Giant impacts punish thinner atmospheres hardest

Matthew Roche and colleagues used smoothed-particle hydrodynamics to simulate giant impacts on worlds whose atmospheres contain one to twenty percent of planetary mass. They find that lower-mass, lower-pressure atmospheres are substantially easier to strip than existing simplified prescriptions often assume, and derive a scaling relation intended for planet-formation models from embryos through super-Earths and sub-Neptunes.

When applied to Solar System formation simulations, the revised relation produces frequent major loss events for bodies smaller than about 0.6 Earth masses. Repeated impacts can remove 30 to 100 percent of the atmospheres of roughly Earth-mass bodies in the modeled histories, while the Moon-forming impact's effect varies sharply with starting atmosphere and collision geometry. These are simulations and scaling laws, not direct reconstructions of any single planet's past.

Why it matters

Atmospheric survival shapes surface conditions and habitability. A model that accounts for how much gas a world starts with can change which young planets are expected to retain—or repeatedly rebuild—their envelopes.

What the source establishes

Fresh preprint submitted October 5. The scaling law is derived from three-dimensional simulations and tested in formation models; empirical application to specific exoplanets will require observational constraints.