Binary craters on Ceres and Vesta and implications for binary asteroids

TL;DR

This study identifies and analyzes binary craters on Ceres and Vesta to infer properties of their impactors, revealing evidence of well-separated, similarly sized binary asteroids with nonzero obliquity, differing from current impact models.

Contribution

The paper provides the first identification of binary craters on Ceres and Vesta and compares their orientations with impact simulations, suggesting a population of binary asteroids with nonzero obliquity.

Findings

39 binary craters on Ceres

18 binary craters on Vesta

Binary impactors are widely separated and similar in size

Abstract

Context. Airless planetary objects have their surfaces covered by craters, and these can be used to study the characteristics of asteroid populations. Planetary surfaces present binary craters that are associated with the synchronous impact of binary asteroids. Aims. We identify binary craters on asteroids (1) Ceres and (4) Vesta, and aim to characterize the properties (size ratio and orbital plane) of the binary asteroids that might have formed them. Methods. We used global crater databases developed in previous studies and mosaics of images from the NASA DAWN mission high-altitude and low-altitude mapping orbits. We established selection criteria to identify craters that were most likely a product of the impact of a binary asteroid. We performed numerical simulations to predict the orientation of the binary craters assuming the population of impactors has mutual orbits coplanar with heliocentric orbits, as the current census of binary asteroids suggests. We compared our simulations with our survey of binary craters on Ceres and Vesta through a Kolmogorov-Smirnov test. Results. We find geomorphological evidence of 39 and 18 synchronous impacts on the surfaces of Ceres and Vesta, respectively. The associated binary asteroids are widely separated and similar in diameter. The distributions of the orientation of these binary craters on both bodies are statistically different from numerical impact simulations that assume binary asteroids with coplanar mutual and heliocentric orbits. Conclusions. Although the identification of binary craters on both bodies and the sample size are limited, these findings are consistent with a population of well-separated and similarly sized binary asteroids with nonzero obliquity that remains to be observed, in agreement with the population of binary craters identified on Mars.