Physical modeling of triple near-Earth Asteroid (153591) 2001 SN263 from radar and optical light curve observations

Abstract

We report radar observations (2380-MHz, 13-cm) by the Arecibo Observatory and optical light curves observed from eight different observatories and collected at the Ondřejov Observatory of the triple near-Earth asteroid system (153591) 2001 SN263. The radar observations were obtained over the course of ten nights spanning February 12–26, 2008 and the light curve observations were made throughout January 12 - March 31, 2008. Both data sets include observations during the object’s close approach of 0.06558 AU on February 20th, 2008. The delay-Doppler images revealed the asteroid to be comprised of three components, making it the first known triple near-Earth asteroid. Only one other object, (136617) 1994 CC is a confirmed triple near-Earth asteroid. We present physical models of the three components of the asteroid system. We constrain the primary’s pole direction to an ecliptic longitude and latitude of (309°,-80°)±15°. We find that the primary rotates with a period 3.4256±0.0002h and that the larger satellite has a rotation period of 13.43±0.01h, considerably shorter than its orbital period of approximately 6 days. We find that the rotation period of the smaller satellite is consistent with a tidally locked state and therefore rotates with a period of 0.686±0.002 days (Fang et al. [2011]. Astron. J. 141, 154–168). The primary, the larger satellite, and the smaller satellite have equivalent diameters of 2.5±0.3km, 0.77±0.12km, 0.43±0.14km and densities of 1.1±0.2g/cm3,1.0±0.4g/cm3,2.3±1.3g/cm3, respectively.