Unusual Exoplanet Might Be Regrowing Its Atmosphere

Remnants of the first atmosphere trapped under the planet’s thin crust might escape through volcanic eruptions

An artist's rendition of the exoplanet in outer space shows its crackly surface, where lava seeps up through a thin crust of rock
Exoplanet GJ 1132 b was discovered in 2015 and is about 41 light years away from Earth NASA, ESA, and R. Hurt (IPAC/Caltech)

If at first your atmosphere gets blasted into the void of space, try, try again. That’s the case for exoplanet GJ 1132 b, anyway.

New research, accepted for publication in the Astronomical Journal and posted as a preprint to arXiv on March 10, analyzes images of the planet captured by the Hubble Space Telescope in 2016 and shows that it has a thin atmosphere. The paper presents a theory about how the planet may have lost its first atmosphere and how this new one might have come to be. Although planets in our solar system, including Earth and Mars, have also had multiple atmospheres, GJ 1132 b is the first exoplanet found with a secondary atmosphere, NASA says in a statement.

“You know the universe is a complicated and beautiful place, and does all sorts of things that people don't necessarily imagine until they start investigating,” says Mark Swain, an astronomer at NASA’s Jet Propulsion Laboratory, to Passant Rabie at Inverse. The find shows that other exoplanets that lose their original atmospheres might have a chance at another, he says. “They may have had a way under the right circumstances to reestablish… a hydrogen-rich atmosphere.”

GJ 1132 b has been the subject of close scrutiny since it was discovered in 2015 by a team at the Harvard-Smithsonian Center for Astrophysics, reports Arwen Rimmer for Astronomy magazine. The exoplanet is about 41 light years from Earth, and when it first formed, it resembled a small Neptune. But early in its lifetime, GJ 1132 b lost the gas giant-defining atmosphere, and now it’s a rocky planet about 1.6 times larger than Earth.

Many characteristics set Earth and GJ 1132 b apart: the exoplanet’s atmosphere is toxic, made of hydrogen, methane and hydrogen cyanide. It’s also very hot, at about 440 degrees Fahrenheit, and lacks mountains and other rough terrain because the top layer of the planet is so thin. It only has a few hundred feet of solid material on its surface, which sit on top of magma.

“It’s probably a lot like walking around on one of the lava fields in Hawaii where you can look down in the cracks and see the growing magma, but the whole world might look like that,” says Swain to Inverse.

The exoplanet’s liquid layer is key to the researchers’ theory about where the secondary atmosphere may have come from. According to the paper, the researchers suggest that the first, Neptune-like atmosphere was blasted away by the closest star within the first 100 million years of the planet’s lifetime.

“It is very likely that the planet lost everything at the very beginning,” says study co-author Raissa Estrela, a planetary scientist at JPL, to Astronomy magazine. “But the transit observations show spectral features which means there definitely is an atmosphere.”

The researchers suggest that some of the gases in the exoplanet’s first atmosphere may have dissolved into the molten mantle, creating a reservoir. Through volcanic activity, the long-lost atmospheric gases might now be shooting out of the ground like the undead and returning to their place above the planet’s surface. The chemical makeup detected by Hubble included the kinds of signatures that they expected from a hydrogen-rich magma layer.

University of Chicago astrophysicist Leslie Rogers, who was not involved in the study, tells Astronomy magazine that the study is not yet conclusive, in part because it’s difficult to study distant atmospheres with Hubble imagery. (The researchers analyzed the light that comes from GJ 1132 b’s star, passes around the planet, and shines toward the space telescope.) However, Rogers adds, “the observation hints at an unusual world which is certainly worth another look.”

The research team led by Swain hopes to get a closer look at the exoplanet once the James Webb Space Telescope is up and running. The telescope has faced years of delays during its development and is currently scheduled to launch in October 2021. The JWST is designed for observing exoplanets, so the researchers hope to better understand how GJ 1132 b stays hot, look for stronger evidence of its atmosphere, and figure out where its volcanic activity might be taking place.

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