Saturn Swarming with Satellites
Saturn has again taken the lead as the planet with the greatest number of known satellites, following the discovery of at least 4 additional moons of that planet. The announcement today in Pasadena California at a meeting of the Division for Planetary Sciences of the American Astronomical Society. was made by an international team of astronomers including: Brett Gladman, Jean-Marc Petit, and Hans Scholl of the Observatoire de la Cote d'Azur; JJ Kavelaars of McMaster University, Canada; Matthew Holman and Brian Marsden of the Harvard-Smithsonian Center for Astrophysics; and Philip Nicholson and Joseph A. Burns of Cornell University. Four faint bodies were spotted during the last two months at several telescopes around the world. Orbital calculations indicate that the objects are almost certainly new satellites of the giant planet.

The first two moon candidates, details of which are described on an Oct. 26th electronic circular of the International Astronomical Union (IAU), were spotted using the European Southern Observatory's 2.2m telescope in Chile. Upon analyzing the images taken August 7th 2000 Gladman (who works for the French Centre National de Recherche Scientifique) realized that two faint moving objects he uncovered near the glare of brilliant Saturn could very well be new satellites of that planet.

On September 23rd and 24th, Gladman and Kavelaars were observing at the Canada-France-Hawaii 3.5-m telescope on Mauna Kea (Hawaii). In a more extensive search, they recovered the two objects discovered in Chile, and produced two more candidates (announced on a second IAU Circular on Oct 26th). Working as fast as the images came off the telescope, they were able to alert other teams of astronomers of the discoveries.

Additional confirming observations over the next few days came from R.L. Allen (Univ. of Michigan) at the 2.4-m MDM telescope in Arizona, C. Hergenrother and S. Larson at the Steward Observatory's 1.5-m telescope also in Tucson, and A. Doressoundiram and J. Romon at the ESO New Technology Telescope in Chile (just beside the 2.2m telescope on which the first two were discovered).

The orbital calculations by Brian Marsden developed for the IAU circulars prove that these objects cannot be foreground asteroids. Although it is currently impossible to prove that these are not comets passing fortuitously near Saturn, previous experience has shown that this is highly unlikely. Several months of continued observation will be required to firmly establish the orbits of these objects; these should be accomplished before the planet disappears behind the Sun in March 2001.

These moons are what astronomers refer to as `irregular' moons because they are far from their planet and were likely captured into orbit after the planet formed. In contrast, the `regular' moons of the giant planets, which commonly have nearly circular equatorial orbits nested close to the planet, are thought to have formed out of a disk of dust and gas that surrounded each planet as it formed. Saturn's only previously-known irregular satellite Phoebe was discovered in 1898 by W. Pickering at a Peruvian observatory. In contrast Jupiter has nine irregulars (one of which was discovered last year), Neptune two, and Uranus five (also discovered by this team, in 1997 and 1999). Saturn's total count of 22 moons now surpasses that of Uranus (with 21). The new moons of Saturn have diameters ranging from 10-50 kilometers (about 5-30 miles), in line with the sizes of other irregular moons.

The team has several other satellite candidates that are being tracked in order to see if they might also be satellites. It appears that there is a rich system of small distant moons swarming around the beautiful `ringed planet'.

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