Iapetus (moon)

Iapetus
	Iapetus as imaged by the Cassini orbiter in false color, September 2007. Iapetus's unusual coloration can be seen, with the equatorial ridge on the right limb. The large craters Engelier and Gerin are near the bottom.
Discovery
Discovered by	G. D. Cassini
Discovery date	October 25, 1671
Designations
Designation	Saturn VIII
Pronunciation	/aɪˈæpətəs/
Named after	Ἰαπετός Īapetus
Adjectives	Iapetian /aɪəˈpiːʃən/
Orbital characteristics
Semi-major axis	3560820 km
Eccentricity	0.0276812
Orbital period (sidereal)	79.3215 d
Average orbital speed	3.26 km/s
Inclination	17.28° (to the ecliptic); 15.47° (to Saturn's equator); 8.13° (to Laplace plane);
Satellite of	Saturn
Physical characteristics
Dimensions	1,492.0 × 1,492.0 × 1,424 km
Mean radius	734.4±2.8 km
Surface area	6700000 km2
Mass	1.80565×1021 kg
Mean density	1.0887±0.0127 g/cm3
Surface gravity	0.223 m/s2 (0.0228 g) (0.138 Moons)
Escape velocity	0.573 km/s
Synodic rotation period	79.3215 d ; (synchronous)
Axial tilt	zero
Albedo	0.05–0.5
Temperature	90–130 K
Apparent magnitude	10.2–11.9

Iapetus (/aɪˈæpətəs/) is the outermost of Saturn's large moons. With an estimated diameter of 1,469 km, it is the third-largest moon of Saturn and the eleventh-largest in the Solar System. Named after the Titan Iapetus, the moon was discovered in 1671 by Giovanni Domenico Cassini.

A relatively low-density body made up mostly of ice, Iapetus is home to several distinctive and unusual features, such as a striking difference in coloration between its leading hemisphere, which is dark, and its trailing hemisphere, which is bright, as well as a massive equatorial ridge running three-quarters of the way around the moon.

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