News Astronomy

Rocky, overweight planet shakes up theories

Distant exoplanet is as massive as Neptune but has a composition closer to Earth's

PLUMP PLANET  Kepler-10c, a rocky planet 17 times as massive as Earth, orbits its sun in an artist’s illustration. Its sister planet, Kepler-10b, is in the background, sitting much closer to the star.

David A. Aguilar/CfA

By Christopher Crockett

- More than 2 years ago

BOSTON — Common wisdom in astronomy says that once a planet has collected about 10 Earths’ worth of rock, it becomes a gas giant like Neptune or Saturn.