Round? Not really...

Caption NASA originale:"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. The moon's equatorial dimension is nearly 10% larger than the polar one due to the satellite's rapid rotation. This view shows principally the leading hemisphere on Mimas. Mimas' largest crater, Herschel (130 Km, 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 only 5° 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 approx. 916.000 Km (about 569.000 miles) from Mimas. Resolution in the original image was 5 Km (about 3 miles) per pixel".