image: The Galilean satellite, Ganymede, which orbits Jupiter between Europa and outermost Callisto, is captured here alongside the planet in a true color narrow angle composite from December 3, 2000, 00:41 UTC (spacecraft time).
Ganymede is the largest satellite in the solar system, larger than the planet Mercury, and even larger than Saturn's largest satellite Titan. Both Ganymede and Titan have greater surface area than the entire Eurasian continent on our planet. The distance from the spacecraft to Ganymede is 26.5 million km. The smallest visible features are about 160 km across.
The bright area near the south (bottom) of Ganymede is Osiris, a large relatively new crater surrounded by bright icy material ejected by the impact which created it. Elsewhere on Ganymede, (for example, the area seen in the upper right) we see dark terrains that the Voyager and Galileo spacecraft have shown to be old and heavily cratered. The brighter terrains are younger and laced by grooves. Various kinds of grooved terrains have been seen on many icy satellites in the solar system. These are believed to the surface expressions of warm pristine water-rich materials that were once transported to the surface and froze.
Ganymede has proven to be a fascinating world, the only satellite known to have a magnetosphere produced by a convecting metal core. The interaction of the Ganymedian and Jovian magnetospheres may produce dazzling variations in the auroral glows in Ganymede's tenuous atmosphere of oxygen. The Cassini cameras will be used to search for these glows during the passage of Ganymede into Jupiter's shadow.
The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA's Office of Space Science, Washington, D.C. The imaging team consists of scientists from the US, England, France, and Germany. The imaging operations center and team lead (Dr. C. Porco) are based at the Space Science Institute in Boulder, Colo.
Credit: Cassini Imaging Team & NASA/JPL/University of Arizona