Mega-Earth found in Kepler-10c

The ‘Godzilla of Earths’ has been discovered by astronomers; the new type of planet is a mega-Earth; a rocky world weighing 17 times as much as Earth. It was believed a planet this large could not form because anything of this size would attract hydrogen gas as it grew and become a Jupiter-like gas giant. Kepler-10c, however, is solid and much bigger than previously discovered super-Earths. “We were very surprised when we realised what we had found,” said Xavier Dumusque from the Harvard-Smithsonian Center for Astrophysics (CfA). “This is the Godzilla of Earths!” added Dimitar Sasselov. “But unlike the movie monster, Kepler-10c has positive implications for life.” The planet orbits a sun-like star once every 45 days, and is located about 560 light-years from Earth in the Draco constellation. It has a diameter of about 18,000 miles – 2.3 times that of Earth – which meant astronomers thought it would be a mini-Neptune with a thick gaseous envelope. However, analysis using the HARPS-North Instrument on the Telescopio Nazionale Galileo in the Canary Islands revealed it weighs 17 times as much as Earth, suggesting a dense composition of rocks and other solids. “Kepler-10c didn’t lose its atmosphere over time. It’s massive enough to have held onto one if it ever had it,” said Dumusque. “It must have formed the way we see it now.” How large rocky worlds could develop has been difficult to explain, but CfA astronomer Lars A Buchhave has found a correlation between the period of a planet and the size at which a planet transitions from rocky to gaseous. This suggests more mega-Earths will be found as planet hunters extend their data to longer-period orbits. The discovery of Kepler-10c also has implications for the history of the universe and the possibility of life. The system is thought to be around 11 billion years old – so formed a mere 3 billion years after the Big Bang at a time when heavy elements were scare. “Finding Kepler-10c tells us that rocky planets could form much earlier than we thought,” said Sasselov. “And if you can make rocks you can make life.”