After a journey of nearly a billion miles and nearly seven years, the Cassini spacecraft began to produce even during the early phase of its approach to the planet Saturn. Its instruments probed the unusual moon Phoebe.

Discovered in 1898, Phoebe is some 140 miles in diameter and extraordinarily dark, reflecting less than 6 percent of the sunlight it receives. It orbits Saturn in a direction opposite to that of nearly all the planet’s 31 other discovered moons. Now, with the preliminary results from Cassini’s first look, it appears that the hypothesis that Phoebe is a “Centaur”—a body ejected from the Kuiper belt beyond Neptune and Pluto, and subsequently captured by Saturn’s gravitational attraction. This could prove quite important, since Kuiper belt planetesimals are considered to be frozen “time capsules,” the primordial remnants left over from the formation of the solar system.

Like Pluto and other Kuiper belt residents, Phoebe is “a comet-like mixture of water ice, rock, hydrated minerals and carbon-rich material.” Cassini also detected carbon dioxide ice, which has been found on Pluto, but never previously on small moons or asteroids.
(New Scientist)

–From the June 2004 Austin Review KB