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Thursday, 26 October, 2000, 14:30 GMT 15:30 UK
Four new moons found circling Saturn
Saturn Nasa
The ringed planet now has 22 known moons
By BBC News Online science editor Dr David Whitehouse

Saturn has become the planet with the greatest number of known moons, 22, following the discovery of four new satellites around it.

Moon Eso
Discovery image of one of the new moons
The four, faint bodies were detected during the past few months by several telescopes around the world. Further studies in the next few months will establish the satellites' precise orbits around the ringed planet.

They are classified as irregular moons and are thought to be captured asteroids.

Astronomers have several more moons of Saturn awaiting confirmation.

Faint and moving

The first two moon candidates were spotted using the European Southern Observatory's telescope in Chile. Images taken on 7 August revealed two, faint, moving objects near the glare of brilliant Saturn that could be new satellites.

Moon Eso
New moon: Three images of one satellite side-by-side
Then, on 23 September, a team of astronomers were observing at the Canada-France-Hawaii telescope on Mauna Kea in Hawaii. They found the two objects that had been discovered in Chile, and also two more.

Orbital calculations suggest that the bodies are not foreground asteroids, although this possibility cannot be ruled out.

Astronomers say that several months of further observations will be required to firmly establish the orbits of these objects. The studies should be accomplished before the planet disappears behind the Sun in March 2001.

More possible moons

The new moons are classified as irregular because they are far from their parent planet and were most likely captured after the planet formed.

In contrast, regular moons of the giant planets, which usually have nearly circular equatorial orbits close to the planet, are thought to have formed out of a disc of dust and gas that surrounded each planet as it formed.

Saturn's only previously known irregular satellite Phoebe was discovered in 1898. Jupiter has nine irregular moons (one of which was discovered last year), while Neptune has two, and Uranus five.

With these new discoveries, Saturn now has 22 known moons, one more than Uranus. The new moons of Saturn have diameters ranging from 10-50 km (5-30 miles), in line with the sizes of other irregular moons.

Saturn may have even more moons. Astronomers have found several other objects that are now being tracked to establish their orbits.

The discovery was made by an international team of astronomers at the Observatoire de la Cote d'Azur; McMaster University, Canada; the Harvard-Smithsonian Center for Astrophysics, US; and Cornell University, US.

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See also:

23 Jul 00 | Sci/Tech
New moon found circling Jupiter
28 Jul 99 | Sci/Tech
Two more moons for Uranus
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