Rocky super-Earths: variety in composition and energy budget

Abstract:

Solid exoplanets offer a unique opportunity for comparative planetology with the small solar system planets, and in particular with Earth. With more than 40 low-mass planets (with masses less than 10 earth-masses) with measured masses and radii, it is now possible to distinguish trends in the data. Although most of these planets have a substantial envelope that makes them closer in nature to Uranus and Neptune, there are about 10 low-mass exoplanets that are potentially rocky. Despite the uncertainties in the data (especially in the mass), it is becoming evident that there is variety in compositions expressed mostly in a wide range of Fe/Si ratios that may affect the interior dynamics and thermal evolution of these planets. In addition, numerous observing campaigns have targeted M stars to find super-Earths in the habitable zone, as this region is closer to the host star. It is well recognized that these planets may also be subjected to variable amounts of early and/or sustained tidal heating. This may in turn affect the mode of convection and outgassing of these planets. I will present results on the lessons learned from the super-Earth data and the implications of variable Fe/Si ratio and tidal heating for the dynamics of the interior using the model by [1] including a simple degassing model for water.

[1] Tackley, P. J., M. Ammann, J. P. Brodholt, D. P. Dobson and D. Valencia (2013) Mantle dynamics in super-Earths: Post-perovskite rheology and self-regulation of viscosity, Icarus 225(1), 50-61