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Already intriguing patterns of unknown origin appear on the surface of Neptune's largest satellite, Triton, in this image returned by Voyager 2.
The image was taken Aug. 22, 1989, from a distance of 4 million km (2.5 million miles). Voyager images show that Triton's diameter is about 2,720 kn (1,690 miles), and that it is one of the brightest objects in the solar system, reflecting about 70 percent of the sunlight that strikes it. This is the hemisphere of Triton that always faces away from Neptune.
The south pole is near the bottom of the image. Triton's rotation axis is tilted so that the latitude at the center of the disk is 55 degrees south. Dark regions at the top of the disk extend from roughly the equator to beyond 20 degrees north. The margin between the bright and dark regions varies with longitude around the satellite. The gray, featureless area just to the right of the center of the disk is due to a reseau (reticule mark) in the camera. Voyager 2 will make its closest approach to Triton on Aug. 25, when it will pass within 40,000 km (25,000 miles) of the satellite.
The Voyager Project is managed for NASA by the Jet Propulsion Laboratory, Pasadena, Calif.