A team of astronomers has used a mammoth radio antenna 1,000 feet (305 meters) across to collar a dog-bone-shaped asteroid the size of New Jersey.

The team used the Arecibo Observatory in Puerto Rico to bathe the asteroid known as 216 Kleopatra in radar signals. Analysis of the echoes from those signals allowed them to then build up a three-dimensional computer model of the metallic rock.

"There is nothing like this that we know of. Its a unique object," said Steven Ostro, of NASAs Jet Propulsion Laboratory (JPL), who led the team of astronomers. "Its the most unusual shape that we have ever seen and its fantastic that it exists, and its not something that is light-years away in a distant galaxy. Its right here, within the orbit of Jupiter."

"We just stood there and stared at the screen. What the heck is this thing?"

The announcement is more than a scientific novelty: The radar models are also the first ever of any of the Main-belt asteroids that lurk between Mars and Jupiter.

"This is the first time we got enough images, and at a good enough resolution, to construct a three-dimensional model," said Ostro, adding that the first look at the images left the team dumbfounded.

"We just stood there and stared at the screen. What the heck is this thing?" Ostro said.

Astronomers discovered Kleopatra in 1880, but its exact shape has been largely unknown until now.

In 1980, an astronomer proposed the asteroid was dumbbell shaped, but successive attempts to image it in any detail, including with the Arecibo dish in 1985 and the Hubble Space Telescope in 1993, proved inconclusive.

Since then, Arecibo has undergone a major upgrade that improves its sensitivity, allowing it to hone in on objects like Kleopatra. The asteroid was approximately 106 million miles (171 million kilometers) from Earth when the images were acquired in November 1999. Ostro said he expects to produce similar models of other asteroids several times a year.

The object is 135 miles (217 kilometers) long and 58 miles (94 kilometers) wide. The model, the astronomers report, is accurate to within about 9 miles (15 kilometers).

The asteroids odd shape still stumps astronomers, who can only guess what sort of unusual impact history it must have undergone.

"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," said R. Scott Hudson, of Washington State University in Pullman, Washington. "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 team's findings will appear in the May 5 issue of the journal Science. Ostro's team included Hudson; Michael Nolan and Jean-Luc Margot of the Arecibo Observatory; Daniel Scheeres of the University of Michigan, Ann Arbor; Donald Campbell of Cornell University, Ithaca, New York; Christopher Magri of the University of Maine at Farmington and Jon Giorgini and Donald Yeomans of JPL.