Ganymede

Voyager 1 took this picture of Jupiter's satellite Ganymede from a distance of 5 million miles (8.025 million kilometers) early on the morning of Feb. 26. Ganymede is the largest of Jupiter's 13 satellites. It is slightly larger than the planet Mercury, and has a density about twice that of water. That leads scientists to believe it is composed of a mixture of rock and ice. Ganymede is about four times brighter than Earth's Moon, and ground-based observations indicate a surface of water frost or ice. Details of the surface are not easily interpreted. The bright spot near the center of the picture is five times brighter than the Moon, and may contain more than surrounding areas. The bright pattern around the spot reminds scientists of ray craters on the Moon and Mercury, and the area may in fact be an impact crater that has exposed fresh, underlying ice. Further interpretation will require higher-resolution pictures. This color photo was taken through blue, green and orange filters and was assembled in the Image Processing Lab at Jet Propulsion Laboratory. JPL manages and controls the Voyager project for NASA's Office of Space Science.