Puffy planets lose atmospheres, become super-Earths
Astronomers have identified two different cases of"mini-Neptune" planets that are losing their puffy atmospheres and likely transforming into super-Earths. Radiation from the planets' stars is stripping away their atmospheres, driving hot gas to escape like steam from a pot of boiling water."Most astronomers suspected that young, small mini-Neptunes must have evaporating atmospheres," says Michael Zhang, lead author of both studies and a graduate student at Caltech.
In the new studies, a team of astronomers led by Caltech used Keck Observatory's Near-Infrared Spectrograph to study one of two mini-Neptune planets in the star system called TOI 560, located 103 light-years away; and they used Hubble to look at two mini-Neptunes orbiting HD 63433, located 73 light-years away.
"This was unexpected, as most models predict that the gas should flow away from the star," says Professor of Planetary Science Heather Knutson, Zhang's advisor and a co-author of the study."We still have a lot to learn about how these outflows work in practice."Since the first exoplanets orbiting Sun-like stars were discovered in the mid-1990s, thousands of others have been found.
Other scenarios could explain the gap, according to the astronomers. For instance, the smaller rocky planets might have never gathered gas envelopes in the first place, and mini-Neptunes could be water worlds and not enveloped in hydrogen gas. This latest discovery of two mini-Neptunes with escaping atmospheres represents the first direct evidence to support the theory that mini-Neptunes are indeed turning into super-Earths.
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