Image of the Day: Saturn's "Death Star Moon" --Hosts One of the Largest Impact Craters in the Solar System
Saturn's moon Pandora looms behind Mimas, the "Death Star moon," in this photo from NASA's Cassini mission that highlights Mimas' huge 86 mile (139 kilometer) wide circular Herschel Crater --the scar of a violent, giant impact from the past. The diameter of the crater is about one-third that of the entire moon. The walls of the crater are about 5 kilometers (3 miles) high, and parts of the floor are approximately 10 kilometers (6 miles) deep. The impact that made this crater must have nearly shattered Mimas: fractures can be seen on the opposite side of Mimas created by shock waves from the impact on the moon's body. The impact is similar (but smaller) to the mysterious object that created a Pacific-sized impact on Jupiter in July 2009.
Mimas is 246 miles (or 396 kilometers) wide and is massive enough for hydrostatic equilibrium to dominate its shape. Hydrostatic equilibrium causes planetary bodies to form into a sphere. For smaller Pandora, however, its mass isn't large enough to create a gravitational field strong enough to achieve hydrostatic equilibrium -- its internal structure resists becoming a sphere, so it remains elongated like a potato, measuring 50 miles (or 81 kilometers across) at its longest axis
The Daily Galaxy via JPL/NASA