Rooting around extrasolar planetary systems like paleontologists on a dinosaur dig astronomers have found a remarkable new planet 17 times more massive than Earth. Improbably, it’s made of rock.
Planets that huge should have grabbed the hydrogen gas in their neighborhood to become big gas bags like Jupiter and Saturn. Not this one. It’s all solids and much bigger than previous “super Earth” finds. Like our paleontologist friends, it’s time to add a new entry to the ever-growing list of planet species.
Kepler-10c circles a sunlike star once every 45 days. It is located about 560 light-years from Earth in the constellation Draco. The system also hosts the ‘lava world’ Kepler-10b, which circles so close to its host star the molten planet zips around it every 20 days.
Normally planets this massive are more like the planet Neptune with its gassy cloak of hydrogen and helium tinted blue by the addition of methane. 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.
To distinguish whether its heavy mass came from gas or solids, a team of astronomers from the team of astronomers from the Harvard-Smithsonian Center for Astrophysics used the HARPS-North instrument on the Telescopio Nazionale Galileo in the Canary Islands to measure the mass of Kepler-10c. (HARPS stands for High-Accuracy Radial velocity Planet Searcher) This precision spectrograph is designed to detect the tiny changes in speed induced by planets as small as Earth on their host stars, so long as they orbit close to that star.
They found that Kepler-10c weighed 17 times as much as Earth, much more than expected for a gaseous Neptune-like planet. From this, the team inferred that Kepler-10c must have a dense composition of rocks and other solids. The discovery also has profound implications for the possibility of life arising in the universe long ago. The Kepler-10 system is about 11 billion years old, which means it formed fewer than 3 billion years after the Big Bang.
Rocky planets are made of heavy elements like iron, magnesium and silicon, materials that have to be manufactured in the cores of stars and then released into space through supernova explosions. But the early universe was basically all hydrogen and helium. 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.
Rocks and life – I hadn’t thought how much we had in common but it’s true. Both are built of complex elements. Salt of the Earth. Dust blowin’ in the wind. These are the very things that keep us humming along generation after generation.
Kepler-10c not only expands our idea of what makes a planet, but the fact that it’s out there at all implies that older star systems can no longer be dismissed as places to search for habitable worlds.