Planetary magnetic field control of ion escape from weakly magnetized planets

Hilary Egan, Riku Järvinen, Y. Ma, D. A. Brain

Research output: Contribution to journalArticleScientificpeer-review

19 Citations (Scopus)
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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.
Original languageEnglish
Pages (from-to)2108-2120
JournalMonthly Notices of the Royal Astronomical Society
Issue number2
Publication statusPublished - Sep 2019
MoE publication typeA1 Journal article-refereed


  • plasmas
  • methods: numerical
  • planets and satellites: atmospheres
  • planets and satellites: magnetic fields


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