Dione

Dione , in astronomy, one of the named moons, or natural satellites, of Saturn . Also known as Saturn IV (or S4), Dione is 695 mi (1,120 km) in diameter, orbits Saturn at a mean distance of 234,500 mi (377,400 km), and has an orbital period of 2.737 earth days—the rotational period is unknown but is assumed to be the same as the orbital period. It was discovered in 1684 by the Italian-French astronomer Gian Domenico Cassini . Aside from Titan , Dione is the densest of Saturn's satellites; it is believed to be composed primarily of water ice with a considerable fraction of denser material, such as silicate rock. The trailing hemisphere is more heavily cratered than the leading hemisphere, which is the reverse of the cratering on most of the other Saturnian satellites. Another moon, Helene , is co-orbital with Dione; that is, it orbits Saturn at the same distance as Dione, and precedes Dione by about 60°. Dione also forms a satellite pair with Enceladus ; that is, the two moons interact gravitationally.

Dione (Saturn IV) One of the major satellites of Saturn, with a radius of 560 km; mass 10.52 × 10²⁰ kg; mean density 1440 kg/m³; visual albedo 0.7. It was discovered in 1684 by G. D. Cassini.

Dione The fourth-largest satellite of Saturn, 1120 km in diameter; also known as Saturn IV. Dione orbits 377 400 km from Saturn in 2.737 days, sharing its orbit with the much smaller Helene. Its axial rotation is the same as its orbital period. Dione was discovered in 1684 by G. D.Cassini. The two hemispheres of Dione show different crater densities, the trailing face being more heavily cratered. The trailing hemisphere also displays extensive bright complexes of scarps and fissures which give an overall appearance of wispy streaks many hundreds of kilometres in length. Dione's density is 1.5 g/cm³, suggesting that it consists of ice with a rocky core.