Venus as a natural laboratory to infer observational prospects of close-in-orbit rocky exoplanets with a 3D model

Venus is in the spotlight of the public and scientific community after the selection of 3 missions: DAVINCI and VERITAS by NASA and EnVision by ESA/NASA. It remains an open question how Venus and the Earth started so similar but become such different worlds. Thus, studying Venus is essential for understanding the links between planetary evolution and the habitability of terrestrial planets, including those outside our Solar System. Several Earth-sized exoplanets have been recently detected in short-period orbits of a few Earth days around low-mass stars [1]. Those planets have stellar irradiation levels of several times that of the Earth, suggesting that a Venus-like climate is more likely than an Earth-like [2]. Consequently, the atmosphere of our closest planet Venus represents a relevant case to address observational prospects of rocky close-in orbit exoplanets.

In this work we used the Generic Planetary Climate Model (historically known as the LMD Generic GCM), a 3D model developed for exoplanet and paleoclimate studies ([3], [4], [5], [6], [7]), to simulate the atmosphere of two potential Venus’s analogues: TRAPPIST-1c [1] and LP 890-9c [8], both orbiting M-dwarf stars. We assumed that the planets are tidally-locked, and they have evolved into a modern Venus-like atmosphere (e.g. CO₂-dominated, 92-bar surface pressure), with an H₂SO₄ prescribed cloud layer following Venus Express observations ([9]). Our 3D climate simulations show the presence of an eastward equatorial superrotation jet for Trappist-1c (Quirino et al. in preparation), in agreement with previous prediction of highly irradiated synchronous rotators (e.g., [10]), and an effective day-to-night heat redistribution by three superrotation jets (one equatorial and two high-latitudes) for Speculoos-2c (Quirino et al. MNRAS, submitted).

The results will be shown in terms of simulated temperature/wind fields and the potential characterization of the atmosphere of those planets by JWST and future instrumentations discussed. For instance, under the hypothesis that the planets evolved in a modern Venus, our predicted transmission spectra show that even the strongest CO₂ bands around 4.3 μm will be challenging to be detected by the JWST (10 ppm for LP 890-9c and around 40 ppm for Trappist-1c). Those simulations provide new insights for JWST proposals and highlight the influence of clouds on the spectra of hot rocky exoplanets.

References:

[1] Gillon et al. 2017 Nature 542, [2] Kane et al. 2018 ApJ. 869, [3] Forget & Leconte, 2014 Phil. Trans R. Soc.A372., [4] Turbet et al. 2016 A&A 596. A112, [5] Wordsworth et al. 2011 ApJL 733. L48, [6] Leconte et al. 2013, Nature, 504, 286, [7] Turbet et al. 2020 Space Sci. Rev. 216, 100 [8]  Delrez et al. 2022, A&A,Vol.667, id.A59, [9] Haus et al. 2015, PSS, 117, 262, [10] Showman & Polvani 2011, ApJ, 738,71.

Acknowledgments: GG is funded by the Spanish MCIU, the AEI and EC-FEDER funds under project PID2021-126365NB-C21, and IAA’s team acknowledges financial support from the grant CEX2021-001131-S funded by MCIN/AEI/ 10.13039/501100011033