[astro-ph.EP] The ranks of accreting planets and brown dwarfs are growing. To help interpret their spectra, we study how accretion affects a planet’s atmosphere. The atmosphere is irradiated from above by whatever nonthermal radiation from the accretion shock does not directly escape into space.
This accretional heating drives a temperature inversion. Even relatively slow accretion, corresponding to mass doubling times longer than system ages, can raise temperatures by many hundreds of Kelvin at ambient pressures of order millibars. The heated atmosphere radiates an optical/infrared excess.
For environments that are not too dusty, the excess concentrates in molecular lines that trace the heated layer. Thus an accretionally heated atmosphere may be distinguished by its muted absorption bands. Irradiation from the accretion shock also changes the chemical composition of the atmosphere, further altering spectra.
Atmospheric retrievals promise to map out the deposition of accretional energy, helping to decide between ”hot” and ”cold” start modes of planet formation.
Nick Choksi, Peter Gao, Jerry Xuan, William Balmer, James Mang
Comments: To be submitted to ApJ. Comments welcome
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2610.12562 [astro-ph.EP] (or arXiv:2610.12562v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2610.12562
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Submission history
From: Nick Choksi
[v1] Thu, 8 Oct 2026 18:00:03 UTC (589 KB)
https://arxiv.org/abs/2610.12562
Astrobiology,
