Radar and optical observations and physical modeling of near-Earth Asteroid 10115 (1992 SK)

We estimate Asteroid 1992 SK's physical properties from delay–Doppler images and Doppler-only echo spectra obtained during March 22–27, 1999, at Goldstone and from optical lightcurves obtained during February–March 1999 at Ondřejov Observatory. The images span only about 15° of sky motion and are not strong, but they place up to twenty 40 m by 160 m pixels on the asteroid and have complete rotational phase coverage. Our analysis establishes that the radar observations are confined to subradar latitudes between −20° and −40°. The echo spectra and optical lightcurves span ∼80° of sky motion, which provides important geometric leverage on the pole direction. The lightcurves are essential for accurate estimation of the asteroid's shape and spin state. We estimate the asteroid's period to be 7.3182±0.0003 h7.3182±0.0003 h and its pole direction to be at ecliptic longitude, latitude=(99°±5°,−3°±5°)=(99°±5°,−3°±5°). The asteroid is about 1.4 km in maximum extent and mildly asymmetric, with an elongation of about 1.5 and relatively subdued topography. The OC radar albedo is 0.11±0.020.11±0.02 and the SC/OC ratio is 0.34±0.050.34±0.05. The current orbital solution permits accurate identification of planetary close approaches during 826–2690. We use our model to predict salient characteristics of radar images and optical lightcurves obtainable during the asteroid's March 2006 approach.