Fracture analysis on asteroid Ryugu

Abstract

Fractures in boulders on the Near-Earth-Asteroid Ryugu were mapped and analysed in this work, using image data from the Japanese Hayabusa-2 mission. This resulted in orientation distributions and length distribution of the fractures. The preferred orientation of the fractures is North-South, relative to Ryugu’s equator. The likely explanation for this distribution is the thermal influence under which these fractures formed: The sun illuminates the east side of the boulders in the morning and the west side in the evening, resulting in a thermal gradient in the east-west direction, the thermal gradient in a stress distribution that promotes crackgrowth in the north-south direction. The distribution of fracture lengths determined for Ryugu is similar to the fractures on another asteroid, Bennu, which also orbits in a near-Earth orbit. The length distribution can be explained by describing the thermal influence with an exponential law and the size of the boulders (and thus also the fractures) with a power law. The length distribution was also used to model the temporal sequence of fracture growth to obtain time scales when fracture growth occurred and the observed length distributions could have formed.