Exoplanets & Exomoons

Role Of Planetary Radius on Atmospheric Escape of Rocky Exoplanets

By Keith Cowing
Status Report
January 31, 2024
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Role Of Planetary Radius on Atmospheric Escape of Rocky Exoplanets
Logarithmic scale contour plots of the escaping O+ ion density (units of cm−3 ) in the meridional plane for cases with different planetary radii subjected to the same ancient solar conditions. The second plot from the left in the top row (R = 0.75 RV ) has the highest atmospheric ion escape rate. — astro-ph.EP

Large-scale characterization of exoplanetary atmospheres is on the horizon, thereby making it possible in the future to extract their statistical properties.

In this context, by using a well validated model in the solar system, we carry out three-dimensional magnetohydrodynamic simulations to compute nonthermal atmospheric ion escape rates of unmagnetized rocky exoplanets as a function of their radius based on fixed stellar radiation and wind conditions. We find that the atmospheric escape rate is, unexpectedly and strikingly, a nonmonotonic function of the planetary radius R and that it evinces a maximum at R∼0.7R⊕.

This novel nonmonotonic behavior may arise from an intricate tradeoff between the cross-sectional area of a planet (which increases with size, boosting escape rates) and its associated escape velocity (which also increases with size, but diminishes escape rates). Our results could guide forthcoming observations because worlds with certain values of R (such as R∼0.7R⊕) might exhibit comparatively higher escape rates when all other factors are constant.

Laura Chin, Chuanfei Dong, Manasvi Lingam

Comments: 7 pages, 2 figures, 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:2401.16211 [astro-ph.EP] (or arXiv:2401.16211v1 [astro-ph.EP] for this version)
Submission history
From: Chuanfei Dong
[v1] Mon, 29 Jan 2024 15:04:08 UTC (441 KB)

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻