Estimation of Interior Density Distribution for Small Bodies: The Case of Asteroid Itokawa

Abstract

A constraint of rubble-pile interior is an essential issue for better understanding of its formation scenario such as catastrophic disruption and reconfiguration. A goal of this study is to demonstrate a method to constrain unknown density distribution within a small solar system body. We calculated the gravity field on the surface of asteroid 25143 Itokawa using a 3D shape model. We assumed density inhomogeneity between two lobes of Itokawa; “Head” and “Body” of the sea-otter-like shape. Then, we estimated interior density distribution of Itokawa as an index of the gravity potential variance (and surface slope average). This study implied that the Head of Itokawa had a more monolithic structure of significantly higher density than the remaining Body part. The density of the Head was evaluated as ～ 2,750 kg/m³, which is much higher than the Itokawa's mean density of 1,950 kg/m³. Such a dramatic density anomaly corresponds to a great offset between the center-of-mass (COM) and the center-of-figure (COF) by ~ 16 m. This result implies interior density inhomogeneity within a rubble-pile asteroid.