NASA scientists have produced the first global geological map of Jupiter's largest moon Ganymede by combining images from over twenty years of observation by the Voyager spacecraft and the Galileo orbiter.

Ganymede, which as the largest moon in the Solar System is bigger than the planet Mercury, hosts a thick mantle of ice roughly 800km (497 mi) thick. The moon has two major terrain types, dark cratered areas and younger regions characterized by a plethora of grooves and ridges. The map, published by the US Geological Survey exhibits three distinct geological periods demarcated by cratering, tectonic disturbances and finally by a drop in geologic activity.

“This map illustrates the incredible variety of geological features on Ganymede and helps to make order from the apparent chaos of its complex surface,” says Robert Pappalardo of NASA's Jet Propulsion Laboratory.

A size comparison of Jupiter's four Galilean moons: Io, Europa, Callisto and Ganymede, which is pictured on the bottom right (Image: NASA)

With an equatorial circumference of 16,532 km (10,272 Mi) Ganymede presents an attractive target for global mapping as it hosts a surprising diversity of geographical characteristics. Future missions to map other moons will now be able to use Ganymede as a point of reference.

Further detailed observations of Jupiter's moons will be undertaken by the European Space Agency's Jupiter Icy Moons Explorer (JUICE) scheduled to arrive in orbit around Jupiter in 2030, whereupon it will spend at least three years taking measurements of the gas giant and its wards.

The animation below shows the geologic map of Ganymede superimposed over a global color mosaic. (Credit: USGS Astrogeology Science Ctr/Wheaton/ASU/NASA/JPL-Caltech)

Source: NASA