Graze-and-Merge Collisions under External Perturbers

TL;DR

This paper investigates how external gravitational perturbers influence graze-and-merge collisions between planetary bodies, revealing that larger loop-back orbits lead to more chaotic outcomes and potential escape of the smaller body.

Contribution

It provides a detailed analysis of how external perturbers affect the dynamics and outcomes of graze-and-merge collisions in planetary systems.

Findings

Loop-back orbits within 1/3 Hill radius are minimally affected by external perturbers.

Larger loop-back orbits increase randomness in collision parameters.

Orbits around 3/4 Hill radius often lead to the smaller body's escape.

Abstract

Graze-and-merge collisions (GMCs) are common multi-step mergers occurring in low-velocity off-axis impacts between similar sized planetary bodies. The first impact happens at somewhat faster than the mutual escape velocity; for typical impact angles this does not result in immediate accretion, but the smaller body is slowed down so that it loops back around and collides again, ultimately accreting. The scenario changes in the presence of a third major body, i.e. planets accreting around a star, or satellites around a planet. We find that when the loop-back orbit remains inside roughly 1/3 of the Hill radius from the target, then the overall process is not strongly affected. As the loop-back orbit increases in radius, the return velocity and angle of the second collision become increasingly random, with no record of the first collision's orientation. When the loop-back orbit gets to about 3/4 of the Hill radius, the path of smaller body is disturbed up to the point that it will usually escape the target.