THE ORIGIN OF ASTEROID 101955 (1999 RQ36)

Abstract

Near-Earth asteroid (NEA) 101955 (1999 RQ₃₆; henceforth RQ36) is especially accessible to spacecraft and is the primary target of NASA's OSIRIS-REx sample return mission; it is also a potentially hazardous asteroid. We combine dynamical and spectral information to identify the most likely main-belt origin of RQ36 and we conclude that it is the Polana family, located at a semimajor axis of about 2.42 AU. We also conclude that the Polana family may be the most important inner-belt source of low-albedo NEAs. These conclusions are based on the following results. (1) Dynamical evidence strongly favors an inner-belt, low-inclination (2.15 AU < a < 2.5 AU and i < 10°) origin, suggesting the ν₆ resonance as the preferred (95% probability) delivery route. (2) This region is dominated by the Nysa and Polana families. (3) The Polana family is characterized by low albedos and B-class spectra or colors, the same albedo and spectral class as RQ36. (4) The Sloan Digital Sky Survey colors show that the Polana family is the branch of the Nysa-Polana complex that extends toward the ν₆ resonance; furthermore, the Polana family has delivered objects of the size of RQ36 and larger into the ν₆ resonance. (5) A quantitative comparison of visible and near-infrared spectra does not yield a unique match for RQ36; however, it is consistent with a compositional link between RQ36 and the Polana family.