A comparative study of atmospheric escape in the brightest system of super-earths straddling the evaporation valley
Abstract
Photo-evaporation of planetary atmospheres plays a key role in the evolution of exoplanets, carving their whole population. However, direct observations of atmospheric escape are scarce and almost non-existent in the mass range of super-Earths and mini-Neptunes, while these planets are among the most impacted by the phenomenon. A huge step forward could be made by achieving a comparative study of several super-Earths, volatile-rich or not, in a single multi-planet system: such planets would indeed experience the same evolution of the stellar X and EUV flux that are driving atmospheric escape. The perfect system for such a study has just been identified: the nearby, solar-type, and naked-eye star nu^2 Lupi hosts transiting planets spanning a remarkably large range of insolation (~100 to ~5x the insolation of Earth). TESS found the transits of the two inner planets and CHEOPS detected the transit of planet d, a volatile-rich super-Earth with an exceptional period of 107 day. These super-Earths straddle the radius gap of the "evaporation valley" and could have retained different fractions of gas and volatiles. Like for previously observed warm Neptunes, they could be enshrouded in huge comet-like exospheric clouds of escaping gas, which could have built up in the mild radiative environment. The system unique combination of proximity, brightness and favorable planet characteristics offers a fantastic opportunity to exploit HST ultraviolet capabilities to search for the hydrogen, oxygen and carbon escaping three planets in whole new mass and irradiation regimes. It is the ideal testbed for advancing both observations and theories of atmospheric evaporation of exoplanets.
- Publication:
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HST Proposal
- Pub Date:
- June 2022
- Bibcode:
- 2022hst..prop16998E