Dark Primitive Asteroids Account for a Large Share of K/Pg-Scale Impacts on the Earth

TL;DR

This study models large near-Earth asteroids to estimate impact rates and origins, revealing dark primitive asteroids' significant role in K/Pg-scale impacts and suggesting a main belt origin for the impactor that caused the mass extinction 66 million years ago.

Contribution

It provides a dynamical model quantifying impact rates of large NEAs and their composition, highlighting the importance of dark primitive asteroids in Earth's impact history.

Findings

16-32 impacts of D>5 km NEAs expected in 1 Gyr

About half of impactors are dark primitive asteroids

The K/Pg impactor likely originated beyond 2.5 au

Abstract

A dynamical model for large near-Earth asteroids (NEAs) is developed here to understand the occurrence rate and nature of Cretaceous-Paleogene (K/Pg) scale impacts on the Earth. We find that 16--32 (2--4) impacts of diameter $D>5$ km ($D>10$ km) NEAs are expected on the Earth in 1 Gyr, with about a half of impactors being dark primitive asteroids (most of which start with semimajor axis $a>2.5$ au). These results explain why the Chicxulub crater, the third largest impact structure found on the Earth (diameter $\simeq180$ km), was produced by impact of a carbonaceous chondrite. They suggest, when combined with previously published results for small ($D \lesssim 1$ km) NEAs, a size-dependent sampling of the main belt. We conclude that the impactor that triggered the K/Pg mass extinction $\simeq 66$ Myr ago was a main belt asteroid that quite likely ($\simeq 60$\% probability) originated beyond 2.5 au.