Little is yet known about the nature of the new satellites, which were observed with the Canada-France-Hawaii Telescope atop Mauna Kea, Hawaii, and the 5-meter Hale Telescope on Palomar Mountain, California. Astronomers have not ruled out, however, that they may be members of a family of massive icy bodies called Centaurs. Being denizens of the cold outer fringes of the solar system, Centaurs are thought to comprise a swarm of icy asteroids, each akin to a giant comet nucleus.

The discovery of the first two new satellites this year designated S/1999 U 1 and S/1999 U 2 was a cooperative effort by team leader Brett Gladman of the Observatoire de la Cote d'Azur, Philip Nicholson and Joseph Burns of Cornell University, J. J. Kavelaars of McMasters University, and Matthew Holman of the Smithsonian Astrophysical Observatory. Holman detected the third satellite, S/1999 U 3, on his own while reducing data gathered during an earlier observing run for S/1999 U 1 and U 2.

Discovering these small satellites, whose average diameter is between 10 and 30 kilometers, from a distance of over 1.7 billion miles would have once been an impossible dream for astronomers using photographic plates. Even the most sensitive photograpic emulsions could only reveal objects as faint as about 20th magnitude. The latest generation of CCD cameras, however, enables them to look at fainter objects (24th magnitude) in a more unrestricted field of view.

If these truly are Urnaian satellites -- as Gladman suspects they are -- it will take about two more years to fully establish their orbits. Unfortunately, their observing window is beginning to narrow. In early January, Uranus moves too near the Sun and soon thereafter goes behind it. Therefore, says Gladman, "The next important thing to do is to get observations now in order to predict their [the satellites] positions next spring."