WILLIAM & DEBORAH HILLYARD
Mimas orbits Saturn once every 0.942422 days at a distance of 185,520 km (c. 115,280 miles).  It is about 400 km (250 miles) in diameter. 

The first thing one notices in pictures of Mimas is the enormous crater Herschel, named after William Herschel who discovered it in 1789.  The crater is huge; 130 km (81 miles) across.  The central peak in the crater is about 6 km (3.75 miles) high; mount Everest is 8.8 km (5.5 miles) high.  Remember; this is on a moon that is only about 400 km across; Earth is about 32 times bigger!  In fact, Mimas is not spherical, but is more of an ellipsoid about 415 km by 381 km (260 by 238 miles).  Composed primarily of water ice, and a small amount of rock, Mimas' density is quite low, being little more than 20% Earth's density. 

Although none are nearly as large as Herschel, the entire surface is covered in craters.  There is little evidence of internal activity so that new impacts overlay or completely destroy older craters

Mimas is responsible for a large gap called the Cassini Division in Saturn's ring system.  It is a zone where particles would have a 2:1 resonance with Mimas, so would have been disrupted on a regular basis thus, over millions of years, pushing them out of the resonance, creating the gap. 
This image shows Mimas behind Saturn's F ring.  Taken by the Cassini probe in January 2008. 
Image of Mimas taken by the Cassini probe on November 19, 2016 from approximately 85,000 km (53,000 miles) away. 
This image of Mimas was taken by Cassini on Feb. 13, 2010, from a distance of approximately 70,000 kilometers (43,000 miles) from Mimas.
Here, one can see craters overlapping one another, smaller craters inside larger ones, and some with evidence of debris inside them.  This debris may be the result of landslides caused by nearby collisions.

Solar System -

Saturn's Moons

Mimas

Credit: NASA/JPL/Space Science Institute (Cassini)
This is a false-color image of the Herschel Crater taken by Cassini on its closest encounter with Mimas on February 13th 2010 from a distance of about 9,500 km. 
Saturn's moons are grouped as follows.  Select to see details of the moon or the group of moons:


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