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Aw, shucks! Promising exoplanet, Proxima b, can't keep an Earth-like atmosphere

Our neighbor solar system Alpha Centauri looked inviting last August when a team of astronomers from the European Southern Observatory (ESO) confirmed the existence of an exoplanet in the habitable zone around the red dwarf star Proxima Centauri. As its name implies, Proxima Centauri is the closest star to our own sun, so the planet, Proxima b, is the closest potentially habitable exoplanet to Earth.

But if agencies were considering sending probes to Proxima b, a new NASA study suggests they should reconsider. The Earth-sized planet probably would not be able to maintain an Earth-like atmosphere, according to the study and that means life as we know it would be practically impossible.

Proxima b is just about four light-years away. Although ESO confirmed its presence by detecting subtle fluctuations in the star’s movement, no one has seen it pass in front of its host star. That means scientists have not yet been able to apply their conventional methods for studying the planet’s atmosphere, so they instead generated models to determine how well its atmosphere held up to its sun.

“We decided to take the only habitable planet we know of so far — Earth — and put it where Proxima b is,” Katherine Garcia-Sage, NASA space scientist and lead author of the study, said in a statement.

In their model, Garcia-Sage and her team swapped Earth for Proxima b, and saw that our planet would be unable to hold onto its atmosphere due to Proxima Centauri’s extreme radiation and frequent solar flares. Proxima b experiences radiation hundreds of time more powerful than Earth does from our sun, which causes molecules as light as hydrogen and as heavy oxygen to get stripped from the planet. As a result, Proxima Centauri would cause an Earth-like atmosphere to degrade 10,000 times faster than Earth’s currently does, according to the study.

“Things can get interesting if an exoplanet holds on to its atmosphere, but Proxima b’s atmospheric loss rates here are so high that habitability is implausible,” said Jeremy Drake, co-author and astrophysicist at the Harvard-Smithsonian Center for Astrophysics. “This questions the habitability of planets around such red dwarfs in general.”

The NASA study was published last week in The Astrophysical Journal Letters.

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