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IMAGE CAPTION                                        8/26/99

     Radar images of newly discovered 1999 JM8, an unusually 
large asteroid with a slow rotation rate, reveal the object's 
bizarre shape as it streaked past Earth in late July and early 
August at a close approach of 8.5 million kilometers (5.3 million 
miles), about 22 times the distance between the Earth and the 
Moon.  The object, thought to be several miles wide, was captured 
by a radar team led by Dr. Lance Benner of NASA's Jet Propulsion 
Laboratory, Pasadena, CA, after its discovery on May 13, 1999, 
using NASA's Goldstone radar facility in California and the 
Arecibo Observatory's radar in Puerto Rico.  

     The images, clockwise from the top left, were taken on 
August 5, July 28, August 2 and August 1. Radar illumination is 
from the top and the asteroid's rotation is clockwise. The 
Goldstone images taken on July 28 have a vertical resolution of 
38 meters per pixel and those taken on August 1 have a vertical 
resolution of 19 meters per pixel.  The images taken by the 
Arecibo Observatory on August 2 and 5 have a vertical resolution 
of 15 meters per pixel.
 
     1999 JM8 resembles Toutatis, a similarly sized, slowly 
rotating asteroid that also crosses Earth's orbit and that last 
flew past the planet on November 29, 1996, at a close approach of 
5.3 million kilometers (3.3 million miles). Discovery of a second 
large Earth-crosser with a similarly slow spin rate suggests that 
slowly tumbling asteroids are fairly common among near-Earth 
objects. However, although collisions are thought to be the 
primary process determining asteroid spin states, astronomers do 
not know how these slow, complex rotation states come about. 

     1999 JM8 was discovered with a U. S. Air Force telescope in 
New Mexico that is part of MIT's Lincoln Near Earth Asteroid 
Research project. Radar observations by Ostro, Benner and their 
team were supported by NASA's Office of Space Science, 
Washington, DC.  The Goldstone Solar System Radar is part of 
NASA's Deep Space Network.  The Arecibo Observatory, in Puerto 
Rico, is part of the National Astronomy and Ionosphere Center, 
which is operated by the Cornell University under a cooperative 
agreement with the National Science Foundation and with support 
from NASA.  JPL is a division of the California Institute of 
Technology, Pasadena, CA.

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