Shape Modeling and Boulder Mapping of Asteroid 1992 UY4

The structure and history of near-Earth asteroids are important tostudy because they collide with Earth, sometimes with significant consequences forclimate and the survival of many species, including our own. If NASA is ever to deflect an asteroid on a collision course, it is crucial to know as much as possible about its size, composition, structure and boulder distribution. The boulderdistribution in turn helps to map the asteroid\u27s gravitational field.1992 UY4 is a near-Earth asteroid discovered in 1992. In August 2005, UY4 made a``close (for space) pass of Earth, about 15x farther than the Moon. It is the only chance to study the asteroid until its next pass near Earth in several hundred years. It was observed using the Arecibo Radio Observatory and a NASA tracking telescope in Goldstone, California. We used specialized software for radar analysis of asteroids, SHAPE, to study the asteroid\u27s detailed form, boulder distribution and pole orientation. We would like to determine whether boulders are uniformly distributed across UY4\u27s surface or not.To do this, SHAPE takes a series of parameters and generates syntheticdelay- Doppler radar images and compares them with the data from the observations.After producing models of 1992 UY4\u27s overall shape for each candidate pole direction, we mapped boulders/blocks in the radar images. In a preliminary analysis, mostof the boulder candidates have ambiguous locations on UY4\u27s surface -- they may beeither north or south of the asteroid\u27s equator. However, their locations in longitudeare unambiguous. So far, there is no indication of an inhomogeneous distribution of boulders in longitude. We continue to refine the models to explore the asteroid\u27scharacteristics in further detail