Hubble finds first evidence of volcanic activity reforming exoplanet atmosphere

Scientists using the Hubble Space Telescope have found the first evidence of volcanic activity reforming the atmosphere on a rocky planet around a distant star.

The planet GJ 1132 b, which has a similar density, size and age to Earth, seems to have begun life as a gaseous world - a so-called ‘sub-Neptune’.

But its primordial hydrogen and helium atmosphere was stripped away by intense radiation from its hot, young star. It was reduced to a core about the size of Earth.

Hubble observations have now found a secondary atmosphere that has replaced the planet’s first atmosphere, which is rich in hydrogen, hydrogen cyanide, methane and ammonia, and also has a hydrocarbon haze.

Astronomers suggest that hydrogen from the original atmosphere was absorbed into the planet’s molten magma mantle and is now being slowly released by volcanism to form a new atmosphere.

Paul Rimmer, of the Department of Earth Sciences and the Cavendish Laboratory at the University of Cambridge, and the MRC Laboratory of Molecular Biology in Cambridge, said: “This second atmosphere comes from the surface and interior of the planet, and so it is a window onto the geology of another world. A lot more work needs to be done to properly look through it, but the discovery of this window is of great importance.

“It gives exoplanet scientists a way to figure out something about a planet's geology from its atmosphere.

“It is also important for understanding where the rocky planets in our own Solar System — Mercury, Venus, Earth and Mars, fit into the bigger picture of comparative planetology, in terms of the availability of hydrogen versus oxygen in the atmosphere.”

Team member Raissa Estrela, of the Jet Propulsion Laboratory at the California Institute of Technology in Pasadena, California, USA, added: “We first thought that these highly radiated planets would be pretty boring because we believed that they lost their atmosphere. But we looked at existing observations of this planet with Hubble and realised that there is an atmosphere there.”

Team leader Mark Swain, of the Jet Propulsion Laboratory, said: “How many terrestrial planets don’t begin as terrestrials? Some may start as sub-Neptunes, and they become terrestrials through a mechanism whereby light 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 that 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.”

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