Atlas: Information from Answers.com

**Atlas**
Discovery
Photo taken by Cassini on June 12, 2007, showing Atlas as seen from above its south pole
Discovered by	Terrile, Voyager 1
Discovery date	October, 1980
Designations
Adjective	Atlantean
Orbital characteristics^[1]
Epoch December 31, 2003 (JD 2453005.5)
Mean orbit radius	137,670 ± 10 km
Eccentricity	0.0012
Orbital period	0.6016947883 d
Inclination	0.003 ± 0.004°
Satellite of	Saturn
Physical characteristics
Dimensions	46 × 38 × 19 km^[2]
Mean radius	15.3 ± 1.2 km ^[2]
Surface area	~3,700 km²
Volume	~15,000 km³
Mass	6.6 ± 0.6 × 10¹⁵ kg ^[1]
Mean density	0.44 ± 0.11 g/cm³
Equatorial surface gravity	~0.00083 m/s²
Escape velocity	~0.0062 km/s
Rotation period	synchronous
Axial tilt	zero
Albedo	0.4
Temperature	~81 K

Atlas (pronounced /ˈætləs/ AT-ləs, or as Greek Άτλας) 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 as 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 within Atlas's orbit.^[6]

High-resolution images taken in June 2005 by Cassini reveal a saucer-shaped moon with 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 size of Atlas's Roche lobe. This would mean that for any further particles attempting to accumulate on the equator, the centrifugal force overcomes Atlas's tiny gravity and they will 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]

Gallery

Atlas, as imaged by Cassini on June 8, 2005

With A and F rings to scale, Cassini

Near the F ring.

References

^ ^a ^b ^c Spitale, J. N.; et al. (2006). "The orbits of Saturn's small satellites derived from combined historic and Cassini imaging observations". The Astronomical Journal 132 (2): 692–710. doi:10.1086/505206. http://www.iop.org/EJ/article/1538-3881/132/2/692/205235.html.
^ ^a ^b Porco, C. C.; et al. (2006). "Physical Characteristics and Possible Accretionary Origins for Saturn's Small Satellites" (PDF). Bulletin of the American Astronomical Society 37: 768. http://www.lpi.usra.edu/meetings/lpsc2006/pdf/2289.pdf.
^ IAUC 3539: 1980 S 28 November 13, 1980 (discovery)
^ IAUC 3872: Satellites of Jupiter and Saturn September 30, 1983 (naming the moon)
^ ^a ^b E. Lakdawalla (June 13, 2007). "Funny little Atlas". The Planetary Society weblog. http://www.planetary.org/blog/article/00001003/.
^ IAUC 8401: S/2004 S 3, S/2004 S 4, and R/2004 S 1 September 9, 2004

External links

v • d • e Moons of Saturn

Generally listed in increasing distance from Saturn. Temporary names in italics.

Ring shepherds	Propeller moonlets (S/2009 S 1) · Pan · Daphnis · Atlas · Prometheus · ?S/2004 S 6 · ?S/2004 S 4 · ?S/2004 S 3 · Pandora

Co-orbitals	Epimetheus · Janus

Inner large (with Trojans)	Mimas · Enceladus · Tethys (Telesto • Calypso) · Dione (Helene • Polydeuces)

Inner small	Aegaeon · Methone · Anthe · Pallene

Outer large	Rhea (rings) · Titan · Hyperion · Iapetus

Inuit group	Kiviuq · Ijiraq · Paaliaq · Siarnaq · Tarqeq

Norse group	Phoebe · Skathi · S/2007 S 2 · Skoll · S/2004 S 13 · Greip · Hyrrokkin · Mundilfari · Jarnsaxa · S/2006 S 1 · S/2004 S 17 · Narvi · Bergelmir · Aegir · Suttungr · S/2004 S 12 · Bestla · Farbauti · Hati · S/2004 S 7 · Thrymr · S/2007 S 3 · S/2006 S 3 · Surtur · Kari · Fenrir · Ymir · Loge · Fornjot

Gallic group	Albiorix · Bebhionn · Erriapus · Tarvos

Rings of Saturn · Cassini-Huygens · Themis · Chiron

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