This image taken by NASA's Galileo spacecraft during its close flyby of Jupiter's moon Io on November 25, 1999 shows some of the curious mountains found there. The Sun is illuminating the scene from the left, and because it is setting, the Sun exaggerates the shadows cast by the mountains. By measuring the lengths of these shadows, Galileo scientists can estimate the height of the mountains. The mountain just left of the middle of the picture is 4 kilometers (13,000 feet) high and the small peak to the lower left is 1.6 kilometers (5,000 feet) high.