Ohmic Dissipation in Mini-Neptunes
Abstract
In the presence of a magnetic field and weakly ionizing winds, ohmic dissipation is expected to take place in the envelopes of Jovian and lower-mass planets alike. While the process has been investigated on the former, there have been no studies done on mini-Neptunes so far. From structure and thermal evolution models, we determine that the required energy deposition for halting the contraction of mini-Neptunes increases with planetary mass and envelope fraction. Scaled to the insolation power, the ohmic heating needed is small: ∼ {10}-5 orders of magnitude lower than for exo-Jupiters ∼ {10}-2. Conversely, from solving the magnetic induction equation, we find that ohmic energy is dissipated more readily for lower-mass planets and those with larger envelope fractions. Combining these two trends, we find that ohmic dissipation in hot mini-Neptunes is strong enough to inflate their radii (∼ {10}15 W for {T}{eq}=1400 {{K}}). The implication is that the radii of hot mini-Neptunes may be attributed in part to ohmic heating. Thus, there is a trade-off between ohmic dissipation and H/He content for hot mini-Neptunes, adding a new degeneracy for the interpretation of the composition of such planets. In addition, ohmic dissipation would make mini-Neptunes more vulnerable to atmospheric evaporation.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- September 2017
- DOI:
- 10.3847/1538-4357/aa826f
- arXiv:
- arXiv:1709.01642
- Bibcode:
- 2017ApJ...846...47P
- Keywords:
-
- planets and satellites: composition;
- planets and satellites: interiors;
- planets and satellites: physical evolution;
- Astrophysics - Earth and Planetary Astrophysics
- E-Print:
- Published in ApJ