Voyager 1 never got closer to Europa than 734 000 kilometers, and at that distance it remained a nearly featureless planet, with no obvious impact craters or other familiar geologic structures. What did show in the Voyager 1 pictures, however, were numerous thin, straight dark lines crisscrossing the surface, some extending up to 3000 kilometers in length. To the members of the Imaging Team, these features were “strongly suggestive of global-scale tectonic processes, induced either externally (as by tidal despinning) or internally (as by convection).” It was with the greatest interest that the Voyager 2 images, taken from about four times closer, were anticipated. The spectacular pictures obtained of the satellite in July were perhaps more confusing than clarifying. Europa is entirely covered with dark streaks that vary in width from several kilometers to approximately 70 kilometers and in length from several hundred to several thousand kilometers. Most streaks are straight, but others are curved or irregular. The streaks lie on otherwise smooth, bright terrain, featureless except for numerous random dark spots, most less than 10 kilometers in diameter. Voyager 2 photos showed, in addition to the smooth terrain with its dark streaks, regions of darker, mottled terrain. This mottled terrain appears rough on a small scale, and it may contain small craters just on the limit of resolution (about 4 kilometers). Only three definite impact craters have been identified, each about 20 kilometers across. This small number of craters suggests either that the surface is relatively young or that craters are not preserved for long in the icy crust. Although the dark streaks give Europa a cracked appearance, the streaks themselves are not obviously cracks. They are not depressed below their surroundings; in fact, they have no topographic structure whatever. Europa is extraordinarily smooth, and the dark streaks look rather like marks made with a felt-tipped pen on a white billiard ball. The streaks are not even very dark; the contrast with adjacent smooth terrain is only about 10 percent. One of the most remarkable geologic phenomena discovered by Voyager is the light streaks that appear on Europa. These are smaller than the dark streaks, only about 10 kilometers in width, but much more uniform. Seen at low Sun angle, they also show vertical relief of less than a few hundred meters. These light ridges are seen best at low Sun and tend to be invisible at higher illumination angles.