Friday, October 10, 2025 at 12:15 pm

JILA Foothills Room

Andrea Salazar, Harvard

"Exploring self-consistent habitable Venus scenarios using a novel spin-climate evolution model"

Abstract:

Venus could have been habitable with surface liquid water for up to four billion years if it always had a slow rotation that promoted strong cloud cover. The slow, retrograde rotation of modern Venus is an equilibrium state of two opposing tidal torques: the gravitational and the atmospheric thermal tide. As the atmospheric tide depends strongly on the atmospheric state, past habitable periods would generate a different spin equilibrium from the state we observe today. The coupling between climate and rotation rate via the atmospheric thermal tide has not been considered in previous studies of Venus's habitability history. Here we show using a coupled atmospheric tide and spin evolution model that the strong atmospheric thermal tide generated from a habitable atmosphere pushes the planet into a rapidly rotating regime. This terminates the habitable state rapidly, with a maximum duration of 700 million years if Venus's initial rotation rate was slow and the habitable period began soon after formation. More recent habitable states are even shorter due to the brightening Sun. Only planets with initial rotation periods longer than 4 days reached a modern Venus spin state within the age of the Solar System, potentially necessitating a giant impact during Venus's formation. This work suggests that if Venus had a habitable state, it was early in its history and short-lived. It also implies that Venus-like exoplanets around Sun-like stars are unlikely to be observed in a habitable state.

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