Two Mini-Neptunes Lose Their Puffy Atmospheres, Transform into Super-Earth Exoplanets astronomy space science
An artist’s impression of a mini-Neptune exoplanet and its parent star. Image credit: Adam Makarenko, Keck Observatory.These worlds are thought to consist of large rocky cores surrounded by thick atmospheres.
“Most astronomers suspected that young, mini-Neptunes must have evaporating atmospheres. But nobody had ever caught one in the process of doing so until now,” said Dr. Michael Zhang, graduate student at Caltech.HD 63433They also used the Near-Infrared Echelle Spectrograph on the Keck II Telescope at the W.M.
“This was unexpected, as most models predict that the gas should flow away from the star,” said Caltech Professor Heather Knutson.The astronomers were able to detect the escaping atmospheres by watching the mini-Neptunes cross in front of, or transit, their stars. In the case of TOI-560b, they found signatures of helium. For HD 63433, they found signatures of hydrogen in HD 63433c, but not the inner planet, HD 63433b.“The speed of the gases provides the evidence that the atmospheres are escaping.”
“The observed helium around TOI-560b is moving as fast as 20 km/sec, while the hydrogen around HD 63433c is moving as fast as 50 km/sec.”“The extent of the outflows around the planets also indicates escaping atmospheres; the cocoon of gas around TOI-560b is at least 3.5 times as large as the radius of the planet, and the cocoon around HD 63433c is at least 12 times the radius of the planet.
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