Asteroid 1996 FG3 Characterized as a Potential Sample Return Target

Shape, Thermal and Surface Properties determination of a Candidate Spacecraft Target Asteroid (175706) 1996 FG3

Authors:

Yu et al

Abstract:

In this paper, a 3D convex shape model of (175706) 1996 FG3, which consists of 2040 triangle facets and 1022 vertices, is derived from the known lightcurves. The best-fit orientation of the asteroid's spin axis is determined to be λ=237.7∘ and β=−83.8∘ considering the observation uncertainties, and its rotation period is ∼ 3.5935 h . Using the derived shape model, we adopt the so-called advanced thermophysical model (ATPM) to fit three published sets of mid-infrared observations of 1996 FG3 \citep{Wolters2011,Walsh2012}, so as to evaluate its surface properties. Assuming the primary and the secondary bear identical shape, albedo, thermal inertia and surface roughness, the best-fit parameters are obtained from the observations. The geometric albedo and effective diameter of the asteroid are reckoned to be pv=0.045±0.002, Deff=1.69+0.05−0.02 km. The diameters of the primary and secondary are determined to be D1=1.63+0.04−0.03 km and D2=0.45+0.04−0.03 km, respectively. The surface thermal inertia Γ is derived to be a low value of 80±40Jm−2s−0.5K−1 with a roughness fraction fR of 0.8+0.2−0.4. This indicates that the primary possibly has a regolith layer on its surface, which is likely to be covered by a mixture of dust, fragmentary rocky debris and sand. The minimum regolith depth is estimated to be 5∼20mm from the simulations of subsurface temperature distribution, indicating that 1996 FG3 could be a very suitable target for a sample return mission.