A new Yale co-authored paper reveals a phenomenon through which the atmosphere of planets is stripped away by radiation from the stars they orbit.
The research, published last Monday in the journal Nature Communications, uncovers new information about “super-Earths,” planets two to 10 times the size of Earth. These planets orbit stars far enough away that collecting data on them proves difficult, especially as many of these super-Earths do not appear on conventional astronomical graphs. The researchers identified photoevaporation, the process through which the atmosphere of a planet is stripped away by radiation from the star it orbits, as the cause of the conspicuous absence of these planets.
“These planets can’t withstand the radiation pressure from the star, so the gases from the planets are stripped away,” astronomy professor and study co-author Sarbani Basu said. “As a result, we are left with this hole in the graph where we expect to see these larger planets.”
The project began when Mia Lundkvist and her supervisor Hans Kjeldsen, both researchers at Aarhus University in Denmark, began studying periodic changes in brightness in stars with orbiting planets. After plotting the data, they noticed that there were fewer hot super-Earths present in the diagram than they had anticipated, Lundkvist said. She decided to research why these super-Earths were not visible in the data. The researchers ultimately determined that predicted effects of photoevaporation matched the measurements of the practical “invisibility” of these planets, many of which receive more than 600 times the amount of radiation than Earth.
According to the study, the researchers used data from the Kepler spacecraft to perform their analysis. They were able to use the data about stars to find out more about the smaller non-light-emitting planets that orbit them. They used a technique known as asteroseismology, a means of analyzing stars to understand both the internal structures of stars themselves and the effects those stars have on their exoplanets, according to Guy Davies, research fellow at the University of Birmingham and co-author of the paper.
“Just like seismologists study properties of what’s happening inside the earth using earthquake data, we study properties of stars using starquake data,” Basu said.
While other researchers have put forth theories and predictions regarding photoevaporation, this study narrowed research down to an unprecedented degree of precision, Davies said. All researchers agreed that the data has demonstrated that photoevaporation is a phenomenon that can further clarify models of planetary evolution.
After the sun, the closest star to Earth is a triple-star system, Alpha Centauri, which consists of three stars bound together by gravity.