Donald Savage

Headquarters, Washington, DC

(Phone: 202/358-1547)

Jane Platt

Jet Propulsion Laboratory, Pasadena, CA

(Phone: 818/354-0880)

RELEASE: 00-74

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

“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

“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 in