Donald Savage
Headquarters, Washington, DC                      May 4, 2000
(Phone: 202/358-1547) 

Jane Platt
Jet Propulsion Laboratory, Pasadena, CA
(Phone: 818/354-0880)

RELEASE:  00-74

ASTRONOMERS CATCH IMAGES OF GIANT METAL DOG BONE ASTEROID

     NASA astronomers have collected the first-ever radar images 
of a "main belt" asteroid, a metallic, dog bone-shaped rock the 
size of New Jersey, an apparent leftover from an ancient, violent 
cosmic collision.

     The asteroid, named 216 Kleopatra, is a large object in the 
main asteroid belt between Mars and Jupiter; it measures about 135 
miles (217 kilometers) long and about 58 miles (94 kilometers) 
wide.  Kleopatra was discovered in 1880, but until now, its shape 
was unknown.

     "With its dog bone shape, Kleopatra is one of the most 
unusual asteroids we've seen in the Solar System," said Dr. Steven 
Ostro of NASA's Jet Propulsion Laboratory, Pasadena, CA, who led a 
team of astronomers observing Kleopatra with the 1,000-foot (305-
meter) telescope of the Arecibo Observatory in Puerto Rico.  
"Kleopatra could be the remnant of an incredibly violent collision 
between two asteroids that did not completely shatter and disperse 
all the fragments."

     The astronomers used the telescope to bounce radar signals 
off Kleopatra.  With sophisticated computer-analysis techniques, 
they decoded the echoes, transformed them into images, and 
assembled a computer model of the asteroid's shape.  The Arecibo 
telescope underwent major upgrades in the 1990s, which 
dramatically improved its sensitivity and made it feasible to 
image more distant objects.  

     These new radar images were obtained when Kleopatra was about 
106 million miles (171 million kilometers) from Earth.  Travelling 
at the speed of light, the transmitted signal took about 19 
minutes to make the round trip to Kleopatra and back.

     "Getting images of Kleopatra from Arecibo was like using a 
Los Angeles telescope the size of the human eye's lens to image a 
car in New York," Ostro said. 

     Kleopatra is one of several dozen asteroids whose coloring 
suggests they contain metal.  Kleopatra's strong reflection of 
radar signals indicates it is mostly metal, possibly a nickel-iron 
alloy.  These objects were once heated, melted and differentiated 
into structures containing a core, mantle and crust, much as the 
Earth was formed.  Unlike Earth, those asteroids cooled and 
solidified throughout, and many underwent massive collisions that 
exposed their metallic cores.  In some cases, those collisions 
launched fragments that eventually collided with Earth, becoming 
iron meteorites like the one that created Meteor Crater in 
Arizona.  

     "But we don't need to worry about Kleopatra -- it will never 
hit Earth," Ostro said.

      "The radar-based reconstruction of Kleopatra's shape shows 
the object's two lobes connected by a handle, forming a shape that 
resembles a distorted dumbbell, or dog bone," said Dr. R. Scott 
Hudson of Washington State University, Pullman, WA.  "The shape 
may have been produced by the collision of two objects that had 
previously been thoroughly fractured and ground into piles of 
loosely consolidated rubble.  Or, Kleopatra may once have been two 
separate lobes in orbit around each other with empty space between 
them, with subsequent impacts filling in the area between the 
lobes with debris."  

     "The radar observations indicated the surface of Kleopatra is 
porous and loosely consolidated, much like surface of the Moon, 
although the composition is different," said Dr. Michael Nolan of 
the Arecibo Observatory.   "Kleopatra's interior arrangement of 
solid metal fragments and loose metallic rubble, and the geometry 
of fractures within any solid components, are unknown. What is 
clear is that this object's collision history is extremely 
unusual."

     "It is amazing that nature has produced a giant metallic 
object with such a peculiar shape," said Ostro.  "We can think of 
some possible scenarios, but at this point none is very 
satisfying.  The object's existence is a perplexing mystery that 
tells us how far we have to go to understand more about asteroid 
shapes and collisions."

     The team's findings will appear in the May 5 issue of the 
journal Science.  Ostro's team includes Hudson; Nolan and Jean-Luc 
Margot of the Arecibo Observatory; Dr. Daniel Scheeres of the 
University of Michigan, Ann Arbor; Dr. Donald Campbell of Cornell 
University, Ithaca, N.Y; Dr. Christopher Magri of the University 
of Maine at Farmington; and Jon Giorgini and Dr. Donald Yeomans of 
the Jet Propulsion Laboratory.

     The Kleopatra images are available at:

              http://www.jpl.nasa.gov/pictures/kleopatra

     The Arecibo Observatory is part of the National Astronomy and 
Ionosphere Center, operated by Cornell University for the National 
Science Foundation.  The Kleopatra radar observations were 
supported by NASA's Office of Space Science, Washington, DC.  JPL 
is managed for NASA by the California Institute of Technology in 
Pasadena.

                                 -end-