DALLAS -- Astronomers have discovered an object on the fringe of the solar system, possibly a gigantic comet, farther from the sun than the outermost planets.
It is the most distant body detected in the solar system since Pluto's discovery in 1930.
"If confirmed, it's fair to say that for astronomy this easily could be the discovery of the year, if not the decade," said Alan Stern, an astronomer at the Southwest Research Institute in San Antonio, Texas. "In my opinion it is as momentous as the discovery of the first asteroid. This is a major piece of the architecture of the solar system now falling into place."
"As far as astronomical events go, I think it's very exciting," said Harold Weaver, a Johns Hopkins University astronomer studying comets with the Hubble Space Telescope. "If they really do confirm it's that far out, then it's a new member of the solar system. It's a substantial object. Heck, we go a pretty long time between new discoveries like this."
Astronomers David Jewitt of the University of Hawaii and Jane Luu of the University of California-Berkeley first sighted the object in the constellation Pisces on Aug. 30 with an 86-inch telescope at the Mauna Kea observatory in Hawaii. Repeated viewings were recorded on the next two nights.
The first official word of the discovery was circulated this week in a bulletin from the International Astronomical Union bureau in Cambridge, Mass.
"Probably the best guess is that it's the nucleus of a giant comet," said Steve Maran, an astronomer at NASA's Goddard Space Flight Center in Greenbelt, Md.
Scientists have not yet been able to compute the orbit of the object, designated 1992 QB1. But it may belong to the so-called Kuiper Belt of comets suspected to lurk outside the orbit of Neptune, at this time the farthest planet from the sun.
"We suspect this is the first detected member of the Kuiper Belt," Mr. Jewitt said Tuesday in a telephone interview. The search for such an object has been under way for six years, he said.
"We hope, that by studying this object and others we find in the future that are similar to it, to get observational information about the early solar system and how the planets formed around the sun," he said.
Experts think comets that regularly visit the inner solar system, such as Halley's, must originate in the Kuiper Belt, hypothesized the astronomer Gerard Kuiper in 1951.
The new object seems to be intermediate in size, much smaller than the icy planet Pluto but perhaps 20 times the size of an ordinary comet.
"Right now we don't know if it's a comet in the Kuiper Belt or an object on its way in toward the sun," said Paul Weissman, a comet expert at the Jet Propulsion Laboratory in Pasadena, Calif. "But it's starting to lend credence to the fact that there really is a Kuiper Belt."
With current information, it's not possible to say exactly how large the object is, how far away it is from the sun, or even in which direction it is orbiting, said Brian Marsden, associate director for planetary sciences at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.
Mr. Marsden, who issued the astronomical union bulletin, said preliminary analysis by Mr. Jewitt and Ms. Luu indicates that the object is roughly 120 miles across, about one-10th to one-12th the size of Pluto. Mr. Marsden's calculations suggest that the object is now from 37 to 59 times farther from the sun than the Earth is. (The Earth-sun distance, about 93 million miles, is known as an "astronomical unit.")
The discovery of one faint, relatively large object in the Kuiper Belt suggests that many smaller ones also exist, he said. "There's probably quite a lot of these things."
"This could be the dawn of a new age of outer solar system exploration," said Mr. Maran.
Mr. Stern, who last year proposed the existence of a thousand Pluto-size planets outside the known planets, said the discovery is evidence favoring that view.
"This is very strong circumstantial evidence that larger guys are out there," he said.
Mr. Marsden said it would be misleading to call these objects planets. "I don't know quite what to call them," he said. "We really need some new term for them."