A space rock collision may explain how this exoplanet was born


Cataclysmic collisions between space rocks have helped explain some of the solar system’s biggest mysteries, from how the moon formed to how Uranus got its lopsided rotation. But convincing evidence for such events happening outside of the solar system is scant.

Now scientists think that they have found the first known example of a near head-on collision between two massive worlds in another planetary system, roughly 2,000 light-years away from Earth.

The chance discovery came while researchers were observing Kepler 107, a sunlike star with four orbiting planets first described in 2014, to determine each planet’s mass. Surprisingly, the star’s two innermost planets, each roughly 1.5 times the size of Earth, have dramatically different masses, the team reports February 4 in Nature Astronomy. Analysis of each planet’s mass and size revealed that Kepler 107c is roughly twice as dense as Kepler 107b. That finding suggests that Kepler 107c has a large iron-rich core, similar to the solar system’s innermost planet, Mercury, the scientists say.