Iapetus

Iapetus , in astronomy, one of the named moons, or natural satellites, of Saturn . 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 Cassini . With a density of only 1.1, Iapetus is believed to consist almost completely of water ice. The reflectivity and surface features of its 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 trailing hemisphere is also heavily cratered, while the leading hemisphere is not. Unlike all the other moons but Phoebe , Iapetus's orbit is inclined to the plane of Saturn's equator.

Iapetus (Saturn VIII) One of the major satellites of Saturn, with a radius of 718km; mass 15.9 × 10²⁰kg; mean density 1020 kg/m³; visual albedo 0.05–0.5. It was discovered in 1671 by G. D. Cassini.

Iapetus The third-largest satellite of Saturn, diameter 1436 km; also known as Saturn VIII. It orbits 3 560 800 km from the planet's centre every 79.33 days, keeping the same face turned towards Saturn. Its leading hemisphere is far darker than the trailing hemisphere and polar regions, the albedos being about 0.05 and 0.5 respectively, so that its mean opposition magnitude varies between 10.2 and 11.9. The cause of this one‐sided darkening is not known. Impact craters cover its icy trailing face, the largest of which, called Roland, is 144 km in diameter, but few features have been seen on its dark leading hemisphere. Iapetus was discovered in 1671 by G. D.Cassini.