Distant planet GJ 1132 b is a sub-Neptune that lost its atmosphere due to being too close to its young, hot star and faced with intense radiation, making this sub-Neptune more Earth-sized. But wait! What’s this the Hubble Space Telescope has detected? An atmosphere? It seems that, in the face of losing its atmosphere, GJ 1132 b found a way to acquire a new one.

This secondary atmosphere was analyzed based on a combination of Hubble’s observations and some computer modeling. Instead of the primordial hydrogen/helium atmosphere, atmosphere 2.0 is made of hydrogen, hydrogen cyanide, methane, and an aerosol haze. The haze is likely photochemically produced hydrocarbons, similar to the smog that can form here on Earth.

Even more interesting, this new atmosphere has possibly been influenced by volcanic processes in the interior and on the surface of GJ 1132 b, and those processes are due to the tidal heating from the gravitational pull of the star and another planet, plus the elliptical orbit which gives those pulls some needed variation.

Lead author Mark Swain sums up the work, soon to be published in The Astronomical Journal: How many terrestrial planets don’t begin as terrestrials? Some may start as sub-Neptunes, and they become terrestrials through a mechanism that photo-evaporates the primordial atmosphere. This process works early in a planet’s life when the star is hotter. Then the star cools down and the planet’s just sitting there. So you’ve got this mechanism where you can cook off the atmosphere in the first 100 million years, and then things settle down. And if you can regenerate the atmosphere, maybe you can keep it.

Chalk another point up in the column for sub-Neptunes being able to shift to super-Earths, I guess.

More Information

NASA Goddard press release

Hubble Telescope press release

“Detection of an Atmosphere on a Rocky Exoplanet,” Mark R. Swain et al., to be published in The Astronomical Journal (preprint on arxiv.org)