Protostars and Planets VI, Heidelberg, July 15-20, 2013

Poster 2K064


Kurokawa, Hiroyuki (Nagoya University)
Nakamoto, Taishi (Tokyo Institute of Technology)

Close-in exoplanets might have lost substantial masses during their evolution due to atmospheric escape of upper atmosphere heated by intense stellar XUV (X-ray and EUV) radiation and dynamical Roche-lobe overflow. We focus on its effects on population and composition of exoplanets. We develop a numerical model to simulate an evolution of planets considering thermal cooling and the mass-loss. An semi-analytical model of the radiation-recombination limited escape is developed and included in the model, as well as the energy-limited escape. The Roche-lobe overflow is also taken into account as a mass-loss process. The model is applied to the mass-loss of Hot-Jupiters and low-density Super-Earths which have envelopes of hydrogen and helium. First, basic properties of the mass-loss evolution are described using envelope mass - planetary radius relationships which combine Jupiter mass regime with Super-Earth regime. A runaway property of the mass-loss evolution is shown in the relation diagrams. The relation also indicates the possibility of Roche-lobe overflow at sub-Jupiter mass regime regime for close-in exoplanets. Second, evaporation of Hot-Jupiters is studied and compared with population of exoplanets. Effects of core mass and migration history are considered. The migration history does not affect the results, but the effect of the core mass is significant. The sub-Jupiter desert at close-in obit can be produced by the evaporation of Hot-Jupiters having small cores. Third, Our model is applied to the mass-loss of low-density Super-Earths. The results are consistent with the observed distribution of low-density Super-Earths: gas-rich Super-Earths have relatively distant orbits and large mass. Also we constrain the compositions of low-density Super-Earths whose compositions are not constrained only from mass-radius relationships.

Click here to view poster PDF