Atlas is aninner satellite ofSaturn which was discovered byRichard Terrile in 1980 fromVoyager photos and was designatedS/1980 S 28.[5] In 1983 it was officially named afterAtlas ofGreek mythology, because it "holds the rings on its shoulders" like theTitan Atlas held the sky up above theEarth.[6] It is also designatedSaturn XV.
Atlas is the closest satellite to the sharp outer edge of theA ring, and was long thought to be ashepherd satellite for this ring. However, now it is known that the outer edge of the ring is instead maintained by a 7:6orbital resonance with the larger but more distant moonsJanus andEpimetheus.[7] In 2004 a faint, thin ring, temporarily designatedR/2004 S 1, was discovered in the Atlantean orbit.[8]
High-resolution images taken in June 2005 byCassini revealed Atlas to have a roughly spherical centre surrounded by a large, smoothequatorial ridge. The most likely explanation for this unusual and prominent structure is that ring material swept up by the moon accumulates on the moon, with a strong preference for the equator due to the ring's thinness. The size of the equatorial ridge is comparable with the expectedRoche lobe of the moon, which means that for any additional particles impacting the equator, thecentrifugal force will nearly overcome Atlas's tiny gravity, and they will probably be lost.[7]
Atlas is significantly perturbed byPrometheus and to a lesser degree byPandora, leading to excursions in longitude of up to 600 km (~0.25°) away from the precessing Keplerian orbit with a rough period of about 3 years. Because the orbits of Prometheus and Pandora are chaotic, it is suspected that Atlas's may be as well.[2]
^Calculated from the standard gravitational parameterGM =(3.664±0.028)×10−4 km3·s–2 given by Lainey et al. (2023), divided by thegravitational constantG =6.6743×10−2 km3·kg–1·s–2.[4]
