Saturn's moon Phoebe may be captured planetoid
It came from the Kuiper belt
By Simon Sharwood • In Science • At 22:53 GMT 26th April 2012
New analysis of images of Phoebe, one of Saturn's many moons, suggests it may be have started life as a planetoid in the Kuiper belt.
A paper in the April issue of Icarus suggests that after study with what NASA describes as “data from multiple spacecraft instruments and a computer model of the moon's chemistry, geophysics and geology” boffins reached the conclusion that Phoebe is a “remnant planetary building block.”
One telltale sign is the moon's shape, visible at right. "From the shape seen in Cassini images and modeling the likely cratering history, we were able to see that Phoebe started with a nearly spherical shape, rather than being an irregular shape later smoothed into a sphere by impacts," said Peter Thomas, a Cassini team member and co-author of the study. That heat may have come from radioactive elements which generated internal heat and helped the object to form. Internal warming may, the paper says, account for water signatures found by Cassini, as Phoebe may once have been warm enough to host liquid water.
Other evidence for the theory includes Phoebe's density, which is close to that of Pluto and therefore hints at similar origins. Throw in the fact that Phoebe orbits backwards and scientists feel it may have been captured by Saturn's gravity, rather than the process that caused its other moons to form. ®