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FOR IMMEDIATE RELEASEMay 4, 2000
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
The asteroid, named 216 Kleopatra, is a large object in the
main asteroid belt between Mars and Jupiter; it measures about
217 kilometers (135 miles) long and about 94 kilometers (58
miles) 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,
Calif., who led a team of astronomers observing Kleopatra with
the 305-meter (1,000-foot) 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 171 million kilometers (106 million miles) from Earth.
Traveling 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
"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:
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