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Named for a giant of Greek myth, Enceladus' diameter of some 500 km is significant, but not gigantic (it is just ten percent that of Saturn's largest moon, Titan). This moon follows a close orbit around Saturn, only about twice as far from the planet as the outer edge of its most prominent rings. Of the major moons of Saturn, only Mimas pursues a closer orbit around the ringed planet (though there are also many minor moons in this inner region).
Enceladus takes a little under 33 hours to complete a circuit of Saturn, and its orbit is synchronous, meaning that, like Earth's Moon, it always shows the same face to its parent planet. A slight eccentricity in its orbit means that Enceladus is subject to stress and deformation, and the resulting heating generates the energy that drives the moon's active geology. One noticeable result of this is that Enceladus generates its own minor ring of Saturn. The E Ring, a tenuous and hazy outer ring, is composed of particles blasted into space from the surface of Enceladus.
In appearance Enceladus is a gleaming white globe, with a surface entirely covered by thick ice. The icy surface is not smooth, but is speckled by craters, and shows long fractures, grooves and ridges across its surface. This patterning is especially strong in the southern polar regions, where four deep parallel fissures scar the surface with a tinge of greenish ice, the so-called 'tiger stripes'. Deep below the surface of Enceladus - generally at least thirty kilometres under the ice - lies a subsurface ocean. This ocean is at its deepest under the tiger stripes, and its content is forced out into space through the fissures in a spray of salt-laden ice.
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