from the Super-Mega-Ultra dept.
Astronomers announced on June 2nd 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," making it a "mega-Earth."
The planet, Kepler-10c, orbits its host star every forty-five days at a quarter of the average distance between the Sun and Earth. It has a radius more than double that of Earth, but a higher density, making it the largest and most massive rocky planet discovered as of June 2014.
The story notes another aspect of Kepler-10c that complicates our understanding of planet formation:
The discovery that Kepler-10c is a mega-Earth 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.
So the question becomes how such a planet could have accumulated so much rocky material when so little was generally available at the time without also accumulating a large amount of gas and becoming a gas giant like Neptune and Jupiter.