Enceladus & Iapetus
Some of the interesting variety among Saturn's many known icy satellites is
revealed in these Voyager 2 images. Enceladus' bright, relatively uncratered
terrain is coated with water ice. The smooth areas suggest that internal
heating has melted portions of the surface, possibly even leading to
"eruptions" that feed Saturn's tenuous E ring.
Iapetus, on the other hand,
has a leading face as dark as asphalt, while its trailing face is six
times brighter. The dark side is presumably some type of carbon-based material,
but was it swept up as the moon orbited Saturn, or did it rise up from the
moon's interior? Each of these theories has its scientific proponents.
Resolution of this and many other scientific questions will likely require
careful analysis of data to be provided by the Cassini/Huygens mission. (P-46656)