Stars Strip Away the Atmosphere of Super-Earths

Even a super-Earth can fly too close to the sun, according to a new study from Yale University.

An international team of astronomers has found a new category of planets beyond our solar system whose atmosphere has been stripped bare by the radiation from their own sun. The findings will appear in the journal Nature Communications.

“It is as though they are standing very close to a blow-dryer set at maximum speed and heat,” said Yale astronomy professor Sarbani Basu, a co-author of the study. “All that is loose gets blown away. In this case it is the planet’s atmosphere.”

The study uses data from NASA’s Kepler mission to look at super-Earths, which are planets outside our solar system with a mass 1-10 times the mass of Earth. In particular, the researchers focused on super-Earths that receive more than 650 times the radiation from their host star that Earth receives from the Sun.

“This violent stripping occurs in planets that are made up of a rocky core with a gaseous out layer,” Basu said. “Due to the planets’ proximity to the star, the heat that they suffer means that their envelopes have been blown away by the intense radiation.”

The first author of the paper is Mia Lundkvist of Aarhus University in Denmark and Universität Heidelberg. Co-authors of the study represent more than a dozen other institutions in the United States, Australia, Denmark, and Germany.

The researchers said they used asteroseismology — which uses the natural resonances of stars to reveal their properties and inner structures — to characterize the host stars and their planets to levels of accuracy not achieved previously for these planetary systems. This, in turn, allowed the researchers to characterize the sizes of the extra-solar planets precisely.

“Our results have important implications for understanding how stellar systems, like our own solar system, and their planets evolve over time and the crucial role that the host star plays in the evolution of a planetary system,” Basu said.

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