A medium-sized satellite of Saturn, discovered by G. D. Cassini in 1684. Images from the Voyager 1 mission show several different types of terrain on Dione: heavily cratered areas, cratered plains with a lower density of craters, and smooth plains with few craters or other features. The largest craters are over 200 kilometres 125 miles across, and craters over 100 kilometres are common in the heavily cratered areas. Another noticeable feature is an irregular network of light wispy streaks on a dark background, which, it has been suggested, may be frosty deposits.