Habitable Evaporated Cores: Converting Mini-Neptunes into Super-Earths in the Habitable Zone of M Dwarfs
Abstract
We show that photoevaporation and Roche lobe overflow of small gaseous exoplanets (“mini-Neptunes”) in the habitable zone (HZ) of young late M dwarfs can remove several Earth masses of hydrogen/helium from these planets and transform them into potentially habitable worlds, which we call “habitable evaporated cores.” We couple a simple model for the evolution of inflated planets that are partly overflowing their Roche lobes with evaporation due to strong extreme ultraviolet (XUV) irradiation. We also couple the orbital effects of anisotropic mass loss with tidal evolution and show that this coupling can lead to unexpected behavior, such as a net increase of the eccentricity and an outward-then-inward evolution of the semi-major axis, significantly enhancing the mass loss rate. Habitable evaporated cores are most likely to form from planets with up to about 40% gas by mass orbiting M4 stars and later. As terrestrial planet formation by accumulation of local material is likely to form sub-Earth mass planets, evaporation of mini-Neptunes could be the dominant formation mechanism for volatile-rich super-Earths around M dwarfs. Such habitable evaporated cores are likely to be detected in upcoming surveys.
- Publication:
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American Astronomical Society Meeting Abstracts #223
- Pub Date:
- January 2014
- Bibcode:
- 2014AAS...22332505L