![Atmospheric evolution with and without a post-disk giant impact. Panel 1: The common initial state for a rocky planet with a hydrogen-rich atmosphere. Panels 2a–4a: A giant impact deposits energy into the mantle and core, but the increase in gravitational binding energy dominates, allowing the planet to retain its hydrogen-rich atmosphere and evolve into a sub-Neptune (1.75−3.5 R⊕). Panels 2b–4b: In the absence of such an impact, the planet is less massive, loses its primordial atmosphere under sustained stellar irradiation, and becomes a super-Earth (1−1.75 R⊕). -- [astro-ph.EP]](https://i0.wp.com/astrobiology.com/wp-content/uploads/2026/10/Retention.png?fit=1200%2C681&ssl=1)
[astro-ph.EP] Rocky planets the size of Earth or larger are expected to undergo one or more giant impacts during the final stages of their formation.
Some of these collisions occur after protoplanetary disk dissipation, potentially driving the loss of primordial hydrogen-rich atmospheres through elevated surface temperatures. However, whether giant impacts promote atmospheric loss or retention remains unclear because they both heat planetary interiors and increase atmospheric gravitational binding.
Here we model the evolution of rocky planets after their largest post-disk giant impact, accounting self-consistently for the concurrent increase in gravitational binding energy and mantle thermal energy. Whereas the entire accreted mass contributes to the increase in gravitational binding energy, only part of the impact energy raises mantle temperature.
Mantle melting consumes energy as latent heat, while the impactor’s metallic core transfers little energy to the mantle and remains superheated at depth. Giant impacts therefore increase gravitational binding energy more than mantle thermal energy, shifting planets towards atmospheric retention. Larger, atmosphere-bearing planets emerge preferentially through collisional growth.
By contrast, smaller planets without such impacts tend to lose their primordial atmospheres under sustained stellar irradiation. At the population level, these results suggest that sub-Neptunes have, on average, more massive rocky interiors than super-Earths.
Darius Modirrousta-Galian, Jun Korenaga
Comments: 34 pages, 6 main figures and 2 extended figures. Published in Nature Astronomy
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2610.36446 [astro-ph.EP] (or arXiv:2610.36446v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2610.36446
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Related DOI:
https://doi.org/10.1038/s41550-026-03006-1
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Submission history
From: Darius Modirrousta-Galian
[v1] Tue, 27 Oct 2026 00:49:40 UTC (9,069 KB)
https://arxiv.org/abs/2610.36446
Astrobiology,
