Astronomers found the first exoplanet having the same mass as Earth, named KOI-314c. It is the lightest exoplanet ever found, whose the second lightest is Kepler-78b, with 1.7 times Earth's mass.

Located at 200 light-years from the Sun, KOI-314c has a surface temperature of 100°C orbits around its star in only 23 days. Its host star is less massive and cooler than the Sun. The planet has the same mass as Earth's, but is 1.6 times bigger than our planet.

The fact that the orbital period is only 23 days shows that the planet is close to the host star, and so it couldn't contain liquid water, and life. However, according to David Kipping from Harvard-Smithsonian Center for Astrophysics who is the main author of the discover, the exoplanet would have a very thick atmosphere containing hydrogen and helium. The beginning of its life could be the same as Neptune's, then the planet would have lost some of its atmospheric gases over time.

However, Kipping's team of astronomers who participated at HEK Project (Hunt for Exomoons with Kepler) thought that KOI-314c was in the beginning an exomoon orbiting around KOI-314b, an exoplanet having same size as KOI-314c but with 4 times Earth's mass, and orbiting around its host star in only 13 days. The team of astronomers saw then that KOI-314c was finally a planet and not an exomoon.

Sources : Sciences et Avenir (french) and Slate.com

Read also : Exomoon research could start at 1800 light-years from the Sun