Iapetus (/aɪˈæpətəs/) is the outermost of Saturn's large moons. With an estimated diameter of 1,469 km (913 mi), it is the third-largest moon of Saturn and the eleventh-largest in the Solar System.[b] Named after the Titan Iapetus from Greek mythology, the moon was discovered in 1671 by Giovanni Domenico Cassini.
Iapetus
Iapetus in true color, as imaged by the Cassini orbiter in September 2007. Iapetus's unusual two-tone coloration can be seen, along with its massive equatorial ridge on the right limb.[a]
Discovery
Discovered by
G. D. Cassini
Discovery date
October 25, 1671
Designations
Designation
Saturn VIII
Pronunciation
/aɪˈæpətəs/[1]
Named after
Ἰαπετός Īapetus
Adjectives
Iapetian /aɪəˈpiːʃən/[2]: 248
Orbital characteristics[3]
Periapsis
3461972.4 km
Apoapsis
3661427.6 km
Semi-major axis
3561700 km
Eccentricity
0.028
Orbital period (sidereal)
79.331002 d
Average orbital speed
3.35 km/s
Inclination
7.6° (to Laplace plane)[3]
17.28° (to the ecliptic)
15.47° (to Saturn's equator)
Satellite of
Saturn
Physical characteristics
Dimensions
1493.4 × 1491.4 × 1424.2 km
(± 5.8 × 5.8 × 3.2 km)[4]
Mean radius
734.3±2.8 km[5][4]
Surface area
6777600 km2
Mass
(1.8056591±0.0000544)×1021 kg[3]
Mean density
1.0887±0.0127 g/cm3[3]
Surface gravity
0.223 m/s2 (0.0228 g) (0.138 Moons)
Escape velocity
0.573 km/s
Synodic rotation period
79.331002 d
(synchronous)
Axial tilt
8.298°[4]
Albedo
0.05–0.5[6]
Temperature
90–130 K
Apparent magnitude
10.2–11.9[7]
A relatively low-density body composed mostly of ice, Iapetus is home to several distinctive and unusual features, such as a striking difference in coloration between its dark leading hemisphere and its bright trailing hemisphere, as well as a massive equatorial ridge that runs three-quarters of the way around the moon.
Caption this Meme
