Efficient and inefficient hydrodynamic escape of exo-satellite atmospheres driven by irradiation from their young giant planets
File(s)staf490.pdf (3.7 MB)
Published version
Author(s)
Schulik, Matthäus
Owen, James E
Booth, Richard A
Ling, Shun Fai
Wong, Shun Ping
Type
Journal Article
Abstract
The bolometric radiation from a central body is potentially a powerful driver of atmospheric escape from planets or satellites. When heated above their equilibrium temperatures those satellites, due to their low surface gravity, are be prone to significant atmospheric erosion. Such high temperatures can be reached through a known mechanism: a large ratio of the irradiation to re-radiation opacities of the atmospheric species. We investigate this mechanism for irradiating black-bodies of sub-stellar temperatures and find that specific molecules exist, such as $\rm NH_3$ and $\rm CH_4$, which develop temperature inversions under the irradiation of young post-formation giant planets. These non-isothermal temperature profiles lead to escape rates that can significantly exceed isothermal Parker-model escape rates evaluated at the satellite’s equilibrium temperature. Our results indicate that exo-satellites can lose most of their atmospheric mass through this mechanism if the cooling of the exo-satellite’s interior is not too rapid. In all scenarios, we find a hierarchical ordering of escape rates of atmospheric species due to thermal decoupling in the upper atmosphere. This thermal decoupling leads to a natural depletion of $\rm CH_4$ and retention of $\rm NH_3$ in our models. We find that giant planets with masses above 2$m_{\rm Jup}$, for cold starts and above 1$m_{\rm Jup}$ in hot start scenarios are able to remove the majority of a Titan analogue’s atmosphere. Hence, finding and characterizing exomoon atmospheres in hypothetical future surveys can constrain the post-formation cooling behaviour of giant planets.
Date Issued
2025-05-01
Date Acceptance
2025-03-20
Citation
Monthly Notices of the Royal Astronomical Society, 2025, 539 (3), pp.2121-2143
ISSN
0035-8711
Publisher
Oxford University Press (OUP)
Start Page
2121
End Page
2143
Journal / Book Title
Monthly Notices of the Royal Astronomical Society
Volume
539
Issue
3
Copyright Statement
© 2025 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.
License URL
Identifier
10.1093/mnras/staf490
Subjects
hydrodynamics -planets and satellites
atmospheres -planets and satellites
gaseous planets
Publication Status
Published
Date Publish Online
2025-03-26