find that in
most cases methane is the major carbon-bearing species. We however find that in
some cases, typically for high metallicities with a sufficiently high
temperature the CH4/CO abundance ratio can become lower than unity, as
suggested by some multiwavelength photometric observations of other warm
(sub-)Neptunes, such as GJ1214b and GJ436b. As for the emission spectrum of
GJ3470b, brightness temperatures at infrared wavelengths may vary between 400
and 800K depending on the thermal profile and metallicity. Combined with a hot
temperature profile, a substantial enrichment in heavy elements by a factor of
100 with respect to the solar composition can shift the carbon balance in
favour of carbon monoxide at the expense of CH4. Nevertheless, current
observations of this planet do not allow yet to determine which model is more
accurate.Comment: 12 pages, 8 figures, accepted in Astronomy & Astrophysic
Impact of Cosmic Rays on Atmospheric Ion Chemistry and Spectral Transmission Features of TRAPPIST-1e
Ongoing observing projects like the James Webb Space Telescope and future missions offer the chance to characterize Earth-like exoplanetary atmospheres. Thereby, M dwarfs are preferred targets for transit observations, for example, due to their favorable planet–star contrast ratio. However, the radiation and particle environment of these cool stars could be far more extreme than what we know from the Sun. Thus, knowing the stellar radiation and particle environment and its possible influence on detectable biosignatures—in particular, signs of life like ozone and methane—is crucial to understanding upcoming transit spectra. In this study, with the help of our unique model suite INCREASE, we investigate the impact of a strong stellar energetic particle event on the atmospheric ionization, neutral and ion chemistry, and atmospheric biosignatures of TRAPPIST-1e. Therefore, transit spectra for six scenarios are simulated. We find that a Carrington-like event drastically increases atmospheric ionization and induces substantial changes in ion chemistry and spectral transmission features: all scenarios show high event-induced amounts of nitrogen dioxide (i.e., at 6.2 μm), a reduction of the atmospheric transit depth in all water bands (i.e., at 5.5–7.0 μm), a decrease of the methane bands (i.e., at 3.0–3.5 μm), and depletion of ozone (i.e., at ∼9.6 μm). Therefore, it is essential to include high-energy particle effects to correctly assign biosignature signals from, e.g., ozone and methane. We further show that the nitric acid feature at 11.0–12.0 μm, discussed as a proxy for stellar particle contamination, is absent in wet-dead atmospheres
The Dual Origin of the Terrestrial Atmosphere
The origin of the terrestrial atmosphere is one of the most puzzling enigmas
in the planetary sciences. It is suggested here that two sources contributed to
its formation, fractionated nebular gases and accreted cometary volatiles.
During terrestrial growth, a transient gas envelope was fractionated from
nebular composition. This transient atmosphere was mixed with cometary
material. The fractionation stage resulted in a high Xe/Kr ratio, with xenon
being more isotopically fractionated than krypton. Comets delivered volatiles
having low Xe/Kr ratios and solar isotopic compositions. The resulting
atmosphere had a near-solar Xe/Kr ratio, almost unfractionated krypton
delivered by comets, and fractionated xenon inherited from the fractionation
episode. The dual origin therefore provides an elegant solution to the
long-standing "missing xenon" paradox. It is demonstrated that such a model
could explain the isotopic and elemental abundances of Ne, Ar, Kr, and Xe in
the terrestrial atmosphere.Comment: Icarus, in press, 31 pages, 6 tables, and 6 figure
A Spitzer Transmission Spectrum for the Exoplanet GJ 436b, Evidence for Stellar Variability, and Constraints on Dayside Flux Variations
In this paper we describe a uniform analysis of eight transits and eleven
secondary eclipses of the extrasolar planet GJ 436b obtained in the 3.6, 4.5,
and 8.0 micron bands using the IRAC instrument on the Spitzer Space Telescope
between UT 2007 June 29 and UT 2009 Feb 4. We find that the best-fit transit
depths for visits in the same bandpass can vary by as much as 8% of the total
(4.7 sigma significance) from one epoch to the next. Although we cannot
entirely rule out residual detector effects or a time-varying, high-altitude
cloud layer in the planet's atmosphere as the cause of these variations, we
consider the occultation of active regions on the star in a subset of the
transit observations to be the most likely explanation. We reconcile the
presence of magnetically active regions with the lack of significant visible or
infrared flux variations from the star by proposing that the star's spin axis
is tilted with respect to our line of sight, and that the planet's orbit is
therefore likely to be misaligned. These observations serve to illustrate the
challenges associated with transmission spectroscopy of planets orbiting
late-type stars; we expect that other systems, such as GJ 1214, may display
comparably variable transit depths. Our measured 8 micron secondary eclipse
depths are consistent with a constant value, and we place a 1 sigma upper limit
of 17% on changes in the planet's dayside flux in this band. Averaging over the
eleven visits gives us an improved estimate of 0.0452% +/- 0.0027% for the
secondary eclipse depth. We combine timing information from our observations
with previously published data to produce a refined orbital ephemeris, and
determine that the best-fit transit and eclipse times are consistent with a
constant orbital period. [ABRIDGED]Comment: 26 pages, 18 figures, 7 tables in emulateapj format. Accepted for
publication in Ap
Exoplanet phase curves: observations and theory
Phase curves are the best technique to probe the three dimensional structure
of exoplanets' atmospheres. In this chapter we first review current exoplanets
phase curve observations and the particular challenges they face. We then
describe the different physical mechanisms shaping the atmospheric phase curves
of highly irradiated tidally locked exoplanets. Finally, we discuss the
potential for future missions to further advance our understanding of these new
worlds.Comment: Fig.5 has been updated. Table 1 and corresponding figures have been
updated with new values for WASP-103b and WASP-18b. Contains a table
sumarizing phase curve observation
Detection of carbon monoxide's 4.6 micron fundamental band structure in WASP-39b's atmosphere with JWST NIRSpec G395H
Carbon monoxide (CO) is predicted to be the dominant carbon-bearing molecule in giant planet atmospheres and, along with water, is important for discerning the oxygen and therefore carbon-to-oxygen ratio of these planets. The fundamental absorption mode of CO has a broad, double-branched structure composed of many individual absorption lines from 4.3 to 5.1 μm, which can now be spectroscopically measured with JWST. Here we present a technique for detecting the rotational sub-band structure of CO at medium resolution with the NIRSpec G395H instrument. We use a single transit observation of the hot Jupiter WASP-39b from the JWST Transiting Exoplanet Community Early Release Science (JTEC ERS) program at the native resolution of the instrument (R ~ 2700) to resolve the CO absorption structure. We robustly detect absorption by CO, with an increase in transit depth of 264 ± 68 ppm, in agreement with the predicted CO contribution from the best-fit model at low resolution. This detection confirms our theoretical expectations that CO is the dominant carbon-bearing molecule in WASP-39b's atmosphere and further supports the conclusions of low C/O and supersolar metallicities presented in the JTEC ERS papers for WASP-39b
The Need for Laboratory Measurements and Ab Initio Studies to Aid Understanding of Exoplanetary Atmospheres
We are now on a clear trajectory for improvements in exoplanet observations
that will revolutionize our ability to characterize their atmospheric
structure, composition, and circulation, from gas giants to rocky planets.
However, exoplanet atmospheric models capable of interpreting the upcoming
observations are often limited by insufficiencies in the laboratory and
theoretical data that serve as critical inputs to atmospheric physical and
chemical tools. Here we provide an up-to-date and condensed description of
areas where laboratory and/or ab initio investigations could fill critical gaps
in our ability to model exoplanet atmospheric opacities, clouds, and chemistry,
building off a larger 2016 white paper, and endorsed by the NAS Exoplanet
Science Strategy report. Now is the ideal time for progress in these areas, but
this progress requires better access to, understanding of, and training in the
production of spectroscopic data as well as a better insight into chemical
reaction kinetics both thermal and radiation-induced at a broad range of
temperatures. Given that most published efforts have emphasized relatively
Earth-like conditions, we can expect significant and enlightening discoveries
as emphasis moves to the exotic atmospheres of exoplanets.Comment: Submitted as an Astro2020 Science White Pape
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