The first gases to be identified around an exoplanet that is slightly larger than Earth show that its atmosphere is probably rich in hydrogen and carbon.

Angelos Tsiaras of University College London and his colleagues used a camera on the Hubble Space Telescope to probe the planet 55 Cancri e, which has a radius twice that of Earth, lies 12 parsecs (about 40 light years) away and orbits close to its host star.

The team found that the planet's atmosphere contains no water vapour but does have hydrogen, probably in the form of hydrogen cyanide, which is an indicator of carbon-rich atmospheres. The high level of carbon suggests exotic chemistry around the planet.

Astrophys. J. in the press; preprint at (2016)