Internal rubble properties of asteroid (101955) Bennu

TL;DR

This study uses gravity data and statistical modeling to analyze the internal structure of asteroid Bennu, revealing heterogeneities, a lower density core, and details about the size distribution of its internal rubble.

Contribution

It introduces a combined gravity inversion and rubble-pile model approach to characterize Bennu's interior properties and rubble size distribution.

Findings

Rubble-pile density is about 1.35 g/cm³ with 12% porosity.

Interior rubble size distribution index is approximately -2.9.

Largest internal rubble particle is about 145 meters.

Abstract

Exploration of asteroid (101955) Bennu by the OSIRIS-REx mission has provided an in-depth look at this rubble-pile near-Earth asteroid. In particular, the measured gravity field and the detailed shape model of Bennu indicate significant heterogeneities in its interior structure, compatible with a lower density at its center. Here we combine gravity inversion methods with a statistical rubble-pile model to determine the density and size-frequency distribution (SFD) index of the rubble that constitutes Bennu. The best-fitting models indicate that the SFD of the interior is consistent with that observed on the surface, with a cumulative SFD index of approximately $-2.9$. The rubble bulk density is approximately $1.35$ g/cm$^3$, corresponding to a $12$% macro-porosity. We find the largest rubble particle to be approximately $145$ m, whereas the largest void is approximately $10$ m.