Planetary magnetic field control of ion escape from weakly magnetized planets

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Planetary magnetic field control of ion escape from weakly magnetized planets. / Egan, Hilary; Järvinen, Riku; Ma, Y.; Brain, D. A.

In: Monthly Notices of the Royal Astronomical Society, Vol. 488, No. 2, 09.2019, p. 2108-2120.

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@article{0cad1e36831248aa83f845a77e8806c1,
title = "Planetary magnetic field control of ion escape from weakly magnetized planets",
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.",
keywords = "plasmas, methods: numerical, planets and satellites: atmospheres, planets and satellites: magnetic fields",
author = "Hilary Egan and Riku J{\"a}rvinen and Y. Ma and Brain, {D. A.}",
year = "2019",
month = "9",
doi = "10.1093/mnras/stz1819",
language = "English",
volume = "488",
pages = "2108--2120",
journal = "Monthly Notices of the Royal Astronomical Society",
issn = "0035-8711",
number = "2",

}

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TY - JOUR

T1 - Planetary magnetic field control of ion escape from weakly magnetized planets

AU - Egan, Hilary

AU - Järvinen, Riku

AU - Ma, Y.

AU - Brain, D. A.

PY - 2019/9

Y1 - 2019/9

N2 - 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.

AB - 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.

KW - plasmas

KW - methods: numerical

KW - planets and satellites: atmospheres

KW - planets and satellites: magnetic fields

UR - https://arxiv.org/abs/1907.02978

U2 - 10.1093/mnras/stz1819

DO - 10.1093/mnras/stz1819

M3 - Article

VL - 488

SP - 2108

EP - 2120

JO - Monthly Notices of the Royal Astronomical Society

JF - Monthly Notices of the Royal Astronomical Society

SN - 0035-8711

IS - 2

ER -

ID: 35590496