Dione

(dÿ-oh -nee) A satellite of Saturn, discovered in 1684 by Giovanni Domenico Cassini. It has a diameter of 1118 km and density of 1.4 g cm^–3, and is slightly larger than the satellite Tethys. An important characteristic of Dione is the nonuniformity of its brightness. The trailing hemisphere is dark, with an albedo of approximately 0.3, whereas the brightest features of the leading hemisphere have an albedo of approximately 0.6. Only Iapetus, of the Saturn system, displays a greater variation of brightness between the hemispheres. The surface shows evidence of a number of craters of 30–40 km, with a few large craters 165 km or more in diameter. There are some broad ridges in the southern part of the heavily cratered plains, with a long linear valley more than 500 km in length near the south pole. Dione's relatively high density compared with the neighboring satellites indicates a higher rock content of the interior. The most prominent feature is Amata, a crater 240 km in diameter associated with a system of bright wispy features that extend over the trailing hemisphere. The bright streaks on the surface first imaged by the two Voyager probes have been shown by the Cassini probe to be a vast system of linear features scarring the satellite's surface. A minor satellite, Helene, has been discovered to share the orbit of Dione. See also Table 2, backmatter.

Collins Dictionary of Astronomy © Market House Books Ltd, 2006

Dione

[′dī·ə‚nē]

(astronomy)

A satellite of Saturn that orbits at a mean distance of 2.35 × 10⁵ miles (3.78 × 10⁵ kilometers) and has a diameter of about 700 miles (1120 kilometers).