Abstract
We study the magnetospheric structure and the ionospheric Joule Heating
of planets orbiting M-dwarf stars in the habitable zone using a set of
magnetohydrodynamic models. The stellar wind solution is used to drive a
model for the planetary magnetosphere, which is coupled with a model for
the planetary ionosphere. Our simulations reveal that the space
environment around close-in habitable planets is extreme, and the
stellar wind plasma conditions change from sub- to super-Alfvénic
along the planetary orbit. As a result, the magnetospheric structure
changes dramatically with a bow shock forming in the
super-Alfvénic sectors, while no bow shock forms in the
sub-Alfvénic sectors. The planets reside most of the time in the
sub-Alfvénic sectors with poor atmospheric protection. A
significant amount of Joule Heating is provided at the top of the
atmosphere as a result of the intense stellar wind. For the steady-state
solution, the heating is about 0.1%-3% of the total incoming stellar
irradiation, and it is enhanced by 50% for the time-dependent case. The
significant Joule Heating obtained here should be considered in models
for the atmospheres of habitable planets in terms of the thickness of
the atmosphere, the top-side temperature and density, the boundary
conditions for the atmospheric pressure, and particle radiation and
transport. Here we assume constant ionospheric Pedersen conductance
similar to that of the Earth. The conductance could be greater due to
the intense EUV radiation leading to smaller heating rates. We plan to
quantify the ionospheric conductance in future study.
| Original language | English |
|---|---|
| Article number | 57 |
| Number of pages | 13 |
| Journal | The Astrophysical Journal |
| Volume | 790 |
| Issue number | 1 |
| Early online date | 03 Jul 2014 |
| DOIs | |
| Publication status | Published - 20 Jul 2014 |
Keywords
- magnetohydrodynamics: MHD
- planets and satellites: atmospheres
- planets and satellites: magnetic fields
- planets and satellites: terrestrial planets