GJ 1132 b may have begun as a mini-Neptune, but is now a rocky world a little bigger than Earth. The planet may have lost one atmosphere but gained another from volcanic activity.

GJ 1132 b, is hypothesized to have begun as a gaseous world with a thick hydrogen blanket of atmosphere. Starting out at several times the diameter of Earth, this so-called “sub-Neptune” is believed to have quickly lost its primordial hydrogen and helium atmosphere due to the intense radiation of the hot, young star it orbits. In a short period of time, such a planet would be stripped down to a bare core about the size of Earth. That’s when things got interesting.

To the surprise of astronomers, Hubble observed an atmosphere which, according to their theory, is a “secondary atmosphere” that is present now. Based on a combination of direct observational evidence and inference through computer modeling, the team reports that the atmosphere consists of molecular hydrogen, hydrogen cyanide, methane and also contains an aerosol haze. Modeling suggests the aerosol haze is based on photochemically produced hydrocarbons, similar to smog on Earth.

Scientists interpret the current atmospheric hydrogen in GJ 1132 b as hydrogen from the original atmosphere which was absorbed into the planet’s molten magna mantle and is now being slowly released through volcanic processes to form a new atmosphere. The atmosphere we see today is believed to be continually replenished to balance the hydrogen escaping into space.

GJ 1132 b is a super Earth exoplanet that orbits an M-type star. Its mass is 1.66 Earths, it takes 1.6 days to complete one orbit of its star, and is 0.0153 AU from its star. Its discovery was announced in 2015