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Atlas (moon)
Encyclopedia
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 . 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
. 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 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
. In 2004 a faint, thin ring, temporarily designated , was discovered in the Atlantean orbit.
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 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.
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.
Inner satellite
In astronomy, an inner moon is a natural satellite following a prograde, low inclination orbit inwards of the large satellites of the parent planet. They are generally thought to have been formed in situ at the same time as the coalescence of the original planet...
of Saturn
Saturn
Saturn is the sixth planet from the Sun and the second largest planet in the Solar System, after Jupiter. Saturn is named after the Roman god Saturn, equated to the Greek Cronus , the Babylonian Ninurta and the Hindu Shani. Saturn's astronomical symbol represents the Roman god's sickle.Saturn,...
.
Atlas was discovered by Richard Terrile in 1980 (some time before November 12) from Voyager
Voyager program
The Voyager program is a U.S program that launched two unmanned space missions, scientific probes Voyager 1 and Voyager 2. They were launched in 1977 to take advantage of a favorable planetary alignment of the late 1970s...
photos and was designated . In 1983 it was officially named after Atlas
Atlas (mythology)
In Greek mythology, Atlas was the primordial Titan who supported the heavens. Although associated with various places, he became commonly identified with the Atlas Mountains in north-west Africa...
of Greek mythology
Greek mythology
Greek mythology is the body of myths and legends belonging to the ancient Greeks, concerning their gods and heroes, the nature of the world, and the origins and significance of their own cult and ritual practices. They were a part of religion in ancient Greece...
, because it "holds the rings on its shoulders" like the Titan
Titan (mythology)
In Greek mythology, the Titans were a race of powerful deities, descendants of Gaia and Uranus, that ruled during the legendary Golden Age....
Atlas held the sky up above the Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
. 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 for this ring. However, now it is known that the outer edge of the ring is instead maintained by a 7:6 orbital resonance
Orbital resonance
In celestial mechanics, an orbital resonance occurs when two orbiting bodies exert a regular, periodic gravitational influence on each other, usually due to their orbital periods being related by a ratio of two small integers. Orbital resonances greatly enhance the mutual gravitational influence of...
with the larger but more distant moons Janus
Janus (moon)
Janus is an inner satellite of Saturn. It is also known as Saturn X . It is named after the mythological Janus.-Discovery and orbit:Janus occupies practically the same orbit as the moon Epimetheus...
and Epimetheus
Epimetheus (moon)
Epimetheus is an inner satellite of Saturn. It is also known as Saturn XI. It is named after the mythological Epimetheus, brother of Prometheus.-Discovery:Epimetheus occupies essentially the same orbit as the moon Janus...
. In 2004 a faint, thin ring, temporarily designated , was discovered in the Atlantean orbit.
High-resolution images taken in June 2005 by Cassini reveal a saucer-shaped moon with a large smooth equatorial ridge
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 follow closely the moon's equator. They appear to be unique to the Saturnian system, but it is uncertain whether the occurrences are related or a...
. 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
Roche lobe
The Roche lobe is the region of space around a star in a binary system within which orbiting material is gravitationally bound to that star. If the star expands past its Roche lobe, then the material can escape the gravitational pull of the star. If the star is in a binary system then the material...
of the moon. This would mean that for any additional particles impacting the equator, the centrifugal force
Centrifugal force
Centrifugal force can generally be any force directed outward relative to some origin. More particularly, in classical mechanics, the centrifugal force is an outward force which arises when describing the motion of objects in a rotating reference frame...
will nearly overcome the tiny Atlantean gravity, and they will likely be lost.
Atlas is significantly perturbed by Prometheus
Prometheus (moon)
-Animations:-External links:* at ** anaglyph view of Prometheus...
and to a lesser degree by Pandora
Pandora (moon)
Pandora is an inner satellite of Saturn. It was discovered in 1980 from photos taken by the Voyager 1 probe, and was provisionally designated '. In late 1985 it was officially named after Pandora from Greek mythology. It is also designated as '.Pandora is the outer shepherd satellite of the F Ring...
, 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.