Feb. 6 (UPI) -- Scientists have for the first time discovered evidence of a planetary collision outside the solar system. Astronomers discovered evidence of the exoplanet mashup inside the Kepler 107 system.
At least four planets orbit the spectral type G2 star known as Kepler 107. According to a new paper published in the journal Nature Astronomy, at least two of those planets were produced by a celestial collision.
To more accurately characterize the orbital trajectories of the four Kepler 107 planets, astronomers combined data from Kepler, the retired planet-hunting space observatory, and the National Galileo Telescope at the Roque de los Muchachos Observatory on the Canary Islands.
Astronomers were most interested in the two innermost planets. Though their radii are the same, the second planet is three time denser than the planet closest to its sun.
It's unusual for such a large planet to be so massive. The surprisingly high density of Kepler 107c suggests the planet boasts a metallic core.
Theories of planetary evolution predict the main way planets change size and mass is by losing their outer layers, which are evaporated by the radiation from their host star. As lighter outer layers are lost, the planet becomes denser.
If evaporation was the main force shaping the evolution of planets around Kepler 107b, then the closest planet to the G2 star should be the densest. It is not.
The other way planets evolve is through sizable collisions. To see if a planetary mashup could explain Kepler 107's unusual planetary arrangement, astronomers built a variety of simulations. Their model showed a large collision was the best explanation for the second planet's loss of its outer layers.
"The dissimilar densities are consistent with a giant impact event on Kepler-107c that would have stripped off part of its silicate mantle," scientists wrote in their paper.
As part of the analysis of Kepler 107, researchers used new analysis techniques to more accurately determine the characterized the effects of stellar physics on planetary evolution.
"We need to know the star to better understand the planets which are in orbit around it," Savita Mathur, a researcher at the Institute of Astrophysics of the Canary Islands, said in a news release. "In this study we made a seismic analysis to estimate the parameters of the star which hosts the planet. Asteroseismology is playing a key role in the field of the exoplanets, because it has been shown that it is one of the best methods for a precise characterization of the stars."