Satellite formation around the largest asteroids

TL;DR

This paper demonstrates through simulations that impacts on rapidly rotating, elongated, porous asteroids can generate debris that forms stable satellites, explaining their observed distribution around large asteroids.

Contribution

It introduces a new impact-based formation pathway for satellites around large, elongated, porous asteroids, linking shape, rotation, and satellite formation.

Findings

Impacts on elongated, fast-rotating asteroids can produce debris that forms satellites.

Satellite formation is linked to the asteroid's shape and rotation, not just impact energy.

No correlation found between satellite presence and asteroid family membership.

Abstract

Satellites around large asteroids are preferentially found among those with the most rapid rotation and elongated shape. The taxonomic statistics are similarly skewed; in total, 13 asteroids larger than 100 km are known to have satellites, but none have been discovered among S-type asteroids. Previous modeling suggests that satellites could be generated by impacts, but spin and shape have never been tracked in models to relate collisional circumstances with those two observed properties concerning the primary. Here we show, by combining simulations of impacts into porous low-density asteroids, their subsequent disruption, reaccumulation and long-term satellite stability, a direct pathway for the formation of satellites. The immediate distortion and elongation of a rotating target body provides a launching point for some debris distinct from simple ballistic ejecta trajectories. The debris that are found to originate from the distorted long-axis is sourced primarily from 10-20 km below the surface and can be placed directly onto eccentric orbits with sufficiently large pericenter distances that avoid rapid re-impact. The specific energy and resultant total mass loss in satellite-forming collisions are not constraining, which explains the observed lack of correlation between asteroids with satellites and those that are part of large asteroid families.