The sequestration of ethane on Titan in smog particles

Need smust on Titan Prior to the visit of the Cassini-Huygens probe there, planetary scientists expected to find a giant ocean of liquid ethane on Saturn's moon Titan. Exposure to solar ultraviolet light over the life of the Solar System should have produced enough ethane, from methane dissociation, to form a satellite-wide ocean a kilometre deep. But no ocean was found, just a cloud of ethane above the southern pole and a few lakes. Donald Hunten explains the dearth of liquid ethane by its condensation on the abundant smog particles, rather than into liquid drops at low temperatures. This dusty combination of smog and ethane — or 'smust' — may form deposits several kilometres thick on Titan's surface. The mysterious absence or rarity of liquid ethane on Titan is explained by its condensation onto the smog particles in the atmosphere at the cold temperatures. This dusty combination of smog and ethane forms deposits several kilometres thick on the surface, named 'smust'. Saturn's largest satellite, Titan, has a dense atmosphere of nitrogen with a few per cent of methane 1 . At visible wavelengths its surface is hidden by dense orange-brown smog, which is produced in the stratosphere by photochemical reactions following the dissociation of methane by solar ultraviolet light. The most abundant of the products of these reactions is ethane, and enough of it should have been generated over the life of the Solar System to form a satellite-wide ocean one kilometre deep 2 . Radar observations 3 have found specular reflections in 75 per cent of the surface spots observed, but optical searches for a sun-glint off an ocean have been negative 4 . Here I explain the mysterious absence or rarity of liquid ethane: it condenses onto the smog particles, instead of into liquid drops, at the cold temperatures in Titan's atmosphere. This dusty combination of smog and ethane, forming deposits several kilometres thick on the surface, including the observed dunes and dark areas, could be named ‘smust’. This satellite-wide deposit replaces the ocean long thought to be an important feature of Titan.