Io has a very tenuous atmosphere, composed in large part of sulfur dioxide. Its surface is a startling, vividly coloured landscape of erupting volcanic vents, pools and solidified flows of lava, and deposits of sulfur and sulfur compounds. There is no evidence of impact craters on this geologically young surface. Sulfur dioxide is the primary constituent of a thin atmosphere on Io. It has no water to speak of, unlike the other, colder Galilean moons. IO also has it's own magnetic field.