Atlas (moon)

Infobox Planet
name = Atlas


caption = Photo from Cassini taken 12 June 2007, showing Atlas as seen from above its south pole
bgcolour = #a0ffa0
discovery = yes
discoverer = Terrile, Voyager 1
discovered = October, 1980
orbit_ref =cite journal | author= Spitale, J. N.; "et al."| title= "The orbits of Saturn's small satellites derived from combined historic and "Cassini" imaging observations"| journal= The Astronomical Journal| year= 2006| volume= 132| issue=2 | pages= 692–710 | url=http://www.iop.org/EJ/article/1538-3881/132/2/692/205235.html | doi= 10.1086/505206]
epoch = 31 December 2003 (JD 2453005.5)
mean_orbit_radius = 137,670 ± 10 km
eccentricity = 0.0012
period = 0.6016947883 d
inclination = 0.003 ± 0.004°
satellite_of = Saturn
physical_characteristics = yes
dimensions = 46 × 38 × 19 kmcite journal | author= Porco, C. C.; "et al."| title= "Physical Characteristics and Possible Accretionary Origins for Saturn's Small Satellites"| journal= Bulletin of the American Astronomical Society| year= 2006| volume= 37| pages= 768| url=http://www.lpi.usra.edu/meetings/lpsc2006/pdf/2289.pdf]
mean_radius = 15.3 ± 1.2 km
surface_area = ~3,700 km²
volume = ~15,000 km³
mass = 6.6 ± 0.6 e|15 kg
density = 0.44 ± 0.11 g/cm³
surface_grav = ~0.00083 m/s²
escape_velocity = ~0.0062 km/s
rotation = synchronous
axial_tilt = zero
albedo = 0.4
single_temperature = ~81 K
adjectives = Atlantean

Atlas (pronEng|ˈætləs respell|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 nowrap|S/1980 S 28. [ [http://cfa-www.harvard.edu/iauc/03500/03539.html IAUC 3539: "1980 S 28"] 1980 November 13 (discovery)] 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. [ [http://cfa-www.harvard.edu/iauc/03800/03872.html IAUC 3872: "Satellites of Jupiter and Saturn"] 1983 September 30 (naming the moon)] It is also designated as nowrap|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. cite web
url=http://www.planetary.org/blog/article/00001003/
title="Funny little Atlas"
author=E. Lakdawalla
date=13 June, 2007
work=The Planetary Society weblog] In 2004 a faint, thin ring, temporarily designated nowrap|R/2004 S 1, was discovered within Atlas's orbit. [ [http://cfa-www.harvard.edu/iauc/08400/08401.html IAUC 8401: "S/2004 S 3, S/2004 S 4, and R/2004 S 1"] 2004 September 9]

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' tiny gravity and they will be lost.

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.

Gallery

References

External links

* [http://solarsystem.nasa.gov/planets/profile.cfm?Object=Sat_Atlas Atlas Profile] by [http://solarsystem.nasa.gov NASA's Solar System Exploration]
* [http://www.planetary.org/explore/topics/saturn/atlas.html The Planetary Society: Atlas]
* [http://sse.jpl.nasa.gov/planets/profile.cfm?Object=Sat_Atlas&Display=Facts NASA factsheet]