Thermophysical Characteristics of OSIRIS-REx Target Asteroid (101955) Bennu

TL;DR

This study determines the thermophysical properties of asteroid Bennu, revealing surface characteristics like grain size and thermal inertia, which are crucial for the OSIRIS-REx sample return mission.

Contribution

It provides updated thermophysical parameters of Bennu using a 3D shape model and infrared data, aiding mission planning and understanding of asteroid surface properties.

Findings

Bennu's diameter is approximately 510 meters.

Thermal inertia suggests fine-grained surface material.

Surface grain size varies from 1.3 to 31 mm.

Abstract

In this work, we investigate the thermophysical properties, including thermal inertia, roughness fraction and surface grain size of OSIRIS-REx target asteroid (101955) Bennu by using a thermophysical model with the recently updated 3D radar-derived shape model (\cite[Nolan et al., 2013]{Nolan2013}) and mid-infrared observations (\cite[M$\ddot{u}$ller et al, 2012]{Muller2012}, \cite[Emery et al., 2014]{Emery2014}). We find that the asteroid bears an effective diameter of $510^{+6}_{-40}$ m, a geometric albedo of $0.047^{+0.0083}_{-0.0011}$, a roughness fraction of $0.04^{+0.26}_{-0.04}$, and thermal inertia of $240^{+440}_{-60}\rm~Jm^{-2}s^{-0.5}K^{-1}$ for our best-fit solution. The best-estimate thermal inertia suggests that fine-grained regolith may cover a large portion of Bennu's surface, where a grain size may vary from $1.3$ to $31$~mm. Our outcome suggests that Bennu is suitable for the OSIRIS-REx mission to return samples to Earth.