Exoplanets & Exomoons

Water Vapour Transit Ambiguities for Habitable M-Earths

By Keith Cowing
Status Report
February 21, 2024
Filed under , , , , , ,
Water Vapour Transit Ambiguities for Habitable M-Earths
CO2 transit spectra for aquaplanets from Group C with varying pN2 (purple), Group A (black), and Group B with 0.1 bar CO2. Although the Group B simulation has two orders of magnitude more CO2, its transit amplitude is smaller than those of the Group C simulations due to the geometries of the systems. However, note that our GCM simulations only include a troposphere; if CO2 is well-mixed on a real planet, spectral features could extend much higher. — astro-ph.EP

We have shown in a recent study, using 3D climate simulations, that dayside land cover has a substantial impact on the climate of a synchronously rotating temperate rocky planet such as Proxima Centauri b.

Building on that result, we generate synthetic transit spectra from our simulations to assess the impact of these land-induced climate uncertainties on water vapour transit signals. We find that distinct climate regimes will likely be very difficult to differentiate in transit spectra, even under the more favourable conditions of smaller planets orbiting ultracool dwarfs.

Further, we show that additional climate ambiguities arise when both land cover and atmosphere mass are unknown, as is likely to be the case for transiting planets. While water vapour may be detectable under favourable conditions, it may be nearly impossible to infer a rocky planet’s surface conditions or climate state from its transit spectrum due to the interdependent effects of land cover and atmosphere mass on surface temperature, humidity, and terminator cloud cover.

Evelyn Macdonald, Kristen Menou, Christopher Lee, Adiv Paradise

Comments: 6 pages, 6 figures. Accepted for publication in MNRAS
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2402.12253 [astro-ph.EP] (or arXiv:2402.12253v1 [astro-ph.EP] for this version)
Focus to learn more
Submission history
From: Evelyn Macdonald
[v1] Mon, 19 Feb 2024 16:09:43 UTC (289 KB)

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) 🖖🏻