"Isocrater" impacts: Conditions and mantle dynamical responses for different impactor types

TL;DR

This study derives conditions for impacts of different types to produce identical craters and explores how impactor type influences planetary interior anomalies, with implications for planetary history and impactor demographics.

Contribution

It introduces a theoretical framework for isocrater impacts and analyzes how impactor type affects interior anomalies across different planets.

Findings

Asteroidal impacts produce smaller interior anomalies than cometary impacts for the same crater size.

Interior anomalies from large impacts are preserved on Mars, Moon, and Mercury but are erased on Venus.

Impact signatures can help identify impactor types and constrain ancient impactor populations.

Abstract

Impactors of different types and sizes can produce a final crater of the same diameter on a planet under certain conditions. We derive the condition for such "isocrater impacts" from scaling laws, as well as relations that describe how the different impactors affect the interior of the target planet; these relations are also valid for impacts that are too small to affect the mantle. The analysis reveals that in a given isocrater impact, asteroidal impactors produce anomalies in the interior of smaller spatial extent than cometary or similar impactors. The differences in the interior could be useful for characterizing the projectile that formed a given crater on the basis of geophysical observations and potentially offer a possibility to help constrain the demographics of the ancient impactor population. A series of numerical models of basin-forming impacts on Mercury, Venus, the Moon, and Mars illustrates the dynamical effects of the different impactor types on different planets. It shows that the signature of large impacts may be preserved to the present in Mars, the Moon, and Mercury, where convection is less vigorous and much of the anomaly merges with the growing lid. On the other hand, their signature will long have been destroyed in Venus, whose vigorous convection and recurring lithospheric instabilities obliterate larger coherent anomalies.