Atlas is an inner satellite of

Saturn Saturn is the sixth planet from the Sun and the second-largest in the Solar System, after Jupiter. It is a gas giant with an average radius of about nine and a half times that of Earth. It has only one-eighth the average density of Earth; h ...

which was discovered by Richard Terrile in 1980 from

Voyager Voyager may refer to: Computing and communications * LG Voyager, a mobile phone model manufactured by LG Electronics * NCR Voyager, a computer platform produced by NCR Corporation * Voyager (computer worm), a computer worm affecting Oracle ...

photos and was designated . In 1983 it was officially named after

Atlas An atlas is a collection of maps; it is typically a bundle of maps of Earth or of a region of Earth. Atlases have traditionally been bound into book form, but today many atlases are in multimedia formats. In addition to presenting geogra ...

Greek mythology A major branch of classical mythology, Greek mythology is the body of myths originally told by the ancient Greeks, and a genre of Ancient Greek folklore. These stories concern the origin and nature of the world, the lives and activities o ...

, because it "holds the rings on its shoulders" like the

Titan Titan most often refers to: * Titan (moon), the largest moon of Saturn * Titans, a race of deities in Greek mythology Titan or Titans may also refer to: Arts and entertainment Fictional entities Fictional locations * Titan in fiction, fictiona ...

Atlas held the sky up above the

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's sur ...

. It is also designated . Atlas is the closest satellite to the sharp outer edge of the A ring, and was long thought to be a

shepherd satellite A ring system is a disc or ring, orbiting an astronomical object, that is composed of solid material such as dust and moonlets, and is a common component of satellite systems around giant planets. A ring system around a planet is also known as ...

for this ring. However, now it is known that the outer edge of the ring is instead maintained by a 7:6

orbital resonance In celestial mechanics, orbital resonance occurs when orbiting bodies exert regular, periodic gravitational influence on each other, usually because their orbital periods are related by a ratio of small integers. Most commonly, this relationsh ...

with the larger but more distant moons

Janus In ancient Roman religion and myth, Janus ( ; la, Ianvs ) is the god of beginnings, gates, transitions, time, duality, doorways, passages, frames, and endings. He is usually depicted as having two faces. The month of January is named for Jan ...

and Epimetheus. In 2004 a faint, thin ring, temporarily designated , was discovered in the Atlantean orbit. High-resolution images taken in June 2005 by '' Cassini'' revealed Atlas to have a roughly spherical centre surrounded by a large, smooth

equatorial ridge Equatorial ridges are a feature of at least three of Saturn's moons: the large moon Iapetus and the tiny moons Atlas and Pan. They are ridges that closely follow the moons' equators. They appear to be unique to the Saturnian system, but it is ...

. 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 In astronomy, the Roche lobe is the region around a star in a binary system within which orbiting material is gravitationally bound to that star. It is an approximately teardrop-shaped region bounded by a critical gravitational equipotential, ...

of the moon. This would mean that for any additional particles impacting the equator, the

centrifugal force In Newtonian mechanics, the centrifugal force is an inertial force (also called a "fictitious" or "pseudo" force) that appears to act on all objects when viewed in a rotating frame of reference. It is directed away from an axis which is paralle ...

will nearly overcome Atlas's tiny gravity, and they will probably be lost. Atlas is significantly perturbed by

Prometheus In Greek mythology, Prometheus (; , , possibly meaning " forethought")Smith"Prometheus". is a Titan god of fire. Prometheus is best known for defying the gods by stealing fire from them and giving it to humanity in the form of technology, kn ...

and to a lesser degree by

Pandora In Greek mythology, Pandora (Greek language, Greek: , derived from , ''pān'', i.e. "all" and , ''dōron'', i.e. "gift", thus "the all-endowed", "all-gifted" or "all-giving") was the first human woman created by Hephaestus on the instructions ...

, 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.

Gallery

File:Cassini Atlas N00084634 CL.png, Atlas from above its south pole (June 12, 2007) File:Atlas Rev09.2x.jpg, Atlas - ''Cassini''
(June 8, 2005). File:Atlas with rings.jpg, Atlas - A and F rings
(June 30, 2006). File:PIA17206-SaturnMoon-Atlas-Flyby-20151206.jpg, Atlas near the A ring
(December 6, 2015). File:F Ring and Atlas PIA10448.jpg, Atlas near the F ring
(May 9, 2005).

References

Citations Sources * * * * * *

External links

Atlas Profile
b
NASA's Solar System Exploration

NASA factsheet
{{DEFAULTSORT:Atlas (Moon) Moons of Saturn Astronomical objects discovered in 1980 Atlas (mythology) Moons with a prograde orbit