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

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 $\lambda =237.7^{\circ }$ and $\beta =-83.8^{\circ }$ considering the observation uncertainties, and its rotation period is $\sim$ 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 $p_{\mathrm{v}}=0.045\pm 0.002$, $D_{\mathrm{eff}}=1.69_{-0.02}^{+0.05}$ km. The diameters of the primary and secondary are determined to be $D_1=1.63_{-0.03}^{+0.04}$ km and $D_2=0.45_{-0.03}^{+0.04}$ km, respectively. The surface thermal inertia $\Gamma$ is derived to be a low value of $80\pm 40\mathrm{J}{\mathrm{m}}^{-2}{\mathrm{s}}^{-0.5}{\mathrm{K}}^{-1}$ with a roughness fraction $f_{\mathrm{R}}$ of $0.8_{-0.4}^{+0.2}$. 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 $5\sim 20\mathrm{mm}$ from the simulations of subsurface temperature distribution, indicating that 1996 FG3 could be a very suitable target for a sample return mission.

15 pages, 11 figures, 9 tables, accepted to MNRAS

References in corpus (2)

• Thermal inertia of near-Earth asteroids and implications for the magnitude of the Yarkovsky effect
• Physical characterization and origin of binary near-Earth asteroid (175706) 1996 FG3

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