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| Click image for description | |
|---|---|
| Discovery | |
| Discovered by | Giovanni Domenico Cassini |
| Discovered in | 1671 |
| Orbital characteristics | |
| Semimajor axis | 3,561,300 km |
| Eccentricity | 0.0283 |
| Revolution period | 79d 7h 55m |
| Inclination | 7.52° |
| Is a satellite of | Saturn |
| Physical characteristics | |
| Mean diameter | 1436 km |
| Surface area | 6,700,000 km2 |
| Mass | 1.9739×1021 kg |
| Mean density | 1.27 g/cm3 |
| Surface gravityThis article covers the physics of gravitation. See also gravity (disambiguation). Gravitation is the tendency of masses to move toward each other. The first mathematical formulation of the theory of gravitation was made by Sir Isaac Newton and proved ast | 0.2553 m/s2In physics, acceleration (symbol: a is defined as the rate of change (or time derivative) of velocity. It is thus a vector quantity with dimension length/ time˛. In SI units, this is metre/second˛. To accelerate an object is to change its velocity over a |
| Rotation periodprograde planet like the Earth, the sidereal day is shorter than the solar day. At time 1, the sun and a certain distant star are both overhead. At time 2, the planet has rotated 360° and the distant star is overhead again (1→2 one sidereal day). | 79d 7h 55m ( synchronousIn astronomy, synchronous rotation is a planetological term describing a body orbiting another, where the orbiting body takes as long to rotate on its axis as it does to make one orbit; and therefore always keeps the same hemisphere pointed at the body it) |
| Axial tiltAxial tilt is an astronomical term regarding the inclination angle of a planet's rotation axis in relation to its orbital plane. It is also called obliquity . A planet whose rotation axis were perpendicular to the orbital plane would have an axial tilt of | 14.84° |
| AlbedoNote: This article discusses the physical or planetological property of albedo. For other usage, see Albedo (disambiguation). The albedo is a measure of reflectivity of a surface or body. It is the ratio of electromagnetic radiation reflected to the amoun | 0.04-0.5 |
| Atmosphere | none |
Iapetus ("eye AP uh tuss") is the third-largest moon of Saturn, discovered by Giovanni Domenico Cassini in 1671. It is named after the mythological Iapetus. It is also designated Saturn VIII.
Cassini named the four moons he discovered ( Tethys, Dione, Rhea and Iapetus) Lodicea Sidera ("the stars of Louis") to honour king Louis XIV. Astronomers fell into the habit of referring to them and Titan as Saturn 1 through Saturn 5. Once Mimas and Enceladus were discovered, in 1789, the numbering scheme was extended to Saturn 7.
The names of all seven satellites of Saturn then known come from John Herschel (son of William Herschel, discoverer of Mimas and Enceladus) in his 1847 publication Results of Astronomical Observations made at the Cape of Good Hope[1], wherein he suggested the names of the Titans, sisters and brothers of Cronos (the Greek Saturn), be used.