Crescent Callisto as seen from a distance of 410,000 kilometers by Voyager 1, with a resolution of 4 kilometers. The north pole is located about midway along the terminator (inside edge of crescent). Color images from a previous image sequence were used to produce this approximately "natural" color view.


Callisto is the outermost of Jupiter's four planet-sized moons and is dominated by impact craters. Despite this, a few more interesting features are also visible, including gigantic impact basins, suggestions of ancient volcanism, and a few ancient tectonic features. Among the most interesting features on Callisto are impact scars from tidally disrupted comets. Callisto is nearly as large as the planet Mercury. Its bulk density, however, is only ~1.8 grams per cubic centimeter, or only twice that of water ice. This indicates that the interior is approximately half water ice as well. Callisto is very similar in bulk properties to Ganymede, but apparently had a much simpler geologic history. The different geologic histories of these two bodies has been an important problem for planetary scientists, which may be related to the orbital and tidal evolution of Ganymede.

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This global view of Callisto was obtained by Voyager 1 in 1979. At this distance, Callisto is dominated by bright spots. At high resolution, these spots are revealed to be fresh, young impact craters and their ejecta patterns. Callisto is relatively brownish in color, possibly due to the contamination of the icy surface by meteoritic material.

Callisto & Ganymede Compared

Both Callisto and Ganymede are covered by huge tracts of relatively dark, heavily cratered terrains, shown here at similar image resolution and solar illumination. Ancient dark terrain on Ganymede is complex. Numerous parallel troughs (furrows) are probably part of a vast impact structure, similar to the rings observed at Valhalla (see below). Numerous scarps, smooth dark features, and thick crater-floor domes occur throughout dark terrain on Ganymede and indicate a complex geologic history. Ancient dark terrain on Callisto appears to have had a simpler geologic history. Scarps, furrows, and domes are rarely seen.

Valhalla Multiring Basin

This 4000-kilometer-wide impact structure consists of at least 25 concentric rings or ring arcs, and is one of the most unusual impact structures in the solar system. The unusual number of rings may be due to impact into a thin, icy lithosphere, which fractured very easily when the basin collapsed.


Gomul Catena

There are eight prominent crater chains on Callisto. They probably formed by the impact of comets that were tidally disrupted by the planet Jupiter, like the split comet Shoemaker-Levy 9 in 1992-1994. The observed number of chains suggests that comets are disrupted by Jupiter an average of once per 275 years or so. Gomul Catena is ~350 kilometers long, with craters up to 25 kilometers wide (scale bar is 100 kilometers long). The arcuate scarps are part of the vast Valhalla multiring impact basin.

Gipul Catena

This and other unusual crater chains on Callisto formed by the impact of tidally disrupted comets. This chain is ~620 kilometers long, with craters up to 40 kilometers across (scale bar is 100 km long). Gipul Catena is located near the north pole of Callisto. Several similar crater chains have also been identified on Ganymede.

Comet Shoemaker-Levy 9

This comet was shattered into ~21 fragments by tidal forces of Jupiter in July 1992. This Hubble Space Telescope image shows the comet in early 1994, prior to their plunge into Jupiter's atmosphere. The planet Earth has been added to show the scale of this string of comet fragments, although each individual fragment was probably no bigger than a kilometer or so. The bright areas surrounding each fragment are large halos of reflective dust. Compare this "string of pearls" with the prominent crater chains on Callisto. (Image courtesy of STScI and LPI.)

All images by Paul M. Schenk, Lunar and Planetary Institute, Houston, TX.

©Lunar and Planetary Institute, 1997

Supplemental Reading Materials

Beatty J. K., O'Leary B., and Chaikin A., eds. (1990) The New Solar System. Sky Publishing Corporation, Cambridge, Massachusetts; Cambridge University Press, New York. 326 pp.

Moons and Rings (1991) Voyage Through the Universe series. Time-Life Books, Alexandria, Virginia. 144 pp.

Rothery D. (1992) Satellites of the Outer Planets. Clarendon Press, Oxford. 208 pp.

McKinnon W. and Parmentier E. (1986) Ganymede and Callisto. In Satellites (J. Burns and M. Matthews, eds.), p. 437, University of Arizona Press, Tucson.

Morrison D., ed. (1982) Satellites of Jupiter. University of Arizona Press, Tucson. 972 pp.

Schenk P. (1995) The geology of Callisto. Journal of Geophysical Research, 100, 19023.

Schenk P. (1993) Central pit and dome craters: Exposing the interiors of Ganymede and Callisto. Journal of Geophysical Research, 98, 7475.

Schenk P. et al. (1996) Cometary nuclei and tidal disruption: The geologic record of crater chains on Callisto and Ganymede. Icarus, 121, 249-274.