Exoplanet may reveal secrets about the edge of habitability

Exoplanet may reveal secrets about the edge of habitability

Artist impression showing the exoplanet LP 890-9c’s potential evolution from a hot Earth to a desiccated Venus. Credit: Carl Sagan Institute/R. Payne

How close can a rocky planet be to a star, and still sustain water and life? A recently discovered exoplanet may be key to solving that mystery.

“Super-Earth” LP 890-9c (also named SPECULOOS-2c) is providing important insights about conditions at the inner edge of a star’s habitable zone and why Earth and Venus developed so differently, according to new research led by Lisa Kaltenegger, associate professor of astronomy at Cornell University.

Her team found LP 890-9c, which orbits close to the inner edge of its solar system’s habitable zone, would look vastly different depending on whether it still had warm oceans, a steam atmosphere, or if it had lost its water—assuming it once had oceans like Earth’s.

“Looking at this planet will tell us what’s happening on this inner edge of the habitable zone—how long a can maintain habitability when it starts to get hot,” Kaltenegger said. “It will teach us something fundamental about how evolve with increasing starlight, and about what will one day happen to us and Earth.”

Kaltenegger is the lead author of “Hot Earth or Young Venus? A Nearby Transiting Rocky Planet Mystery,” published in Monthly Notices of the Royal Astronomical Society: Letters.

LP 890-9c is one of two super-Earths orbiting a red dwarf star located 100 from Earth, researchers announced last year. They said liquid water or an atmosphere rich in was possible on LP 890-9c, which is about 40% larger than Earth and circles the small, cool star in 8.5 days.

Exoplanet may reveal secrets about the edge of habitability
LP890-9c model scenarios from Hot Earths to Greenhouse atmospheres: (a) Net outgoing infrared (FIR) and incident solar flux (FS) and (b) planetary albedo (Ap) versus surface temperature (TS). Gray lines indicate the models. Credit: Monthly Notices of the Royal Astronomical Society: Letters (2023). DOI: 10.1093/mnrasl/slad064

Those criteria suggested it to be one of the best targets for JWST to study among the known, potentially habitable terrestrial , in addition to the TRAPPIST-1 system.

The team’s models are the first to detail differences in the generated by rocky planets near the ‘s interior boundary, based on variables including the planet’s size, mass, chemical makeup, surface temperature and pressure, atmospheric height and . The calculations were key to estimating how much time JWST would need to confirm the basic composition of an atmosphere—if there is one.

The models span several scenarios thought to reflect stages of rocky planets’ evolution, ranging from a “hot Earth” where life might still be possible, to a desolate Venus featuring a carbon dioxide atmosphere. In between are phases Earth is expected to experience as the sun grows brighter and hotter with age, causing the oceans to gradually evaporate and fill the atmosphere with steam before boiling off entirely.

How long those processes might take is unknown, and the astronomers say LP 890-9c provides a rare opportunity to explore that evolution.

“This planet is the first target where we can test these different scenarios,” Kaltenegger said. “If it’s still a hotter Earth—hot, but with and conditions for life—then the timeline is slower than we thought. If we see that it’s already a full-blown Venus, then the water gets lost fast.”

It’s possible that LP 890-9c has no atmosphere and hosts no life, or that it resembles a Venus with thick clouds that would block light from reflecting and thus yield little information. Deeper investigation promises to provide valuable clues, Kaltenegger said.

“We don’t know what this planet on the edge of habitability could be like, so we have to look,” she said. “This is what real exploration is about.”

More information:
Lisa Kaltenegger et al, Hot Earth or Young Venus? A nearby transiting rocky planet mystery, Monthly Notices of the Royal Astronomical Society: Letters (2023). DOI: 10.1093/mnrasl/slad064

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