Saturn is now on top as the planet with the most moons in its gravitational grasp.
An international team of 11 astronomers that scanned the gas giant's skies from August 2000 to February 2001 bestowed the title in an article published Wednesday in the journal Nature. The astronomers discovered 12 new Saturnine satellites, racking up its total to 30.
The evolution of gas giants
The 12 moons are unlike our Moon in any way. They are all very small, with radii ranging from 1.9 to 8 miles (3 km to 13 km), and all have large, eccentric orbits. This kind of swarming satellite is unique to the Gas Giants in our Solar System, therefore the scientists think their discoveries will be key in understanding the evolution of Saturn, the other large planets -- Jupiter, Uranus, and Neptune, and the solar system as a whole.
"We believe that these moons were captured by the friction from their passing through the thick gas environment of the young planet," said Brett Gladman, a collaborating astronomer from the Observatoire de la Cote d'Azur in Nice, France. "They are likely from a bigger body that was broken up."
The "bigger body" Gladman mentioned is thought to be one of a group of objects called planetesimals -- objects of our early solar system that orbited the Sun and eventually formed the unique cores of the gas giants. Once the planets were massive enough to have the gravity needed to pull the planetesimals away from the Sun, some of them became the precursors of the unique moons.
The evidence for this resides in the common orbits the moons follow. Although one of the new moons does travel by itself, the other eleven occupy one of only four orbital routes. This points easily to the planetesimal theory, yet the observations are still preliminary.
"We're hoping to determine the process of satellite accumulation, but there's not yet enough evidence to definitely say how these object got there," said William Gray, the project's software collaborator.
What do the scientists really know?
For now, the orbits of the moons, and their sizes are all that scientists can hope to really know. For each moon, three observations were made once an hour to find objects that were traveling with a speed relative to the mother planet: the definition of a moon.
"If you make one observation, it looks like a whole bunch of stars, but take one an hour later, and, hmm, it may look like one 'star' moved, and moved at the speed of Saturn," said Gray. "More observations firm up ideas of the moon's speed and where it is. It gets to a point that we're confident that we know these orbits."
More data will affirm these initial observations when the team does it all over again later this year, after Saturn stops hiding from their telescopes behind the Sun. If the moons are where the scientists predict they will be, they will earn the moons official names from the International Astronomical Union.
"When we observe them again, that will mean that we know what the orbital configuration is," said Gladman. "But I don't have many doubts that we'll be nailing them."
Confidence aside, scientists are still limited by their tools and subject matter. In this case, Saturn's designation as the most jeweled planet may prove rather arbitrary. In another article in today's Nature, astronomer Douglas Hamilton of the University of Maryland explains that for this reason Jupiter will probably come out on top.
"If somebody would do the same survey of Jupiter they would be able to see down to one kilometer, (0.62 mile) while they could only see down to four kilometers (2.5 miles) at Saturn. And at Jupiter, objects are brighter [because they are closer to the Sun] than at Saturn, so you can see more and more smaller objects there," Hamilton said.
A closer look
In 2004, the Cassini mission will be in orbit at Saturn. That mission team has agreed to take advantage of any opportunity that may present itself to observe any one of the twelve new moons, Hamilton said.
"If Cassini comes close to some of these objects, it may be able to take some pictures," Hamilton said. "We would expect them to bee irregular in shape. If they would turn out to be small spheres, that would be a surprise."
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