False-colour Voyager 2 image of Neptune's largest moon, Triton, showing its pinkish, pitted, icy surface. The image shows a geological boundary between two different types of terrain: the smooth, dark surface at bottom and the patchy, pitted terrain at top. The dark terrain is crossed by long, narrow canyons and may be volcanic in origin. The pinkish colouration is thought to be due to a thin coating of methane frost. The elongated dark streaks seen in this image probably represent particulate materials blown in the same direction by the prevailing wind. The streaks appear to originate from very small circular sources, which may be small volcanic vents.