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Enceladus[ensel´udus] Pronunciation Key, in astronomy, one of the 18 named moons, or natural satellites, of Saturn. Also known as Saturn II (or S2), Enceladus is 310 mi (500 km) in diameter, orbits Saturn at a mean distance of 147,900 mi (238,020 km), and has equal orbital and rotational periods of 1.37 earth days. It was discovered in 1789 by the English astronomer Sir William Herschel. Enceladus has the highest reflectivity (almost 100%) of any body in the solar system. Its surface, believed to be dominated by fresh, clean ice, is marked by few craters, smooth plains, and extensive fissures and ridges. Observations indicate that Enceladus has had five distinct geologic periods. The fresh surface suggests relatively recent volcanism, caused perhaps by tidal forces exerted by Saturn and the moon Dione, with which Enceladus forms a satellite pair (that is, they interact gravitationally).
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