Atlas, in astronomy, one of the named moons, or natural satellites, of Saturn. Also known as Saturn XV (or S15), Atlas is a small, irregularly shaped (nonspherical) body measuring about 25 mi (40 km) by 12.5 mi (20 km); it orbits Saturn at a mean distance of 85,544 mi (137,670 km), and has an orbital period of 0.6019 earth days—the rotational period is unknown but is assumed to be the same as the orbital period. Atlas was discovered by Richard J. Terrile in 1980 from photographs taken by Voyager 1 during its flyby of Saturn. Atlas is probably a shepherd satellite (a moon that limits the extent of a planetary ring through gravitational forces) of Saturn's A ring.
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