Role of Planetary Obliquity in Regulating Atmospheric Escape: G-dwarf vs. M-dwarf Earth-like Exoplanets

Logarithmic scale contour plots of the O+ ion density with magnetic field lines (in white) in the meridional plane based on the stellar wind conditions at current Earth (top two rows) and at TRAPPIST-1g (bottom two rows). Different plots correspond to various choices of the planetary magnetic obliquity. Note the same colorbar range but the different box size between the top two rows and the bottom two rows.

We present a three-species multi-fluid MHD model (H+, O+ and e−), endowed with the requisite upper atmospheric chemistry, that is capable of accurately quantifying the magnitude of oxygen ion losses from "Earth-like" exoplanets in habitable zones, whose magnetic and rotational axes are roughly coincidental with one another.

We apply this model to investigate the role of planetary obliquity in regulating atmospheric losses from a magnetic perspective. For Earth-like exoplanets orbiting solar-type stars, we demonstrate that the dependence of the total atmospheric ion loss rate on the planetary (magnetic) obliquity is relatively weak; the escape rates are found to vary between 2.19×1026 s−1 to 2.37×1026 s−1. In contrast, the obliquity can influence the atmospheric escape rate (∼ 1028 s−1) by more than a factor of 2 (or 200%) in the case of Earth-like exoplanets orbiting late-type M-dwarfs. Thus, our simulations indicate that planetary obliquity may play a weak-to-moderate role insofar as the retention of an atmosphere (necessary for surface habitability) is concerned.

Chuanfei Dong, Zhenguang Huang, Manasvi Lingam
(Submitted on 17 Jul 2019)

Comments: 9 pages, 3 figures and 2 tables
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR); Space Physics (physics.space-ph)
Cite as: arXiv:1907.07459 [astro-ph.EP] (or arXiv:1907.07459v1 [astro-ph.EP] for this version)
Submission history
From: Chuanfei Dong
[v1] Wed, 17 Jul 2019 11:53:37 UTC (3,498 KB)
https://arxiv.org/abs/1907.07459
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