Hot Earth or young Venus? A nearby transiting rocky planet mystery

Press release


September 7, 2022

Temperature profiles and mixing ratios of H2O and CO2 from the SPECULOOS-2c atmosphere models: (top) two Hot Earths (Hot Earth 1 & 2), (middle) two humid greenhouses (Runaway 1 & 2) with a Low and high CO2, and a fully runaway (Runaway 3) greenhouse model (bottom) of CO2-dominated atmospheres (CO2-atm) and a modern Venus VIRA atmosphere (modern Venus).


Venus and Earth offer a startlingly 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 the key to this question. SPECULOOS-2c (1.367 + 0.055 -0.039 R_Earth) circles a nearby M6V star of relatively low activity (32 pc) in 8.46 days. SPECULOOS-2c receives 0.906 +/- 0.026 of the flux from modern Earth, putting it very close to the inner edge of the conservative habitable zone, where models differ sharply in their prediction of how long Earth-like planets can conserve their water.

Our atmosphere models show that the transmission spectra of observable species can tell the difference between a hot and humid Young Earth, a scorching rocky planet caught in a runaway greenhouse on the brink of total water loss, and an analogue of Venus. Distinguishing these scenarios from the planet’s spectra will provide key 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 information for predicting Earth’s long-term future.

L. Kaltenegger, RC Payne, Z. Lin, J. Kasting, L. Delrez

Comments: submitted ApJL
Subjects: Terrestrial 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 release)
Submission history
By: Lisa Kaltenegger
[v1] Wed Sep 07 2022 12:40:01 AM UTC (902 KB)
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Co-founder of SpaceRef, member of the Explorers Club, ex-NASA, external teams, journalist, space and astrobiology, deceased climber.

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