Not Quite Round
Saturn's moon Mimas, whose low density suggests that it is primarily composed of ice, has a flattened or oblate shape reminiscent of Saturn's (see Saturn in Color ). The moon's equatorial dimension is nearly 10 percent larger than the polar one due to the satellite's rapid rotation. Mimas is 397 kilometers (247 miles) across.
This view shows principally the leading hemisphere on Mimas. Mimas' largest crater, Herschel (130 kilometers, or 80 miles wide), is centered roughly on the equator and can be seen here. North on Mimas is toward upper left.
The moon's oblateness is exaggerated by Cassini's viewing angle here -- the Sun-Mimas-spacecraft, or phase, angle was 5 degrees leaving a sliver of the moon's disk in shadow on the northwest limb.
The image was taken in visible light with the Cassini spacecraft narrow-angle camera on May 20, 2005, at a distance of approximately 916,000 kilometers (569,000 miles) from Mimas. Resolution in the original image was 5 kilometers (3 miles) per pixel. The image has been contrast-enhanced and magnified by a factor of two to aid visibility.