December 16, 2004
The solar system's largest moon, Ganymede, is captured here alongside the
planet Jupiter in a color picture taken by NASA's Cassini spacecraft on
Dec. 3, 2000.
Ganymede is larger than the planets Mercury and Pluto and Saturn's largest
moon, Titan. Both Ganymede and Titan have greater surface area than the
entire Eurasian continent on our planet. Cassini was 26.5 million
kilometers (16.5 million miles) from Ganymede when this image was taken.
The smallest visible features are about 160 kilometers (about 100 miles)
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, Ganymede displays dark terrains that
NASA's 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 moons in the solar system. These are believed to be the
surface expressions of warm, pristine, water-rich materials that moved to
the surface and froze.
Ganymede has proven to be a fascinating world, the only moon known to have
a magnetosphere, or magnetic environment, produced by a convecting metal
core. The interaction of Ganymede's and Jupiter's magnetospheres may
produce dazzling variations in the auroral glows in Ganymede's tenuous
atmosphere of oxygen.
Cassini 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
mission for NASA's Office of Space Science, Washington, D.C.
Credit: NASA/JPL/University of Arizona
For higher resolution, click here.