Iapetus


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Iapetus,

in Greek mythology, a Titan. By the nymph Clymene he fathered Atlas, Prometheus, Epimetheus, and Menoetius.

Iapetus

(īăp`ĭtəs), in astronomy, one of the named moons, or natural satellites, of SaturnSaturn,
in astronomy, 6th planet from the sun. Astronomical and Physical Characteristics of Saturn

Saturn's orbit lies between those of Jupiter and Uranus; its mean distance from the sun is c.886 million mi (1.
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. Also known as Saturn VIII (or S8), Iapetus is 907 mi (1460 km) in diameter, orbits Saturn at a mean distance of 2,212,885 mi (3,561,300 km), and has equal orbital and rotational periods of 79.33 earth days. Saturn's third largest moon, it was discovered in 1671 by the Italian-French astronomer Gian Domenico CassiniCassini
, name of a family of Italian-French astronomers, four generations of whom were directors of the Paris Observatory. Gian Domenico Cassini, 1625–1712, was born in Italy and distinguished himself while at Bologna by his studies of the sun and planets,
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. With a density of only 1.1, Iapetus is believed to consist almost completely of water ice. A notable surface feature is a ridge that encircles it along its equator and rises as high as 12 mi (20 km). The reflectivity and surface features of Iapetus's leading and trailing hemispheres are noticeably different. The leading hemisphere is remarkably dark, while the trailing hemisphere is light—the asymmetry is so marked that Cassini wrote that he could see Iapetus on one side of Saturn but not on the other. The difference in reflectivity is due in part to the accumulation of dust on the leading hemisphere; this dust is believed to come from the enormous but faint ring of Saturn discovered in 2009. Much of the difference in reflectivity, however, is believed to be due to residue left behind by the sublimation of ice. The trailing hemisphere is also heavily cratered, while the leading hemisphere is not. Unlike all the other moons but PhoebePhoebe
, in astronomy, one of the named moons, or natural satellites, of Saturn. Also known as Saturn IX (or S9), Phoebe is 137 mi (220 km) in diameter, orbits Saturn at a mean distance of 8,047,985 mi (12,952,000 km), has an orbital period of 550.
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, Iapetus's orbit is inclined to the plane of Saturn's equator.

Iapetus

(ÿ-ap -ĕ-tŭs) A satellite of Saturn, discovered in 1671 by Giovanni Domenico Cassini. The diameter of Iapetus is 1440 km so that in size it is the twin of the satellite Rhea but its density, 1.21 g cm–3, is much lower. It is a strange satellite with a dark leading hemisphere (albedo 0.04–0.05) compared with a bright trailing edge of albedo 0.6. The dark hemisphere carries the name Cassini Regio. It appears to be coated with some dark material. The demarcation between the dark and light regions is not abrupt and there is a transition region 200–300 km in width with a meandering boundary. The bright trailing edge is most heavily cratered; some of the craters have dark floors but it is not known if the dark material in them is the same as that covering Cassini Regio. The material on the leading edge is thought to be carbon-based, but it is unclear whether it was emitted from the interior of Iapetus or was debris from eruptions on other Saturnian satellites swept up by Iapetus from space.

Iapetus was photographed by Voyager 2 in 1981 and by Cassini–Huygens in 2004. The Cassini images revealed some new features not seen on the Voyager images, in particular a vast ancient impact basin over 400 km across, which has been heavily overprinted with more recent smaller craters, and a curious and extraordinary ridge that almost exactly coincides with Iapetus' equator. It appears as a 20-km-wide band, 1300 km long, that seems to girdle the whole satellite, extending above the surface of Iapetus to a height of up to 13 km. The equatorial ridge may be a mountain belt that has folded upward, or perhaps it was formed when material from inside Iapetus erupted onto the surface through a crack and accumulated locally.

See also Table 2, backmatter.

Iapetus

 

a satellite of Saturn, approximately 1,800 km in diameter and located at a mean distance of 3,563,000 km from the center of Saturn. It was discovered in 1671 by G. D. Cassini.

Iapetus

[‚yap·əd·əs]
(astronomy)
A satellite of Saturn that orbits at a mean distance of 2.207 × 106 miles (3.560×106 kilometers) and has a diameter of about 900 miles (1500 kilometers).
References in periodicals archive ?
Using pictures taken by Cassini, particularly during a September 2007 close fly-by, the scientists assert that Iapetus' darker half, called Cassini Regio, is the result of the planet's leading side getting bombarded by dusty debris from another Saturnian moon, Phoebe, which orbits in the opposite direction beyond Iapetus.
555 Ga Marystown events [#21b] are recorded in the Avalon zone, which had an uncertain relationship with Laurentia during this period and subsequently drifted with Gondwana before closure of the Iapetus Ocean in the early Paleozoic.
The close-up images of Iapetus during the [Cassini] mission orbit will be spectacular," predicts Jonathan I.
1b) parallel the Iapetus Suture and mark significant kilometric-scale sinistral displacements of crustal blocks during the end stages of the orogen (Dewey and Strachan 2003).
Paleomagnetic and fossil data suggest they can be separated into peri-Laurentian (Notre Dame Subzone) and peri-Gondwanan (Exploits Subzone) terranes, which formed on opposite sides of Iapetus and are separated by the Red Indian Line.
The oldest rocks in the Napadogan area are deep-water, turbiditic, interbedded slate and quartzite of the Miramichi Group, deposited during the Cambrian and Tremadoc on the continental slope along the northwest side of the Gander margin bordering the Iapetus ocean (Rice and van Staal 1992; van Staal et al.
The continents drifted towards each other and the Iapetus Ocean disappeared as the land masses collided.
This rifting created the Iapetus Ocean, a predecessor of the Atlantic.
It's unlikely that the proto-Saturn nebula was big enough to form the massive moons Titan and Iapetus as far away as they are now from the planet, or that the mid-size moons near the rings could have ended up with such a wide range of densities (Tethys must be nearly pure ice, whereas neighboring Enceladus and Dione contain lots of rock).
Similar conditions dominated in the Laurentia palaeocontinent, on the other side of the Iapetus ocean, where the algal flora of the Medusaegraptus epibole and similar Konservat-Lagerstatten of North America were described (LoDuca & Brett 1997).