The darkest moon is there...

A distant glimpse of Japetus reveals details within the dark terrain of the Cassini Regio, including an impact basin at top that is roughly 400 Km (about 250 miles) wide.
Researchers remain unsure about the mechanism that has darkened the Leading Hemisphere.
This view looks toward the Southern Hemisphere on the leading side of Japetus (1.468 Km, or about 912 miles across). North is up.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on April 4, 2006, at a distance of approx. 1,4 MKM (such as about 900.000 miles) from Japetus.
The image scale is roughly 9 Km (about 6 miles) per pixel.