Is CoRoT-7 B the Remnant Core of an Evaporated Gas Giant?
Résumé
The recently discovered planet CoRoT-7 b has a density (5.7 g/cc) consistent with a rocky composition (Leger et al. 2009; Queloz et al. 2009). However, CoRoT-7 b's semi-major axis (0.0172 AU) suggests the planet has a history unlike the planets in our solar system. The strong stellar insolation received by CoRoT-7 b can quickly drive off an atmosphere and may have evaporated a few Earth masses of rocky material during the planet's lifetime. Such rapid mass loss even suggests that CoRoT-7 b may be the remnant core of a hot Jupiter whose gaseous envelope was completely evaporated. Also important are tides, which have drawn the planet in from a more distant, and possibly eccentric, orbit. As the planet neared its host star, the rate of mass loss probably increased dramatically, but mass loss slows tidal migration, resulting in a complex interplay between tides and mass loss. We combine tidal evolution and mass loss models to constrain the range of original orbits and masses of CoRoT-7 b and find, indeed, that CoRoT-7 b may once have been a gas giant planet. We discuss the plausible evolutionary pathways that allow CoRoT-7 b to have begun life as a gas giant. Our results suggest that similar processes may have influenced many other close-in exoplanets as well. Studying the coupled processes of mass loss and tidal migration may thus be crucial to unraveling the origins of the hundreds of hot super-Earths that may soon be discovered by the Kepler and CoRoT missions.