Physical Characterization and Origin of Binary Near-Earth Asteroid (175706) 1996 FG3

The near-Earth asteroid (NEA) (175706) 1996 FG3 is a particularly interesting spacecraft target: a binary asteroid with a low-Δv heliocentric orbit. The orbit of its satellite has provided valuable information about its mass density while its albedo and colors suggest it is primitive or part of the C-complex taxonomic grouping. We extend the physical characterization of this object with new observations of its emission at mid-infrared wavelengths and with near-infrared reflection spectroscopy. We derive an area-equivalent system diameter of 1.90 ± 0.28 km (corresponding to approximate component diameters of 1.83 km and 0.51 km, respectively) and a geometric albedo of 0.039 ± 0.012. (175706) 1996 FG3 was previously classified as a C-type asteroid, though the combined 0.4-2.5 μm spectrum with thermal correction indicates classification as B-type; both are consistent with the low measured albedo. Dynamical studies show that (175706) 1996 FG3 most probably originated in the inner main asteroid belt. Recent work has suggested the inner Main Belt (142) Polana family as the possible origin of another low-Δv B-type NEA, (101955) 1999 RQ36. A similar origin for (175706) 1996 FG3 would require delivery by the overlapping Jupiter 7:2 and Mars 5:9 mean motion resonances rather than the ν6, and we find this to be a low probability, but possible, origin. Partially based on observations obtained at the European Southern Observatory (ESO, program ID 383.C-0179A). Observations were also obtained at the Infrared Telescope Facility, which is operated by the University of Hawaii under Cooperative Agreement No. NCC 5-538 with the National Aeronautics and Space Administration, Science Mission Directorate, Planetary Astronomy Program