(100085) 1992 UY4

Radar Images of near-Earth Asteroid (100085) 1992 UY4

L. A. M. Benner, M. W. Busch, S. J. Ostro, J. D. Giorgini,
A. A. Hine, J. K. Harmon, M. C. Nolan, R. Rose, R. F. Jurgens, 
J. S. Jao, C. Magri, and J. L. Margot


We report Goldstone (8560-MHz, 3.5-cm) and Arecibo (2380-MHz, 13-cm) delay-Doppler radar images of 1992 UY4 that were obtained during August 1-10, 2005. The images achieve resolutions as fine as 7.5 m/pixel, place thousands of pixels on the object, and reveal a lumpy, modestly asymmetric, 2-km-diameter object whose shape resembles a meatball. The surface is characterized by gently undulating topography with many modest concavities. Numerous fine-scale, radar-bright features are evident at the trailing edges and limbs; one of the most prominent has a visible extent of about 100 m and juts out abruptly from the approaching limb, suggesting a large block similar to those seen on 25143 Itokawa by the Hayabusa spacecraft. The progression of features in the images is consistent with the photometrically-derived rotation period of 12.91 h and asymmetric lightcurve shape obtained by Warner et al. (2006, Minor Planet Bulletin 33, 20-21). If we assume that the diameter is twice the visible range extent, which would be true for a sphere, then the absolute magnitude of 17.6 and the 2-km-diameter correspond to an optical albedo of only ~0.04, strongly suggesting that 1992 UY4 is an optically-dark object. The radar data cover more than one-half of a rotation and the combined radar + photometric datasets should yield a detailed 3-D shape estimate.

An animation that shows 1992 UY4 rotating is available as a mov file.
Last updated: 2011 October 10