|
NEW SCIENTIST
The Cassini space probe is set to meet Phoebe, the loneliest of Saturn's moons, which may be a pristine ice-world captured from the outer reaches of the Solar System.
The encounter, at 1930 GMT on Friday, will be the first close-up view Cassini gets of any part of the Saturn system. However, Phoebe is an outsider. It orbits 13 million kilometres from Saturn, much further out than any other major moon. Moreover, it is the only one to orbit backwards.
Because of these odd characteristics, astronomers think that Phoebe did not form like the other moons, from a primordial disc of material gathered around Saturn.
"We don't believe that Phoebe is a native of the Saturn system," says Carolyn Porco of the University of Arizona, head of the Cassini imaging team.
Instead, this 220 kilometre body probably once wandered the Solar System until was captured by Saturn's gravity field. Astronomers had thought it was most likely to be an asteroid, but five years ago they found evidence for ice on the moon's surface. That makes it less like a rocky asteroid and more like a comet.
SEE FULL TEXT
|