The map, published by the U.S. Geological Survey, technically illustrated the varied geologic character of Ganymede's surface, and is the first complete global geologic map of an icy, outer- planet moon, the researchers said.

A team of scientists, led by Wes Patterson of the Johns Hopkins Applied Physics Laboratory and Geoffrey Collins of Wheaton College, used images from U.S. space agency NASA's Voyager 1 and 2 spacecraft (1979) and Galileo orbiter (1995 to 2003) to create the map.

"By mapping all of Ganymede's surface, we can more accurately address scientific questions regarding the formation and evolution of this truly unique moon," Patterson said in a statement.

Since its discovery in January 1610, Ganymede has been the focus of repeated observation, first by Earth-based telescopes, and later by flyby missions and spacecraft orbiting Jupiter.

These studies depict a complex icy world whose surface is characterized by the striking contrast between its two major terrain types: the dark, very old, highly cratered regions; and the lighter, somewhat younger regions marked with an extensive array of grooves and ridges.

The researchers said the new map will be a valuable tool to compare the geologic characters of other icy moons, since almost any type of feature that is found on other icy satellites has a similar feature somewhere on Ganymede.

"The surface of Ganymede is more than half as large as all the land area on Earth, so there is a wide diversity of locations to choose from," Collins said. "Ganymede also shows features that are ancient alongside much more recently formed features, adding historical diversity in addition to geographic diversity."

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