Newly discovered moon is circled; Uranus is in lower right. Credit: NASA/JPL

A new moon of the planet Uranus has been discovered and confirmed by a team of astronomers including Dr. Christophe Dumas of NASA's Jet Propulsion Laboratory, Pasadena, Calif.

This most-recently discovered natural satellite, named S/2001 U 1, brings the total number of confirmed uranian moons to 21. S/2001 U 1 and five others like it have very irregular, eccentric orbits that do not share the same orbital plane as the larger moons of Uranus. Ranging in size from 10 to 20 kilometers (about 6 to 12 miles), these moons are thought to be remnants of ancient collisions that occurred at the early stage of planetary formation.

"The irregular satellites like S/2001 U 1 are very difficult to find because they are faint and tend to be very distant from the planet," Dumas said. "It is hard to distinguish them from the background stars, and this requires special observing techniques. Because these objects formed far from the Sun, they are probably similar in composition to the most primitive objects of the solar system."

Identifying S/2001 U1 as a moon and mapping its orbit required intense effort and observation from several telescopes located in North and South America. It was first spotted by Drs. Matthew Holman of the Harvard-Smithsonian Center for Astrophysics, Cambridge, Mass., and J.J. Kavelaars, now at Dominion Astrophysical Observatory, Victoria, British Columbia, Canada, in August 2001 in images obtained at Cerro Tololo Observatory in Chile. Dumas and Dr. Phil Nicholson from Cornell University, Ithaca, N.Y., re-observed it from Palomar Observatory, near San Diego, Calif., a month later. The object was then followed from Chile again, using the 8-meter (26-foot) European Southern Observatory telescopes.

The discovery of the moon was a collaboration of 11 astronomers, led by Holman; Kavelaars; Dr. Brett Gladman, University of British Columbia, Vancouver, Canada; and Dr. Jean-Marc Petit, Observatoire de Besançon, Besançon, France.

JPL is a division of the California Institute of Technology in Pasadena.