UCLA

Three-body model fits to Arecibo and Goldstone radar data reveal the nature of two near-Earth asteroid triples. The triple-asteroid system 2001 SN263 is characterized by a primary of ∼1013 kg, an inner satellite 1% as massive orbiting at c∼3 primary radii in 0.7 days, and an outer satellite ∼2.5% as massive orbiting at ∼13 primary radii in 6.2 days. 1994 CC is a smaller system with a primary of mass ∼2.6 ×1011 kg and two satellites 2% and ≲1% as massive orbiting at distances of ∼5.5 and ∼19.5 primary radii. Their orbital periods are 1.2 and 8.4days. Examination of resonant arguments shows that the satellites are not currently in a mean-motion resonance. Precession of the apses and nodes are detected in both systems (2001 SN263 inner body: d/dt 1.1 deg day-1; 1994 CC inner body: d/dt ∼ -0.2 deg day-1), which is in agreement with analytical predictions of the secular evolution due to mutually interacting orbits and primary oblateness. Nonzero mutual inclinations between the orbital planes of the satellites provide the best fits to the data in both systems (2001 SN263: 14deg; 1994 CC: 16 ∼ deg). Our best-fit orbits are consistent with nearly circular motion, except for 1994 CC's outer satellite which has an eccentric orbit of e ∼ 0.19. We examine several processes that can generate the observed eccentricity and inclinations, including the Kozai and evection resonances, past mean-motion resonance crossings, and close encounters with terrestrial planets. In particular, we find that close planetary encounters can easily excite the eccentricities and mutual inclinations of the satellites' orbits to the currently observed values. © 2011. The American Astronomical Society. All rights reserved.