Yanqin Wu, Yoram Lithwick
We study the radius evolution of close-in extra-solar jupiters under Ohmic
heating, a mechanism that was recently proposed to explain the large observed
sizes of many of these planets. Planets are born with high entropy and they
subsequently cool and contract. We focus on two cases: first, that ohmic
heating commences when the planet is hot (high entropy); and second, that it
commences after the planet has cooled. In the former case, we use analytical
scalings and numerical experiments to confirm that Ohmic heating is capable of
suspending the cooling as long as a few percent of the stellar irradiation is
converted into Ohmic heating, and the planet has a surface wind that extends to
pressures of ~10 bar or deeper. For these parameters, the radii at which
cooling is stalled are consistent with (or larger than) the observed radii of
most planets. The only two exceptions are WASP-17b and HAT-P-32b. In contrast
to the high entropy case, we show that Ohmic heating cannot significantly
re-inflate planets after they have already cooled. This leads us to suggest
that the diversity of radii observed in hot jupiters may be partially explained
by the different epochs at which they are migrated to their current locations.
View original:
http://arxiv.org/abs/1202.0026
No comments:
Post a Comment