Ohmic Dissipation in the Interiors of Hot Jupiters
Abstract
We present models of ohmic heating in the interiors of hot Jupiters in which we decouple the interior and the wind zone by replacing the wind zone with a boundary temperature T iso and magnetic field B phi0. Ohmic heating influences the contraction of gas giants in two ways: by direct heating within the convection zone and by heating outside the convection zone, which increases the effective insulation of the interior. We calculate these effects and show that internal ohmic heating is only able to slow the contraction rate of a cooling gas giant once the planet reaches a critical value of internal entropy. We determine the age of the gas giant when ohmic heating becomes important as a function of mass, T iso, and induced B phi0. With this survey of parameter space complete, we then adopt the wind zone scalings of Menou and calculate the expected evolution of gas giants with different levels of irradiation. We find that, with this prescription of magnetic drag, it is difficult to inflate massive planets or those with strong irradiation using ohmic heating, meaning that we are unable to account for many of the observed hot Jupiter radii. This is in contrast to previous evolutionary models that assumed that a constant fraction of the irradiation is transformed into ohmic power.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- September 2012
- DOI:
- 10.1088/0004-637X/757/1/47
- arXiv:
- arXiv:1207.3278
- Bibcode:
- 2012ApJ...757...47H
- Keywords:
-
- magnetohydrodynamics: MHD;
- planets and satellites: atmospheres;
- planets and satellites: interiors;
- planets and satellites: magnetic fields;
- Astrophysics - Earth and Planetary Astrophysics
- E-Print:
- 14 pages, 17 figures. Submitted to ApJ