Kepler-10c dominates the foreground in this artist’s conception. Its sibling, the lava world Kepler-10b, is in the background. Both orbit a sunlike star. Kepler-10c has a diameter of about 18,000 miles, 2.3 times as large as Earth, and weighs 17 times as much. Therefore it is all solids, although it may possess a thin atmosphere shown here as wispy clouds. Credit: David A. Aguilar, Harvard Smithsonian Center for Astrophysics.

(NASA) – At the Meeting of the American Astronomical Society (AAS) a team of astronomers from Harvard-Smithsonian Center for Astrophysics (CfA) announced that they have discovered a new type of planet – a rocky world weighing 17 times as much as Earth. Theorists believed such a world couldn’t form because anything so hefty would grab hydrogen gas as it grew and become a Jupiter-like gas giant. This planet, though, is all solids and much bigger than previously discovered “super-Earths” …Kepler-10c circles a sunlike star once every 45 days. It is located about 560 light-years from Earth in the constellation Draco. …Kepler-10c was originally spotted by NASA’s Kepler spacecraft … using the transit method, looking for a star that dims when a planet passes in front of it. …Kepler-10c was known to have a diameter of about 18,000 miles, 2.3 times as large as Earth. This suggested it fell into a category of planets known as mini-Neptunes, which have thick, gaseous envelopes.

The [CfA team] found that it weighed 17 times as much as Earth – far more than expected. This showed that Kepler-10c must have a dense composition of rocks and other solids. …The discovery…also has profound implications for the history of the universe and the possibility of life. The Kepler-10 system is about 11 billion years old, which means it formed less than 3 billion years after the Big Bang. The early universe contained only hydrogen and helium. Heavier elements needed to make rocky planets, like silicon and iron, had to be created in the first generations of stars. When those stars exploded, they scattered these crucial ingredients through space, which then could be incorporated into later generations of stars and planets. This process should have taken billions of years. However, Kepler-10c shows that the universe was able to form such huge rocks even during the time when heavy elements were scarce.

“Finding Kepler-10c tells us that rocky planets could form much earlier than we thought. And if you can make rocks, you can make life,” says CfA researcher Dimitar Sasselov, director of the Harvard Origins of Life Initiative. This research implies that astronomers shouldn’t rule out old stars when they search for Earth-like planets. And if old stars can host rocky Earths too, then we have a better chance of locating potentially habitable worlds in our cosmic neighborhood.

• Press Release from Harvard Smithsonian Center for Astrophysics