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Schedule including this lecture.
Goddard Space Flight Center Engineering Colloquium
Date: Monday, December 4, 2000
The NEAR Shoemaker spacecraft entered orbit around the near Earth asteroid 433 Eros on February 14, 2000. Since then, intensive observations from orbit have revealed that Eros is a complex and fascinating object. NEAR Shoemaker has measured the first x-rays and obtained the first laser altimetric data from an asteroid. Eros has a highly irregular shape, with a maximum linear dimension of 32.7 km but a minimum diameter of 7 km from the bottom of the 5 km crater to the bottom of the saddle-shaped depression on the opposite side of the asteroid. The average density of Eros is about that of Earth's crust, and it is almost uniform, but there are suggestions of a small density variation. The bulk elemental composition of Eros indicates that Eros is not a differentiated body, so it never underwent melting and separation into distinct compositional layers as did the Earth and the other terrestrial planets. A primitive, undifferentiated composition is also inferred from visible and near infrared spectra. We are still searching for evidence of partial melting and small scale compositional heterogeneity. The composition of Eros may be consistent with that of the important class of primitive meteorites known as ordinary chondrites. We are also searching for intrinsic magnetization of Eros. The surface of Eros is surprising in many ways. There is a pervasive global fabric consisting of a variety of ridges, grooves, and chains of pits or craters. Many craters have shapes that imply significant strength in the surface material of Eros. Some regions appear to be extensively resurfaced. Several landslides have been identified on Eros. Some topographic features, including a ridge system several kilometers long and over 100 m high in places, indicate tectonic deformations. Contrary to theoretical predictions, Eros does not appear to be a loosely bound collection of much smaller component bodies. Some global scale linear features suggest that Eros may once have been part of a much larger body
Dr. Andrew F. Cheng is a Principal Professional Staff member at the Johns Hopkins University Applied Physics Laboratory, where he is currently supervisor of the Theoretical Space Physics section. He obtained an AB in physics from Princeton University in 1971 and a Ph. D. in physics from Columbia University in 1977. His scientific interests include surface processes on small bodies, space plasma and astrophysical fluid dynamics, interactions of plasmas with atmospheres and solid surfaces, and magnetospheric physics. He is the Project Scientist for the Near-Earth Asteroid Rendezvous mission of the NASA Discovery Program. He is the Orbital LIDAR scientist on the ISAS-NASA MUSES-C mission to a near-Earth asteroid and a co-investigator on the CASSINI mission to Saturn. He was an Interdisciplinary Scientist on the GALILEO mission to Jupiter. He is a fellow of the American Physical Society and a former editor of EOS-Transactions of the American Geophysical Union. He has served as an associate editor for the Journal of Geophysical Research and for Geophysical Research Letters. He has served on several NASA and National Academy of Science advisory committees.
Colloquium Committee Sponsor: Dave Beyer
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