Simulation of a collision between two exoplanets

A 3D simulation shows the impact of two planets. Grey represents the coolest temperatures, red the hottest. Credit: Zoë M. Leinhardt and Thomas Denman/Univ. Bristol

Planetary science

Giant impact might have shaped a distant world

A smash-up in space could underlie the origins of an odd exoplanet couple.

A cosmic collision might have caused the difference between two exoplanets that circle the same star.

Astronomers know of four planets orbiting the star Kepler-107, which lies in the constellation Cygnus. The two innermost planets, Kepler-107b and Kepler-107c, are both about 1.5 times the diameter of the Earth — but their densities are very different, according to a team led by Aldo Bonomo of the National Institute for Astrophysics in Pino Torinese, Italy.

Using a telescope in the Canary Islands, the scientists tracked changes in Kepler-107’s light as the planets’ gravity tugged on the star. According to the team’s calculations, Kepler-107c is more than twice as dense as its similarly sized neighbor. The scientists propose that Kepler-107c was once much larger, but a catastrophic collision with an unknown object stripped off some of the planet’s outer layers and left mostly an iron-rich core.

If confirmed, this discovery would constitute the first evidence of a giant impact in a world beyond the Solar System.