Planetary magnetic field control of ion escape from weakly magnetized planets

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Journal Title
Journal ISSN
Volume Title
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Date
2019-09
Major/Subject
Mcode
Degree programme
Language
en
Pages
2108-2120
Series
Monthly Notices of the Royal Astronomical Society, Volume 488, issue 2
Abstract
Intrinsic magnetic fields have long been thought to shield planets from atmospheric erosion via stellar winds; however, the influence of the plasma environment on atmospheric escape is complex. Here we study the influence of a weak intrinsic dipolar planetary magnetic field on the plasma environment and subsequent ion escape from a Mars-sized planet in a global three-dimensional hybrid simulation. We find that increasing the strength of a planet’s magnetic field enhances ion escape until the magnetic dipole’s standoff distance reaches the induced magnetosphere boundary. After this point increasing the planetary magnetic field begins to inhibit ion escape. This reflects a balance between shielding of the Southern hemisphere from ‘misaligned’ ion pickup forces and trapping of escaping ions by an equatorial plasmasphere. Thus, the planetary magnetic field associated with the peak ion escape rate is critically dependent on the stellar wind pressure. Where possible we have fit power laws for the variation of fundamental parameters (escape rate, escape power, polar cap opening angle, and effective interaction area) with magnetic field, and assessed upper and lower limits for the relationships.
Description
Keywords
plasmas, methods: numerical, planets and satellites: atmospheres, planets and satellites: magnetic fields
Other note
Citation
Egan, H, Järvinen, R, Ma, Y & Brain, D A 2019, ' Planetary magnetic field control of ion escape from weakly magnetized planets ', Monthly Notices of the Royal Astronomical Society, vol. 488, no. 2, pp. 2108-2120 . https://doi.org/10.1093/mnras/stz1819