Phoebe: Comet Moon of Saturn
Was Saturn's moon, Phoebe, once a comet? Images from Cassini, taken when the spacecraft entered the neighborhood of Saturn, indicate that Phoebe may have originated in the outer solar system. Phoebe's irregular surface, retrograde orbit, unusually dark surface, assortment of large and small craters, and low average density appear consistent with the hypothesis that Phoebe was part of the Kuiper Belt of icy comets beyond Neptune before it was captured by Saturn. Visible in this image of Phoebe are craters, streaks, and layered deposits of light and dark material.
The image was taken from around 19,000 miles out from this 137-mile wide moon. Two weeks after taking the above image, Cassini fired its engines to decelerate into orbit around Saturn.
Image Credit: NASA/ESA/JPL/SSI