Rotational effect as the possible cause of the east-west asymmetric crater rims on Ryugu observed by LIDAR data

TL;DR

This study suggests that the east-west asymmetry of crater rims on Ryugu may be caused by the asteroid's rotation, specifically when its surface speed approaches the first cosmic velocity, influencing ejecta trajectories.

Contribution

The paper provides a theoretical assessment linking asteroid rotation to crater rim asymmetry, proposing a specific rotation period (~3.6 h) as a key factor.

Findings

East-west asymmetry may result from rotation effects on ejecta trajectories.

Rotation speed near the first cosmic velocity influences crater rim morphology.

Observed crater features could indicate Ryugu's past rotation period.

Abstract

Asteroid 162173 Ryugu is a rubble-pile asteroid, whose top-shape is compatible with models of deformation by spin up. Rims of major craters on Ryugu have an east-west asymmetric profile; their western crater rims are sharp and tall, while their eastern crater rims are rounded and low. Although there are various possible explanations, we theoretically assess the effect of asteroid rotation as the possible reason for this east-west asymmetry. It is known that the trajectories and fates of ejecta are affected by the rotation. The Coriolis force and the inertial speed of the rotating surface are the factors altering the ejecta trajectories. Consequently, we found that the east-west asymmetric crater rims might be formed as a result of rotation, when the inertial speed of the rotating surface is nearly equal to the first cosmic velocity of the body. In other words, it is possible that the observed east-west asymmetric rims of the Urashima, Cendrillon, and Kolobok craters were formed when Ryugu's rotation period was ~3.6 h.