Saturn is 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.
These were observed by an international team of astronomers¹ ,which include
researchers from the Observatoire de la Côte d’Azur (Département
Cassini, UMR CNRS), through the 3,6 m Canada-France-Hawaii Telescope (CNRS-CNRC-University
of Hawaii) and the 2,2 m telescope of the European Southern Observatory.
Orbital calculations indicate that the objects are almost certainly new
satellites of the giant planet. The announcement will be made on October
26, 2000 in Pasadena, California at a meeting of the Division for Planetary
Sciences of the American Astronomical Society.

The first two moon candidates were spotted through the European Southern
Observatory’s 2.2m telescope in Chile (ESO= While analyzing the images taken
on August 7, 2000, Brett Gladman (CNRS)) realized that two faint moving
objects he could see in the glare of Saturn could very well be new satellites.

On September 23 and 24, B.Gladman and JJ. Kavelaars observed Saturn at the
Canada-France-Hawaii 3.6-m Telescope (CNRS-CNRC – University of Hawaii).
They found once again the two objects discovered in Chile, and produced
two more candidates.

Additional observations, confirming previous discoveries, came over the
next few days from the 2.4-m MDM telescope in Arizona, the Steward Observatory’s
1.5-m telescope in Tucson, Arizona, and the ESO New Technology Telescope
in Chile.

Orbital calculations prove that these objects cannot be foreground asteroids.
However, it is highly unlikely that these are comets passing fortuitously
near Saturn. Several months of continued observation will be required to
firmly establish the orbits of these objects. This should be accomplished
before the planet disappears behind the Sun, in March 2001.

These moons are what astronomers refer to as `irregular’ satellites, because
they are far from their
planet and were most likely captured into orbit after the planet formed.
In contrast, the `regular’ moons of the giant planets, which usually have
near-circular orbits, were probably formed out of a disk of dust and gas
that surrounded each giant planet at the time of its formation.

Saturn’s only previously known irregular satellite was Phoebe. In contrast,
Jupiter has nine irregular satellites, Neptune two, and Uranus five (see
CNRS-Info n°378, October 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 to 50 kilometers, in line with the sizes of other irregular
moons.

The team has observed several other satellite candidates that are being
tracked in order to confirm their orbits. It appears that there is a rich
system of small distant moons swarming around Saturn.

This research project is supported by the "Incentive Concerted Action—Young
Researchers" of the Ministry of Research.

Information and images available at: http://www.obs-azur.fr/saturne

1 – This international team is made up of:
– Brett Gladman, Jean-Marc Petit, and Hans Scholl of the Observatoire de
la Côte d’Azur,
– JJ Kavelaars of McMaster University , Canada,
– Matthew Holman and Brian Marsden of the Harvard-Smithsonian Center for
Astrophysics,
– Philip Nicholson and Joseph A. Burns of Cornell University.

Researcher
Contact:
Brett Gladman
Observatoire de la Côte d’Azur
Tel: + 33 4 92 00 31 91
E-mail : gladman@obs-nice.fr

Press Contact:
Philippe Chauvin
Institut National des Sciences de l’Univers
Tel: + 33 1 44 96 43 36
e-mail: Philippe.Chauvin@obspm.fr