The Roles of Tidal Evolution and Evaporative Mass Loss in the Origin of CoRoT-7 b

TL;DR

This paper investigates how tidal evolution and evaporative mass loss have shaped CoRoT-7 b's current state, suggesting it may have started as a gas giant that lost its atmosphere and migrated inward due to star-planet interactions.

Contribution

It presents a coupled model of tidal decay and mass loss to explain the origin and evolution of CoRoT-7 b, highlighting the potential for significant orbital and mass changes.

Findings

Mass loss could have removed nearly half of the original planetary mass.

Tidal decay likely caused inward migration and orbital resonance interactions.

Original mass probably did not exceed 200 Earth masses.

Abstract

CoRoT-7 b is the first confirmed rocky exoplanet, but, with an orbital semi-major axis of 0.0172 AU, its origins may be unlike any rocky planet in our solar system. In this study, we consider the roles of tidal evolution and evaporative mass loss in CoRoT-7 b's history, which together have modified the planet's mass and orbit. If CoRoT-7 b has always been a rocky body, evaporation may have driven off almost half its original mass, but the mass loss may depend sensitively on the extent of tidal decay of its orbit. As tides caused CoRoT-7 b's orbit to decay, they brought the planet closer to its host star, thereby enhancing the mass loss rate. Such a large mass loss also suggests the possibility that CoRoT-7 b began as a gas giant planet and had its original atmosphere completely evaporated. In this case, we find that CoRoT-7 b's original mass probably didn't exceed 200 Earth masses (about 2/3 of a Jupiter mass). Tides raised on the host star by the planet may have significantly reduced the orbital semi-major axis, perhaps causing the planet to migrate through mean-motion resonances with the other planet in the system, CoRoT-7 c. The coupling between tidal evolution and mass loss may be important not only for CoRoT-7 b but also for other close-in exoplanets, and future studies of mass loss and orbital evolution may provide insight into the origin and fate of close-in planets, both rocky and gaseous.