Son of Chiron: now showing in space.

It may sound like one of Godzilla's adversaries, but Son of Chiron is actually the nickname of a puzzling new object that astronomer David L. Rabinowitz discovered in the orbital range of Saturn. "We're stumped by it," says Tom Gehrels, director of the University of Arizona Spacewatch team in Tucson. "No one that I know of really understands what it is."

Rabinowitz, a member of the Spacewatch team, first spied the object Jan. 9, using a 0.9-meter telescope on Arizona's Kitt Peak. The initial report of this sighting and several subsequent observations by other astronomers appeared in an International Astronomical Union circular distributed Jan. 23.

So far, astronomers know little about the object, officially dubbed 1992 AD, except its size (about 200 kilometers in diameter), its elliptical path (which carries it between the orbits of Saturn and Neptune) and its color (redder than any known asteroid or comet).

This makes it just the second large, asteroid-like object found in that part of the solar system. Astronomer Charler Kowal discovered the first, Chiron, in 1977 as it circled the sun between the orbits of Saturn and Uranus. Ten years later, when Chiron swung closer to the sun, astonished scientists observed a comet-like halo, or coma, around its head (SN: 4/21/90. p.244). A coma suggests the existence of surface ice that begins to vaporize as it nears the sun.

Although astronomers have detected no coma around Son of Chiron, several would not be surprised if one appeared. "When Chiron was newly found there was no halo," Gehrels says. "Everybody looked for it very carefully. It was only years later that it appeared."

James V. Scotti -- another member of the Spacewath team, which uses an automated telescope to scan the night sky -- adds that a coat of ice probably sheathes many objects in the solar system's cold outer reaches. "Pluto, I think if you brought it close to the sun would look like a comet," he says. "A big one, by the way."

Because the object came nearest to the sun last May, Brian G. Marsden of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., says, "If it's going to show a coma, now is the time to look"--since it may still be warm enough to emit a cloud of water vapor.

Although they can offer some theories, astronomers frankly admit they have no idea where Son of Chiron originated. But whatever its origins, most astronomers agree that Chiron and Son of Chiron represent only a fraction of the enigmatic asteroid-like bodies that await discovery in the outer solar system.

Astronomers expect that as they discover more such objects, they will better understand the early makeup of the outer solar system and how these materials coalesced to form the planets. In the meantime, Gehrels says his team is enjoying all the ruckus over the new find. "We're having a filed day with it," he laughs.