Discoverer

J. Palisa - 1880

Diameter (km)

217 x 94 x 81

Mass (kg)

?

Rotation period (hrs)

5.385

Orbital period (yrs)

?

Semimajor axis (AU)

2.79178

Orbital eccentricity

0.25328

Orbital Inclination (deg)

13.14126

Albedo

0.12

Type

M

Named for the Egyptian queen (69-30 B.CJ, famed as mistress of Julius Caesar and of Mark Antony. Named by the Vienna astronomers.

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 217 kilometers long and about 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 in the solar system. 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 Arecibo radio 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 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.

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.

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. 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.

Images of Kleopatra

Asteroid's rotation.

Each quadrant shows Arecibo radar images from one date (top), corresponding images calculated from the shape model (middle), and corresponding plane-of-sky views of the model (bottom). Each scale bar is 100 km long.

Comparison of 216 Kleopatra & 90 Antiope

Antiope (top) is a double asteroid, in contrast to Kleopatra (bottom) which is a single connected body.