Hot Earth Or Young Venus? A Nearby Transiting Rocky Planet Mystery

Venus and Earth provide an astonishingly different view of the evolution of a rocky planet, raising the question of why these two rocky worlds evolved so differently.

The recently discovered transiting rocky planet LP 890-9c (TOI-4306c, SPECULOOS-2c) is a key to this question. SPECULOOS-2c (1.367 +0.055 -0.039 R_Earth) circles a relatively low-activity nearby (32 pc) M6V star in 8.46 days. SPECULOOS-2c receives 0.906 +/- 0.026 of the flux of modern Earth, putting it very close to the inner edge of the conservative Habitable Zone, where models differ strongly in their prediction of how long Earth-like planets can hold onto their water.

Our atmosphere models show that the transmission spectra of the observable species can tell the difference between a hot, wet Young Earth, a steamy rocky planet caught in a runaway greenhouse at the brink of complete water loss, and a Venus-analog. Distinguishing these scenarios from the planet’s spectra will provide critical new insights into when a hot terrestrial planet loses its water and becomes a Venus.

SPECULOOS-2c is a prime target for observations with JWST. Observing it will also provide key insights to predict the long-term future of Earth.

L. Kaltenegger, R. C. Payne, Z. Lin, J. Kasting, L. Delrez

Comments: submitted ApJL
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM)
Cite as: arXiv:2209.03105 [astro-ph.EP] (or arXiv:2209.03105v1 [astro-ph.EP] for this version)
Submission history
From: Lisa Kaltenegger
[v1] Wed, 7 Sep 2022 12:40:01 UTC (902 KB)
Full paper: https://arxiv.org/abs/2209.03105
Astrobiology