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.