CoRoT-7 b: Super-Earth or Super-Io?
Résumé
CoRoT-7 b, a planet about 70% larger than the Earth orbiting a Sun-like star, is the first-discovered rocky exoplanet, and hence has been dubbed a "super-Earth". Initial studies indicate that the planet receives enough insolation to partially melt its surface. However, tides also contribute significantly to the heat budget in several ways. Even if there has never been direct tidal heating (e.g. if the planet's eccentricity has always been zero), orbital decay by tides may have very recently placed the planet in an orbit in which its insolation could melt silicates. On the other hand, CoRoT-7 b could be tidally heated at a rate that dominates its geophysics and drives extreme volcanism, making it a "super-Io" similar to Jupiter's volcanic moon. Such heating could occur with an eccentricity of just 10-5. Although this value is very small, the tidal damping of eccentricity is extreme due to the very small orbit. We have considered various mechanisms for maintaining a non-zero eccentricity, but only perturbations from CoRoT-7 c can raise b's eccentricity large enough to induce Io-like heating, and only if its eccentricity is of order 10-4. Such a value is plausible, though below current detection thresholds. Nonetheless, CoRoT-7 b may be the first of a class of planetary super-Ios likely to be revealed by the CoRoT and Kepler spacecraft.