Magnetospheric structure and atmospheric Joule heating of habitable planets orbiting M-dwarf stars

Journal Article · Sun Jul 20 00:00:00 EDT 2014 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/790/1/57· OSTI ID:22365565

Cohen, O.; Drake, J. J.; Garraffo, C.; Poppenhaeger, K. ^[1]; Glocer, A. ^[2]; Bell, J. M. ^[3]; Ridley, A. J.; Gombosi, T. I. ^[4]

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1. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
2. NASA/GSFC, Code 673, Greenbelt, MD 20771 (United States)
3. Center for Planetary Atmospheres and Flight Sciences, National Institute of Aerospace, Hampton, VA 23666 (United States)
4. Center for Space Environment Modeling, University of Michigan, 2455 Hayward Street, Ann Arbor, MI 48109 (United States)

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.

• OSTI ID: 22365565
• Journal Information: Astrophysical Journal, Vol. 790, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ALFVEN WAVES
BOUNDARY CONDITIONS
DENSITY
DWARF STARS
EXTREME ULTRAVIOLET RADIATION
HEATING RATE
JOULE HEATING
MAGNETIC FIELDS
MAGNETOHYDRODYNAMICS
ORBITS
PLANETARY IONOSPHERES
SATELLITE ATMOSPHERES
SATELLITES
SHOCK WAVES
SIMULATION
SPACE
STEADY-STATE CONDITIONS
STELLAR WINDS
TIME DEPENDENCE