Channels in the solar system

Among the major discoveries made by planetary missions, channel structures, formed by a wide range of fluids such as water and lavas, have proven to be surprisingly common. Recent identification of gigantic flood channels in continental regions and submarine channels on the continental shelves provide new channel categories to an already rich inventory of terrestrial channels. Sinuous riles on the Moon, once hypothesized to have formed by water action, now constitute an important lava channel type. Mars has abundant evidence of an ancient warm-wet climate recorded in the channels, including an outflow channel which is the widest (∼200 km) known in the Solar System. Some lava channels observed on the flanks of the huge Martian shield volcanoes seem to have been modified by water. The Magellan radar mission revealed a wide range of volcanism on Venus. Most unusual is the great variety of channels produced by large-scale, low-viscosity lava eruptions. This includes potentially the longest channel in the Solar System (6800 km). Venusian atmospheric conditions alone do not produce sufficient differences in the lavas' cooling rates to explain the formation of many Venusian channels. The origin of these channels must be explained by eruption parameters, probable high discharge rates, high temperatures, long duration, and the possible involvement of very fluid silicates or lavas of exotic composition.