Compositional Diversity in the Atmospheres of Hot Neptunes, with Application to GJ 436b
Julianne I. Moses,Michael R. Line,Channon Visscher,M. R. Richardson,N. Nettelmann,Jonathan J. Fortney,Travis Barman,Kevin B. Stevenson,Nikku Madhusudhan +8 more
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The predicted equilibrium and disequilibrium chemistry of generic hot Neptunes is explored and it is concluded that although the spectral fit from the high-metallicity forward models is not quite as good as the best fit obtained from pure retrieval methods, the atmospheric composition predicted is more physically and chemically plausible in terms of the relative abundance of major constituents.Abstract:
Neptune-sized extrasolar planets that orbit relatively close to their host stars—often called "hot Neptunes"—are common within the known population of exoplanets and planetary candidates. Similar to our own Uranus and Neptune, inefficient accretion of nebular gas is expected produce hot Neptunes whose masses are dominated by elements heavier than hydrogen and helium. At high atmospheric metallicities of 10-10,000 times solar, hot Neptunes will exhibit an interesting continuum of atmospheric compositions, ranging from more Neptune-like, H_2-dominated atmospheres to more Venus-like, CO_2-dominated atmospheres. We explore the predicted equilibrium and disequilibrium chemistry of generic hot Neptunes and find that the atmospheric composition varies strongly as a function of temperature and bulk atmospheric properties such as metallicity and the C/O ratio. Relatively exotic H_2O, CO, CO_2, and even O_2-dominated atmospheres are possible for hot Neptunes. We apply our models to the case of GJ 436b, where we find that a CO-rich, CH_4-poor atmosphere can be a natural consequence of a very high atmospheric metallicity. From comparisons of our results with Spitzer eclipse data for GJ 436b, we conclude that although the spectral fit from the high-metallicity forward models is not quite as good as the best fit obtained from pure retrieval methods, the atmospheric composition predicted by these forward models is more physically and chemically plausible in terms of the relative abundance of major constituents. High-metallicity atmospheres (orders of magnitude in excess of solar) should therefore be considered as a possibility for GJ 436b and other hot Neptunes.read more
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Characterizing transiting exoplanet atmospheres with jwst
Thomas P. Greene,Michael R. Line,Cezar Montero,Jonathan J. Fortney,Jacob Lustig-Yaeger,Kyle Luther +5 more
TL;DR: In this article, the authors explore how well spectra from the James Webb Space Telescope (JWST) will likely constrain bulk atmospheric properties of transiting exoplanets.
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A featureless transmission spectrum for the Neptune-mass exoplanet GJ 436b
TL;DR: Observations of GJ 436b’s atmosphere obtained during transit indicate that the planet's transmission spectrum is featureless, ruling out cloud-free, hydrogen-dominated atmosphere models with an extremely high significance of 48σ.
Journal ArticleDOI
Characterizing transiting exoplanet atmospheres with JWST
Thomas P. Greene,Michael R. Line,Cezar Montero,Jonathan J. Fortney,Jacob Lustig-Yeager,Kyle Luther +5 more
TL;DR: In this article, the authors explore how well James Webb Space Telescope (JWST) spectra will likely constrain bulk atmospheric properties of transiting exoplanets, and they find that the JWST spectra can often constrain the major molecular constituents of clear solar composition atmospheres well.
Journal ArticleDOI
Water vapour absorption in the clear atmosphere of a Neptune-sized exoplanet
Jonathan Fraine,Jonathan Fraine,Jonathan Fraine,Drake Deming,Drake Deming,Björn Benneke,Heather Knutson,Andrés Jordán,Néstor Espinoza,Nikku Madhusudhan,A. Wilkins,Kamen O. Todorov +11 more
TL;DR: Observations of the transmission spectrum of the exoplanet HAT-P-11b from the optical wavelength range to the infrared indicate that the planetary atmosphere is predominantly clear down to an altitude corresponding to about 1 millibar, and sufficiently rich in hydrogen to have a large scale height.
Journal ArticleDOI
From thermal dissociation to condensation in the atmospheres of ultra hot Jupiters: WASP-121b in context
Vivien Parmentier,Vivien Parmentier,Michael R. Line,Jacob L. Bean,Megan Mansfield,Laura Kreidberg,Roxana Lupu,Channon Visscher,Channon Visscher,Jean-Michel Desert,Jonathan J. Fortney,M. Deleuil,Jacob Arcangeli,Adam P. Showman,Mark S. Marley +14 more
TL;DR: The spectral properties of ultra hot Jupiters were investigated in this article, where the authors used the SPARC/MITgcm spectral model to model the atmospheres of the four ultra hot supergiants and discussed more thoroughly the case of WASP-121b.
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