National Geographic : 1990 Aug
Scars of a torturedpastmark Triton. Ice volcanism is the favored theory for its young, brightsurface. "Lavas" of water ice, mixed perhaps with ammonia, likely flowed from caldera-like features (left). A computer generated perspective of that scene (below) looks down 200 meters (650 feet) into a basin 200 kilometers across. Proofof ongoing activity:A plume of nitrogen and dark parti cles (right)shoots eight kilome ters high before winds carry it 150 kilometers. Wearing bright halos, dark shapes as wide as 100 kilometers (below left) appear to be recent, though they lie on Triton's oldest terrain.