  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.
