Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Billy Edwards
Quentin Changeat
Angelos Tsiaras
Kai Hou Yip
Ahmed F. Al-Refaie
Lara Anisman
Michelle F. Bieger
Amelie Gressier
Sho Shibata
Nour Skaf
Jeroen Bouwman
James Y-K. Cho
Masahiro Ikoma
Olivia Venot
Ingo Waldmann
Pierre-Olivier Lagage
Giovanna Tinetti
Abstract： We present the analysis of the atmospheres of 70 gaseous extrasolar planets via transit spectroscopy with Hubble's Wide Field Camera 3 (WFC3). For over half of these, we statistically detect spectral modulation which our retrievals attribute to molecular species. Among these, we use Bayesian Hierarchical Modelling to search for chemical trends with bulk parameters. We use the extracted water abundance to infer the atmospheric metallicity and compare it to the planet's mass. We also run chemical equilibrium retrievals, fitting for the atmospheric metallicity directly. However, although previous studies have found evidence of a mass-metallicity trend, we find no such relation within our data. For the hotter planets within our sample, we find evidence for thermal dissociation of dihydrogen and water via the H$^-$ opacity. We suggest that the general lack of trends seen across this population study could be due to i) the insufficient spectral coverage offered by HST WFC3 G141, ii) the lack of a simple trend across the whole population, iii) the essentially random nature of the target selection for this study or iv) a combination of all the above. We set out how we can learn from this vast dataset going forward in an attempt to ensure comparative planetology can be undertaken in the future with facilities such as JWST, Twinkle and Ariel. We conclude that a wider simultaneous spectral coverage is required as well as a more structured approach to target selection.
Peer Review Status:
Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Lili Alderson
Hannah R. Wakeford
Munazza K. Alam
Natasha E. Batalha
Joshua D. Lothringer
Jea Adams Redai
Saugata Barat
Jonathan Brande
Mario Damiano
Tansu Daylan
Néstor Espinoza
Laura Flagg
Jayesh M. Goyal
David Grant
Renyu Hu
Julie Inglis
Elspeth K. H. Lee
Thomas Mikal-Evans
Lakeisha Ramos-Rosado
Pierre-Alexis Roy
Abstract： Measuring the abundances of carbon and oxygen in exoplanet atmospheres is considered a crucial avenue for unlocking the formation and evolution of exoplanetary systems. Access to an exoplanet's chemical inventory requires high-precision observations, often inferred from individual molecular detections with low-resolution space-based and high-resolution ground-based facilities. Here we report the medium-resolution (R$\sim$600) transmission spectrum of an exoplanet atmosphere between 3-5 $\mu$m covering multiple absorption features for the Saturn-mass exoplanet WASP-39b, obtained with JWST NIRSpec G395H. Our observations achieve 1.46x photon precision, providing an average transit depth uncertainty of 221 ppm per spectroscopic bin, and present minimal impacts from systematic effects. We detect significant absorption from CO$_2$ (28.5$\sigma$) and H$_2$O (21.5$\sigma$), and identify SO$_2$ as the source of absorption at 4.1 $\mu$m (4.8$\sigma$). Best-fit atmospheric models range between 3 and 10x solar metallicity, with sub-solar to solar C/O ratios. These results, including the detection of SO$_2$, underscore the importance of characterising the chemistry in exoplanet atmospheres, and showcase NIRSpec G395H as an excellent mode for time series observations over this critical wavelength range.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Adina D. Feinstein
Michael Radica
Luis Welbanks
Catriona Anne Murray
Kazumasa Ohno
Louis-Philippe Coulombe
Néstor Espinoza
Jacob L. Bean
Johanna K. Teske
Björn Benneke
Michael R. Line
Zafar Rustamkulov
Arianna Saba
Angelos Tsiaras
Joanna K. Barstow
Jonathan J. Fortney
Peter Gao
Heather A. Knutson
Ryan J. MacDonald
Thomas Mikal-Evans
Abstract： Transmission spectroscopy provides insight into the atmospheric properties and consequently the formation history, physics, and chemistry of transiting exoplanets. However, obtaining precise inferences of atmospheric properties from transmission spectra requires simultaneously measuring the strength and shape of multiple spectral absorption features from a wide range of chemical species. This has been challenging given the precision and wavelength coverage of previous observatories. Here, we present the transmission spectrum of the Saturn-mass exoplanet WASP-39b obtained using the SOSS mode of the NIRISS instrument on the JWST. This spectrum spans $0.6 - 2.8 \mu$m in wavelength and reveals multiple water absorption bands, the potassium resonance doublet, as well as signatures of clouds. The precision and broad wavelength coverage of NIRISS-SOSS allows us to break model degeneracies between cloud properties and the atmospheric composition of WASP-39b, favoring a heavy element enhancement ("metallicity") of $\sim 10 - 30 \times$ the solar value, a sub-solar carbon-to-oxygen (C/O) ratio, and a solar-to-super-solar potassium-to-oxygen (K/O) ratio. The observations are best explained by wavelength-dependent, non-gray clouds with inhomogeneous coverage of the planet's terminator.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Eva-Maria Ahrer
Kevin B. Stevenson
Megan Mansfield
Sarah E. Moran
Jonathan Brande
Giuseppe Morello
Catriona A. Murray
Nikolay K. Nikolov
Dominique J. M. Petit dit de la Roche
Everett Schlawin
Peter J. Wheatley
Sebastian Zieba
Natasha E. Batalha
Mario Damiano
Jayesh M Goyal
Monika Lendl
Joshua D. Lothringer
Sagnick Mukherjee
Kazumasa Ohno
Natalie M. Batalha
Abstract： Measuring the metallicity and carbon-to-oxygen (C/O) ratio in exoplanet atmospheres is a fundamental step towards constraining the dominant chemical processes at work and, if in equilibrium, revealing planet formation histories. Transmission spectroscopy provides the necessary means by constraining the abundances of oxygen- and carbon-bearing species; however, this requires broad wavelength coverage, moderate spectral resolution, and high precision that, together, are not achievable with previous observatories. Now that JWST has commenced science operations, we are able to observe exoplanets at previously uncharted wavelengths and spectral resolutions. Here we report time-series observations of the transiting exoplanet WASP-39b using JWST's Near InfraRed Camera (NIRCam). The long-wavelength spectroscopic and short-wavelength photometric light curves span 2.0 - 4.0 $\mu$m, exhibit minimal systematics, and reveal well-defined molecular absorption features in the planet's spectrum. Specifically, we detect gaseous H$_2$O in the atmosphere and place an upper limit on the abundance of CH$_4$. The otherwise prominent CO$_2$ feature at 2.8 $\mu$m is largely masked by H$_2$O. The best-fit chemical equilibrium models favour an atmospheric metallicity of 1-100$\times$ solar (i.e., an enrichment of elements heavier than helium relative to the Sun) and a sub-stellar carbon-to-oxygen (C/O) ratio. The inferred high metallicity and low C/O ratio may indicate significant accretion of solid materials during planet formation or disequilibrium processes in the upper atmosphere.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Louis-Philippe Coulombe
Björn Benneke
Ryan Challener
Anjali A. A. Piette
Lindsey S. Wiser
Megan Mansfield
Ryan J. MacDonald
Hayley Beltz
Adina D. Feinstein
Michael Radica
Arjun B. Savel
Leonardo A. Dos Santos
Jacob L. Bean
Vivien Parmentier
Ian Wong
Emily Rauscher
Thaddeus D. Komacek
Eliza M. -R. Kempton
Xianyu Tan
Mark Hammond
Abstract： Close-in giant exoplanets with temperatures greater than 2,000 K (''ultra-hot Jupiters'') have been the subject of extensive efforts to determine their atmospheric properties using thermal emission measurements from the Hubble and Spitzer Space Telescopes. However, previous studies have yielded inconsistent results because the small sizes of the spectral features and the limited information content of the data resulted in high sensitivity to the varying assumptions made in the treatment of instrument systematics and the atmospheric retrieval analysis. Here we present a dayside thermal emission spectrum of the ultra-hot Jupiter WASP-18b obtained with the NIRISS instrument on JWST. The data span 0.85 to 2.85 $\mu$m in wavelength at an average resolving power of 400 and exhibit minimal systematics. The spectrum shows three water emission features (at $>$6$\sigma$ confidence) and evidence for optical opacity, possibly due to H$^-$, TiO, and VO (combined significance of 3.8$\sigma$). Models that fit the data require a thermal inversion, molecular dissociation as predicted by chemical equilibrium, a solar heavy element abundance (''metallicity'', M/H = 1.03$_{-0.51}^{+1.11}$ $\times$ solar), and a carbon-to-oxygen (C/O) ratio less than unity. The data also yield a dayside brightness temperature map, which shows a peak in temperature near the sub-stellar point that decreases steeply and symmetrically with longitude toward the terminators.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Shang-Min Tsai
Elspeth K. H. Lee
Diana Powell
Peter Gao
Xi Zhang
Julianne Moses
Eric Hébrard
Olivia Venot
Vivien Parmentier
Sean Jordan
Renyu Hu
Munazza K. Alam
Lili Alderson
Natalie M. Batalha
Jacob L. Bean
Björn Benneke
Carver J. Bierson
Ryan P. Brady
Ludmila Carone
Aarynn L. Carter
Abstract： Photochemistry is a fundamental process of planetary atmospheres that is integral to habitability, atmospheric composition and stability, and aerosol formation. However, no unambiguous photochemical products have been detected in exoplanet atmospheres to date. Here we show that photochemically produced sulphur dioxide (SO$_2$) is present in the atmosphere of the hot, giant exoplanet WASP-39b, as constrained by data from the JWST Transiting Exoplanet Early Release Science Program and informed by a suite of photochemical models. We find that SO$_2$ is produced by successive oxidation of sulphur radicals freed when hydrogen sulphide (H$_2$S) is destroyed. The SO$_2$ distribution computed by the photochemical models robustly explains the 4.05 $\mu$m spectral feature seen in JWST transmission spectra [Rustamkulov et al.(submitted), Alderson et al.(submitted)] and leads to observable features at ultraviolet and thermal infrared wavelengths not available from the current observations. The sensitivity of the SO$_2$ feature to the enrichment of heavy elements in the atmosphere ("metallicity") suggests that it can be used as a powerful tracer of atmospheric properties, with our results implying a metallicity of $\sim$10$\times$ solar for WASP-39b. Through providing improved constraints on bulk metallicity and sulphur abundance, the detection of SO$_2$ opens a new avenue for the investigation of giant-planet formation. Our work demonstrates that sulphur photochemistry may be readily observable for exoplanets with super-solar metallicity and equilibrium temperatures $\gtrsim$750 K. The confirmation of photochemistry through the agreement between theoretical predictions and observational data is pivotal for further atmospheric characterisation studies.
Peer Review Status:Awaiting Review
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