Atmospheric Erosion by Giant Impacts onto Terrestrial Planets

Abstract

We examine the mechanisms by which atmosphere can be eroded by giant impacts onto Earth-like planets with thin atmospheres, using 3D smoothed particle hydrodynamics simulations with sufficient resolution to directly model the fate of low-mass atmospheres. We present a simple scaling law to estimate the fraction lost for any impact angle and speed in this regime. In the canonical Moon-forming impact, only around 10% of the atmosphere would have been lost from the immediate effects of the collision. There is a gradual transition from removing almost none to almost all of the atmosphere for a grazing impact as it becomes more head-on or increases in speed, including complex, non-monotonic behaviour at low impact angles. In contrast, for head-on impacts, a slightly greater speed can suddenly remove much more atmosphere. Our results broadly agree with the application of 1D models of local atmosphere loss to the ground speeds measured directly from our simulations. However, previous analytical models of shock-wave propagation from an idealised point-mass impact significantly underestimate the ground speeds and hence the total erosion. The strong dependence on impact angle and the interplay of multiple non-linear and asymmetrical loss mechanisms highlight the need for 3D simulations in order to make realistic predictions.

19 pages, 13 figures, published in ApJ

References in corpus (5)

• Atmospheric Mass Loss During Planet Formation: The Importance of Planetesimal Impacts
• Evidence for multiple magma ocean outgassing and atmospheric loss episodes from mantle noble gases
• A giant impact as the likely origin of different twins in the Kepler-107 exoplanet system
• Inefficient volatile loss from the Moon-forming disk: reconciling the giant impact hypothesis and a wet Moon
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• Impact Induced Atmosphere-Mantle Exchange Sets the Volatile Elemental Ratios on Primitive Earths
• The effect of pre-impact spin on the Moon-forming collision
• Unified simulations of planetary formation and atmospheric evolution II: Rapid disk clearing by photoevaporation yields low-mass super-Earth atmospheres
• Size evolution of close-in super-Earths through giant impacts and photoevaporation
• Origin of Mars's moons by disruptive partial capture of an asteroid
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• Exploring the catastrophic regime: thermodynamics and disintegration in head-on planetary collisions
• Takeout and Delivery: Erasing the Dusty Signature of Late-stage Terrestrial Planet Formation
• Evolution and Observable Properties of Rocky Planet Atmospheres
• Re-accretion of Giant Impact Ejecta Can Drive Significant Atmospheric Erosion on Terrestrial Planets
• Refining the Masses and Radii of the Star Kepler-33 and its Five Transiting Planets