Astronomy:Atlas (moon)

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Short description: Moon of Saturn
Atlas
Atlas color PIA21449.png
Color photo taken by Cassini on 12 April 2017
Discovery
Discovered byTerrile, Voyager 1
Discovery dateOctober, 1980
Designations
Designation
Saturn XV
Pronunciation/ˈætləs/
Named afterἌτλας Ātlās
S/1980 S 28
AdjectivesAtlantean /ætlænˈtən/[1]
Orbital characteristics[2]
Epoch December 31, 2003 (JD 2453005.5)
Mean orbit radius137670±10 km
Eccentricity0.0012
Orbital period0.6016947883 d
Inclination0.003°±0.004°
Satellite ofSaturn
GroupOuter shepherd moon of the A Ring
Physical characteristics
Dimensions40.8 × 35.4 × 18.6 km
(± 0.2 × 0.4 × 0.6 km)[3](p2)
Mean diameter29.8±0.4 km[3](p2)
Volume13950±50 km3[4](p4)
Mass(5.490±0.042)×1015 kg[lower-alpha 1]
Mean density0.3935±0.0033 g/cm3[4](p4)
0.0001–0.0017 m/s2[3](p3)
0.006 km/s at longest axis
to 0.009 km/s at poles
Rotation periodsynchronous
Axial tiltzero
Albedo0.4
Physics≈ 81 K


Atlas is an inner satellite of Saturn which was discovered by Richard Terrile in 1980 from Voyager photos and was designated S/1980 S 28.[5] 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.[6] 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.[7] In 2004 a faint, thin ring, temporarily designated R/2004 S 1, was discovered in the Atlantean orbit.[8]

High-resolution images taken in June 2005 by Cassini revealed Atlas to 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. The size of the equatorial ridge is comparable with the expected Roche lobe of the moon, which means that for any additional particles impacting the equator, the centrifugal force will nearly overcome Atlas's tiny gravity, and they will probably be lost.[7]

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. Because the orbits of Prometheus and Pandora are chaotic, it is suspected that Atlas's may be as well.[2]

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Notes

  1. Calculated from the standard gravitational parameter GM = (3.664±0.028)×10−4 km3·s–2 given by Lainey et al. (2023), divided by the gravitational constant G = 6.6743×10−2 km3·kg–1·s–2.[4]

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