ARC-1989-AC89-7052

P-34718 Range: 210,000 kilometers (128,000 miles) This natural color image of the limb of Triton shows the largest surface features at about 3 miles across. The picture is a composite of images taken through the violet, green and clear filters and shows a geologic boundary between a rough, pitted surface to the right and a smoother surface to the left. The change between surface types is gradual. The image also shows a color boundary between pinkish material in the upper part of the image and whiter material in the lower part. The geologic and color boundaries are not the same. That implies that whatever supplies the color is a very thin coating over a different underlying material in which the geologic boundary occurs. The colored coating may be a seasonal frost composed of compounds volatile enough to be sublimated at the very low temperatures (40 K to 50 K or -387.4 F to -369.4 F) prevailing near Triton's surface. Possible compositions of the frost layer include methane (which turns red when irradiated), carbon monoxide or nitrogen. The color in this image is somewhat exaggerated: Triton is primarily a white object with a pinkish cast in some areas.