Twelve more moons for Saturn
From AFP
12jul01
AN international team of astronomers report today that they have spotted 12 more moons
orbiting Saturn, putting the ringed giant back ahead of Jupiter as the planet with the
most satellites.
The moonlets range from 32 kilometres to just 6 kms in diameter, they report in the
British weekly Nature.
That brings the unofficial count of Saturnian moons to 30, two more than the tally of
Jupiter, the biggest planet of our Solar System. The other behemoths, Uranus and Neptune,
have 21 and eight respectively.
The new moons were detected by a team in France, Canada and the United States, led by
Brett Gladman of the Cote d'Azur Observatory at Nice, southern France.
They believe that the discovery sheds light on the enigmatic source of Saturn's
"irregular" satellites -- small moons that follow large, eccentric orbits around
the great planet.
The conventional view about "irregulars" is that these were lonely bodies that
were wandering the heavens until, billions of years ago, they were sucked into a giant
planet's gravitational field, where they were captured for eternity.
In contrast, "regular" satellites are believed to have condensed from the same
cloud of gas and dust that formed their parent, and circle the planet close in, tracking
in neatly circular equatorial orbits.
Gladman's team say they were surprised to find that the 12 newly identified moons fall
into four "clusters," with three groups of satellites close to each other, and a
single one by itself.
This, they say, suggests the satellites were not sucked in from outside but were in fact
the result of some collision -- perhaps a comet that smacked into a larger moon, smashing
off fragments which in turn became circling captives.
The discoveries, if ratified by the International Astronomical Union (IAU), which also has
responsibility for naming newly identified bodies, are the latest in a spate of newly
identified moons over the past five years.
Since 1996, the number of solar system "irregulars" has nearly quadrupled, from
10 to 39.
The increase is explained by technical breakthroughs in scanning and data-analysing, in
which a terrestrial telescope is trained on an area of interest and computers then track a
bright object to see how it moves.
"The richness of the irregular satellite systems is yielding valuable insights into
the physical conditions and processes that occurred during the final stages of giant
planet formation," the researchers say.
Further improvements in detection, and the use of larger telescopes in the
eight-to-10-metre range -- several times bigger than the gear used in this survey -- is
bound to unveil more "irregulars" around all the giant planets, they predict.
Other participants in the study were from McMaster University at Hamilton, Ontaria; the
Harvard-Smithsonian Center for Astrophysics at Cambridge, Massachusetts; Cornell
University; the University of Arizona at Tucson; the Jet Propulsion Laboratory and the
University of Oslo.
Publication of the research follows an announcement by the same team last October that it
had found an initial batch of four satellites in August and September.
Eight more were then found until mid-February, just before Saturn moved behind the Sun,
temporarily disappearing from Earth-bound eyes.END OF REPORT
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