Epimetheus taken on Mar. 30, 2005 by Cassini from a distance of 74,782 km.


South polar region of Epimetheus taken on Dec. 3, 2007 by Cassini from a distance of 37,400 km. The view shows what might be the remains of a large impact crater covering most of this face, and which could be responsible for the somewhat flattened shape of the southern part of Epimetheus. Also visible are two types of terrain: darker, smoother areas, and brighter, slightly more yellowish, fractured terrain. One interpretation of this image is that the darker material evidently moves down slopes, and probably has a lower ice content than the brighter material, which appears more like bedrock. Nonetheless, materials in both terrains are likely to be rich in water ice.

Epimetheus is an inner moon of Saturn. It was discovered in 1980 from photos taken by Voyager 1 and is also known as Saturn XI.

Epimetheus is located between the F- and G-rings (see Saturn rings) and shares the same orbit as Janus. Normally separated by about 50 kilometers, every 4 years these two satellites approach each other, exchange a small amount of momentum, and swap places. It is possible that they formed from the break-up of a single parent object.


The surface of Epimetheus reveals a number of valleys, grooves, and ridges, and extensive cratering, with several craters more than 30 kilometers (19 miles) in diameter.


discovery 1980, R. Walker et al,
Voyager 1 data
semimajor axis 151,410 km (94,110 miles)
diameter 135 × 108 × 105 km
(89 × 67 × 65 miles)
mean density 0.7 g/cm3
escape velocity 0.032 km/s (115 km/h, 72 mph)
orbital period 0.694 days (16 hr 39 min)
orbital eccentricity 0.010
orbital inclination 0.35°
axial period 0.694 days (synchronous)
visual albedo 0.5