Atlas (moon)

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Atlas
Cassini Atlas N00084634 CL.png
Photo taken by Cassini on June 12, 2007, showing Atlas as seen from above its south pole
Discovery
Discovered by Terrile, Voyager 1
Discovery date October, 1980
Designations
Pronunciation /ˈætləs/
Alternative names Saturn XV
Adjective Atlantean
Orbital characteristics[1]
Epoch December 31, 2003 (JD 2453005.5)
Mean orbit radius 137670±10 km
Eccentricity 0.0012
Orbital period 0.6016947883 d
Inclination 0.003°±0.004°
Satellite of Saturn
Physical characteristics
Dimensions 40.8 × 35.4 × 18.8 km [2]
Mean radius 15.1±0.9 km [2]
Volume ≈ 14400 km3
Mass (6.60±0.45)×1015 kg[2]
Mean density 0.46±0.11 g/cm³[2]
Equatorial surface gravity 0.0002–0.0020 m/s²[2]
Escape velocity ≈ 0.0062 km/s
Rotation period synchronous
Axial tilt zero
Albedo 0.4
Temperature ≈ 81 K

Atlas is an inner satellite of Saturn.

Atlas was discovered by Richard Terrile in 1980 (some time before November 12) from Voyager photos and was designated S/1980 S 28.[3] In 1983 it was officially named after Atlas of Greek mythology, because it "holds the rings on its shoulders" like the Titan Atlas held the sky up above the Earth.[4] It is also designated Saturn XV.

Atlas is the closest satellite to the sharp outer edge of the A ring, and was long thought to be a shepherd satellite for this ring. However, now it is known that the outer edge of the ring is instead maintained by a 7:6 orbital resonance with the larger but more distant moons Janus and Epimetheus.[5] In 2004 a faint, thin ring, temporarily designated R/2004 S 1, was discovered in the Atlantean orbit.[6]

High-resolution images taken in June 2005 by Cassini revealed Atlas to be have a roughly spherical centre surrounded by a large, smooth equatorial 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. In fact, the size of the equatorial ridge is comparable with the expected Roche lobe of the moon. This would mean that for any additional particles impacting the equator, the centrifugal force will nearly overcome the tiny Atlantean gravity, and they will likely be lost.[5]

Atlas is significantly perturbed by Prometheus and to a lesser degree by Pandora, 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. Since the orbits of Prometheus and Pandora are chaotic, it is suspected that Atlas's may be as well.[1]

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