A new study lets some of the air out of a long-held theory that growing, rocky planets will lose their atmosphere if they smash into a large object in space.
In fact, these kinds of collisions often help proto-planets hold onto their hydrogen-rich primordial atmosphere, say researchers Jun Korenaga of Yale and Darius Modirrousta-Galian, a former Yale postdoc who is now at Shanghai Jiao Tong University.
"Giant impacts are a key part of how rocky planets grow," said Korenaga, a professor of Earth and planetary sciences in Yale's Faculty of Arts and Sciences and co-author of the new study in the journal Nature Astronomy.
"Planets the size of Earth or larger are expected to form through collisions between smaller planetary bodies," Korenaga said. "These collisions add mass and release enormous amounts of heat, which can drive atmospheric escape. Their effect on a planet's atmosphere depends on how those two changes work together."
The new research also sheds light on the predominance of two types of planets beyond Earth's solar system: "super-Earths," exoplanets that are slightly larger than Earth and have no primordial atmosphere, and "sub-Neptunes," which are even larger and do have a primordial atmosphere.
"Why nature produces both types in such abundance is a fundamental puzzle in exoplanetary science," said Modirrousta-Galian, a former postdoctoral researcher in Korenaga's lab and lead author of the study. "We set out to find an explanation."
Over the past few years, Modirrousta-Galian and Korenaga have written a series of papers laying out the foundation for how atmospheric escape and planetary interiors should co-evolve. The new study brings these studies together to conceptualize what happens after a giant collision.
