Franck Marchis, Daniel Hestroffer and their colleagues used adapted optics on the telescope on Oct. 25 to look directly at Kleopatra, a Main belt body with an elongated orbit that passes between Mars and Jupiter. They say the session showed that Kleopatra is comprised of two similarly sized lobes, neither of which is small enough to be called a moon.

If the finding, reported in a recent issue of the International Astronomical Union's Central Bureau for Astronomical Telegrams, is confirmed, the Kleopatra pair might not be the first of its kind -- depending upon the separation between the "twins."

In 1989, Jet Propulsion Laboratory asteroid tracker Eleanor Helin discovered a similar binary system called 4769 Castalia, in which the two pieces are stuck together by gravity as if kissing. That asteroid or pair is much smaller in diameter (about a mile across) and has been studied extensively with radar.

Still, the Kleopatra pair could be part of a small class of binary bodies first thought to be singular and later discovered to be more complex. Other cases include asteroids with moons -- asteroid 243 Ida and its moon Dactyl, and asteroid 45 Eugenia, whose moon was reported in October to be photographed by an Earth-based telescope for the first time.

"We're quite confident that we have two lobes," said Hestroffer, an astronomer at the Paris Observatory's Institute for Celestial Mechanics. "As for separation, we're quite confident that it's 0.125 arcseconds." That would put the center-to-center distance between the two objects at 62 miles (100 kilometers).

The Kleopatra pair, currently near the point in its orbit that comes closest to the sun, includes two low-density objects with a 5.4-hour rotation period.

The astronomers are uncertain of the diameter of the two objects and are waiting for more data, including observations made with radar, Hestroffer said.

The existence of asteroid binaries raises questions about the evolution of the solar system relics. Some are thought to have been knocked from other larger bodies, others might be congealed piles of space rubble left over from the initial formation of the solar system 4.6 billion years ago.

"Now there is also a lot of work to see how long can such a system be stable, how can it be formed," Hestroffer said. The Kleopatra pair is too dense to be a rubble pile, he said.

Brian Marsden, who puts out the Central Bureau for Astronomical Telegrams and is director of the Minor Planet Center in Cambridge, Mass., said the European group's report was credible enough to publish in the circular but ideally should be confirmed. He questioned the idea that the objects are separated by any space at all, in which case they might be classified as a "contact binary" like Castalia rather than a "near-contact binary," as Hestroffer suggested.

Other astronomers have reported Kleopatra as a double object in the past, but those findings never were confirmed and relied on a different observational technique, Marsden said.

For instance, the Hubble Space Telescope photographed Kleopatra but failed to "confirm or rule out the binary nature" of the object, Hestroffer said.

The whole area of binary asteroids is "very touchy," Marsden said, because some of the earliest reports failed to pan out in the long run.

When Galileo directly imaged Dactyl orbiting Ida six years ago, the concept of asteroid binaries gained some credibility, he said.

"There seemed to be no doubt about it from Galileo," he said.

Still Marsden wasn't sure that the concept was "100 percent proven," he said. "Maybe a good 80 percent."