Dione (moon)
Dione (/daɪˈoʊni/), also designated Saturn IV, is the fourth-largest moon of Saturn. With a mean diameter of 1,123 km and a density of about 1.48 g/cm3, Dione is composed of an icy mantle and crust overlying a silicate rocky core, with rock and water ice roughly equal in mass. Its trailing hemisphere is marked by large cliffs and scarps called chasmata; the trailing hemisphere is also significantly darker compared to the leading hemisphere.
Dione photographed in natural light by the Cassini spacecraft in 2008 | |
| Discovery | |
|---|---|
| Discovered by | Giovanni Cassini |
| Discovery date | 30 March 1684 |
| Designations | |
Designation | Saturn IV |
| Pronunciation | /daɪˈoʊniː/ |
Named after | Διώνη Diōnē |
| Adjectives | Dionean /daɪəˈniːən/ |
| Orbital characteristics | |
Semi-major axis | 377396 km |
| Eccentricity | 0.0022 |
Orbital period (sidereal) | 2.736915 d |
| Inclination | 0.019° (to Saturn's equator) |
| Satellite of | Saturn |
| Physical characteristics | |
| Dimensions | 1128.8 × 1122.6 × 1119.2 km |
Mean radius | 561.4±0.4 km |
Surface area | 3964776.51 km2 |
| Mass | (1.0954868±0.0000246)×1021 kg (1.834×10−4 Earths) |
Mean density | 1.4781±0.0032 g/cm3 |
Surface gravity | 0.232 m/s2 |
| 0.51 km/s | |
Synodic rotation period | 2.736915 d (synchronous) |
| zero | |
| Albedo | 0.998±0.004 (geometric) |
| Temperature | 87 K (−186°C) |
| 10.4 | |
The moon was discovered by Italian astronomer Giovanni Domenico Cassini in 1684 and is named after the Titaness Dione in Greek mythology. Dione was first imaged up-close by the Voyager 1 space probe in 1980. Later, the Cassini spacecraft made multiple flybys of Dione throughout the 2000s and 2010s as part of its campaign to explore the Saturn system.