# Giant impacts shift rocky planets toward keeping primordial atmospheres, model shows

- Published: 2026-11-05 20:03 UTC
- Section: Sky & Space › Astronomy
- Tags: giant impacts, atmospheric retention, primordial hydrogen atmosphere, gravitational binding energy, mantle melting, sub-Neptunes, super-Earths, planet formation model, Korenaga, Modirrousta-Galian
- URL: https://realtech.media/news/rt-aeb28ecddf7958f47a19c34f_giant_impacts_shift/

**A Nature Astronomy model finds that giant impacts raise atmospheric gravitational binding more than mantle thermal energy, so larger planets tend to keep hydrogen-rich envelopes.**

![Giant impacts shift rocky planets toward keeping primordial atmospheres, model shows](https://sgzwpqqelzmajkcubgkl.supabase.co/storage/v1/object/public/rt-media/2026/11/60acc8be2d2e54a9.png)
*nature.com*

Darius Modirrousta-Galian (Shanghai Jiao Tong University) and Jun Korenaga (Yale) modelled how rocky planets evolve after their largest giant impact following the dissipation of the protoplanetary disk. The work, titled "Retention of primordial atmospheres through giant impacts" and published in Nature Astronomy (nature.com), concludes that such impacts shift planets toward retaining primordial hydrogen-rich atmospheres rather than losing them [1].

## Two effects of one collision

Rocky planets the size of Earth or larger are expected to undergo one or more giant impacts in the final stages of formation. Some of these collisions happen after the disk has dissipated and could, in principle, drive atmospheric loss by raising surface temperatures [1]. Yet an impact also heats the planetary interior and increases the gravitational binding of the atmosphere, so the net outcome had remained unclear [1].

The authors account for both changes self-consistently. The entire accreted mass contributes to the increase in gravitational binding energy, whereas only part of the impact energy raises the temperature of the mantle [1]. Mantle melting consumes energy as latent heat, and the impactor's metallic core transfers little energy to the mantle and stays superheated at depth [1]. As a result, giant impacts increase gravitational binding energy more than mantle thermal energy [1].

"Their effect on a planet's atmosphere depends on how those two changes work together," Korenaga said.

## Consequences for planet populations

According to the model, larger planets that carry atmospheres emerge preferentially through collisional growth [1]. Smaller planets that avoid such impacts tend to lose their primordial atmospheres under sustained stellar irradiation [1].

At the population level, the authors suggest that sub-Neptunes have, on average, more massive rocky interiors than super-Earths [1]. The study is theoretical: the synthetic data were generated with code the authors published on Zenodo, and the observational data in the paper's figures come from an earlier survey of the small-planet radius distribution [1].

## Sources

1. [nature.com](https://www.nature.com/articles/s41550-026-03006-1)
2. [universetoday.com](https://www.universetoday.com/articles/giant-impacts-help-rocky-planets-retain-their-atmospheres)

---

Source: RealTech, realtech.media — https://realtech.media/news/rt-aeb28ecddf7958f47a19c34f_giant_impacts_shift/