Calypso

Calypso is one of the smallest moons in the solar system 
(see saturn's moons index page). 

Dione

Dione is the densest of Saturn's moons. It is composed primarily of water ice but must have a considerable fraction of denser material like silicate rock.

The leading hemisphere is heavily cratered and uniformly bright. Like Callisto, the craters lack the high relief features seen on the Moon and Mercury.

   This is interpreted as follows: shortly after its formation Dione was active. Some processes resurfaced much of Dione leaving the pattern of streaks, probably on the whole surface. Later, after the internal activity and resurfacing ceased, a much less intense series of impacts (which left craters too small to be seen in Voyager's images) occurred. This was concentrated on the leading hemisphere and wiped out the streak patterns but left them intact on the trailing hemisphere.