September 28, 2007
This is the story of the two asteroids which have not only been visited by spacecraft, but which have hosted asteroid landings. They are Eros and Itokawa, which were visited by NEAR and Hayabusa, respectively. I have had the good fortune to work on both missions. NEAR was the first APL planetary mission and the first NASA planetary mission not implemented at a NASA center. I will talk about the ways in which NEAR has changed our thinking about asteroids and will present an update of science results. I will present science results from Hayabusa at Itokawa and discuss why we think Itokawa is the first object confirmed to be a rubble pile. In some sense, the history of asteroids is a history of catastrophic disruption. By that I do not mean the destruction that would happen if either asteroid ever hits the Earth -- although both Eros and Itokawa are in orbits that may, millions of years from now, do just that -- but what happens when asteroids collide with each other. Both asteroids have surfaces that show evidence of recent geologic activity.
Dr. Andrew F. Cheng is a principal staff physicist in the Space Department of the Johns Hopkins University Applied Physics Laboratory. He received a Ph.D. degree in physics from Columbia University in 1977. He was a post-doctoral fellow at AT&T Bell Laboratories and an assistant professor of physics at Rutgers University prior to joining the Applied Physics Laboratory in 1983. He has been an Interdisciplinary Scientist on the Galileo mission to Jupiter, a Co-Investigator on the Cassini mission to Saturn, and a team member on the MUSES-C mission to a near-Earth asteroid. He has been the Project Scientist for the Near Earth Asteroid Rendezvous (NEAR) mission to asteroid Eros. He is currently a science team member on the Mercury Surface, Space Environment, Geochemistry, and Ranging (MESSENGER) mission and the New Horizons mission to Pluto and the Kuiper Belt. Dr. Cheng is a fellow of the American Physical Society and a member of the American Geophysical Union and the American Astronomical Society. He is currently on detail to NASA Headquarters, serving as Deputy Chief Scientist for Space Sciences.