Magnetospheric Structure and Atmospheric Joule Heating of Habitable Planets Orbiting M-dwarf Stars

O. Cohen, J. J. Drake, A. Glocer, C. Garraffo, K. Poppenhaeger, J. M. Bell, A. J. Ridley, T. I. Gombosi

Research output: Contribution to journalArticle

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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 languageEnglish
Article number57
Number of pages13
JournalThe Astrophysical Journal
Volume790
Issue number1
Early online date03 Jul 2014
DOIs
Publication statusPublished - 20 Jul 2014

Fingerprint

atmospheric heating
dwarf stars
M stars
Joule heating
planets
planet
ionospherics
heating
sectors
stellar winds
bows
planetary ionospheres
shock
planetary magnetospheres
planetary orbits
atmospheres
atmospheric particle
atmosphere
radiation
atmospheric pressure

Keywords

  • magnetohydrodynamics: MHD
  • planets and satellites: atmospheres
  • planets and satellites: magnetic fields
  • planets and satellites: terrestrial planets

Cite this

Cohen, O., Drake, J. J., Glocer, A., Garraffo, C., Poppenhaeger, K., Bell, J. M., ... Gombosi, T. I. (2014). Magnetospheric Structure and Atmospheric Joule Heating of Habitable Planets Orbiting M-dwarf Stars. The Astrophysical Journal, 790(1), [57]. https://doi.org/10.1088/0004-637X/790/1/57
Cohen, O. ; Drake, J. J. ; Glocer, A. ; Garraffo, C. ; Poppenhaeger, K. ; Bell, J. M. ; Ridley, A. J. ; Gombosi, T. I. / Magnetospheric Structure and Atmospheric Joule Heating of Habitable Planets Orbiting M-dwarf Stars. In: The Astrophysical Journal. 2014 ; Vol. 790, No. 1.
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Cohen, O, Drake, JJ, Glocer, A, Garraffo, C, Poppenhaeger, K, Bell, JM, Ridley, AJ & Gombosi, TI 2014, 'Magnetospheric Structure and Atmospheric Joule Heating of Habitable Planets Orbiting M-dwarf Stars', The Astrophysical Journal, vol. 790, no. 1, 57. https://doi.org/10.1088/0004-637X/790/1/57

Magnetospheric Structure and Atmospheric Joule Heating of Habitable Planets Orbiting M-dwarf Stars. / Cohen, O.; Drake, J. J.; Glocer, A.; Garraffo, C.; Poppenhaeger, K.; Bell, J. M.; Ridley, A. J.; Gombosi, T. I.

In: The Astrophysical Journal, Vol. 790, No. 1, 57, 20.07.2014.

Research output: Contribution to journalArticle

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T1 - Magnetospheric Structure and Atmospheric Joule Heating of Habitable Planets Orbiting M-dwarf Stars

AU - Cohen, O.

AU - Drake, J. J.

AU - Glocer, A.

AU - Garraffo, C.

AU - Poppenhaeger, K.

AU - Bell, J. M.

AU - Ridley, A. J.

AU - Gombosi, T. I.

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N2 - 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.

AB - 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.

KW - magnetohydrodynamics: MHD

KW - planets and satellites: atmospheres

KW - planets and satellites: magnetic fields

KW - planets and satellites: terrestrial planets

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DO - 10.1088/0004-637X/790/1/57

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VL - 790

JO - The Astrophysical Journal

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SN - 0004-637X

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