Clouds and Clarity: Revisiting Atmospheric Feature Trends in Neptune-size Exoplanets
Over the last decade, precise exoplanet transmission spectroscopy has revealed the atmospheres of dozens of exoplanets, driven largely by observatories like the Hubble Space Telescope.
One major discovery has been the ubiquity of atmospheric aerosols, often blocking access to exoplanet chemical inventories. Tentative trends have been identified, showing that the clarity of planetary atmospheres may depend on equilibrium temperature. Previous work has often grouped dissimilar planets together in order to increase the statistical power of any trends, but it remains unclear from observed transmission spectra whether these planets exhibit the same atmospheric physics and chemistry.
We present a re-analysis of a smaller, more physically similar sample of 15 exo-Neptune transmission spectra across a wide range of temperatures (200-1000 K). Using condensation cloud and hydrocarbon haze models, we find that the exo-Neptune population is best described by very low cloud sedimentation efficiency (fsed∼0.01) and high metallicity (100× Solar). There is an intrinsic astrophysical scatter of ∼0.5 scale height, perhaps evidence of stochasticity in these planets’ formation processes.
Observers should expect significant attenuation in transmission spectra of Neptune-size exoplanets, up to 6 scale heights for equilibrium temperatures between 500 and 800~K. With JWST’s greater wavelength sensitivity, colder (<500~K) planets should be high-priority targets given their comparative rarity, clearer atmospheres, and the need to distinguish between the “super-puffs” and more typical gas-dominated planets.
Jonathan Brande, Ian J. M. Crossfield, Laura Kreidberg, Caroline V. Morley, Travis Barman, Björn Benneke, Jessie L. Christiansen, Diana Dragomir, Jonathan J. Fortney, Thomas P. Greene, Kevin K. Hardegree-Ullman, Andrew W. Howard, Heather A. Knutson, Joshua D. Lothringer, Thomas Mikal-Evans
Comments: Submitted to ApJL. 11 pages, 3 figures, 4 tables
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2310.07714 [astro-ph.EP] (or arXiv:2310.07714v1 [astro-ph.EP] for this version)
Submission history
From: Jonathan Brande
[v1] Wed, 11 Oct 2023 17:59:06 UTC (390 KB)
https://arxiv.org/abs/2310.07714
Astrobiology, Astrochemistry