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Mimas


Mimas is one of the innermost moons of Saturn. The surface is icy and heavily cratered. Mimas has a low density and consists mostly of ice. Because Mimas has such a low temperature (about -200 degrees C), the impact features may date back to the time of the moon's creation.

One of the craters, named Herschel (after the discoverer of Mimas, William Herschel, in 1789), is surprisingly large in comparison to the size of the moon. The crater is 130 kilometers wide, one-third the diameter of Mimas. Herschel is 10 kilometers deep, with a central mountain almost as high as Mount Everest on Earth. This central peak rises 6 kilometers above the crater floor. This impact probably came close to disintegrating the moon. Traces of fracture marks can be seen on the opposite side of Mimas.

Although Mimas is heavily cratered, the cratering is not uniform. Most of the surface is covered with craters greater than 40 kilometers in diameter but in the south polar region, craters greater than 20 kilometers are generally lacking. This suggests that some process removed the larger craters from these areas.


Orbital Distance:   185,500 km (average)
Eccentricity:       0.020
Local Year:         0.942 days (22h 37m 5s)
Orbital Velocity:   14.324 km/s
Inclination:        1.53°
Local Day:          0.942 days (22h 37m 5s)
Axial Tilt:         n/a

Diameter:           398 km
Composition:        Water ice and small amounts of rock
Density:            1.15 g/cm3
Mass:               3.80 x 1016 tonnes (6/million earths)
Gravity:            0.007 G
Escape Velocity:    0.16 km/s
Area:               500,000 km2
Surface Material:   Mostly H2O ice
Atmosphere:         None
Pressure:           None
Albedo:             0.50
Temperature:        -200°C

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