Exoplanetology: Exoplanets & Exomoons

Nightside Clouds on Tidally-locked Terrestrial Planets Mimic Atmosphere-Free Scenarios

By Keith Cowing

Status Report

astro-ph.EP

September 13, 2024

Filed under astro-ph.EP, atmosphere, Clouds, exoplanet, habitability, JWST, tidally-locked terrestrial planet, TRAPPIST-1

Nightside Clouds on Tidally-locked Terrestrial Planets Mimic Atmosphere-Free Scenarios — The condensation sequence for a solar composition atmosphere where dashed lines indicate the condensation curves for a variety of typically assumed condensable species. The model planet atmosphere day (red) and night (blue) temperature profiles are shown. In the case of a primordial solar composition atmosphere there may exist a favorable region of temperature phase space where we do not expect significant opacity from condensational clouds (at ∼ 400 – 800 K). However, given the presumed diversity of terrestrial atmospheres, such a favorable region may be unlikely to exist. — astro-ph.EP

We investigate the impact of nightside cloud formation on the observable night-day contrast of tidally-locked terrestrial planet atmospheres.

We demonstrate that, in the case where the planetary dayside is only 10s of Kelvin hotter than the planetary nightside, the presence of optically thick nightside clouds can lead to observations that mimic a planet without an atmosphere, despite the planet actually hosting a significant (10 bar) atmosphere. The scenario presented in this work requires a level of intrinsic atmospheric day/night temperature contrast such that the nightside can form clouds while the dayside is too hot for cloud formation to occur.

This scenario is most likely for hotter terrestrials and terrestrials with low volatile inventories. We thus note that a substantial dayside/nightside temperature difference alone does not robustly indicate that a planet does not host an atmosphere and additional observations and modeling are essential for characterization.

We further discuss several avenues for future study to improve our understanding of the terrestrial planets and how best to characterize them with JWST.

Diana Powell, Robin Wordsworth, Karin Öberg

Comments: Accepted to ApJL, 12 pages, 9 figures
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2409.07542 [astro-ph.EP] (or arXiv:2409.07542v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2409.07542
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Submission history
From: Diana Powell
[v1] Wed, 11 Sep 2024 18:04:52 UTC (3,956 KB)
https://arxiv.org/abs/2409.07542
Astrobiology,

Keith Cowing

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻

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