Scientists have discovered irregular lumps beneath the icy surface of Jupiter’s largest moon, Ganymede. These irregular masses may be rock formations, supported by Ganymede’s icy shell for billions of years.

This mosaic of Jupiter’s moon Ganymede consists of more than 100 images acquired with NASA’s Voyager and Galileo spacecrafts. The gravity anomalies or lumps inferred from the Galileo radio Doppler data are shown in red. The mosaic shows the surface of Ganymede with its geographic coordinate system and the Galileo gravity results superimposed.

The trajectory path of Galileo’s second Ganymede flyby on September 6, 1996, is shown in green. There are no obvious geologic features associated with the anomalies. For images and information about the Galileo mission, visit http://www.jpl.nasa.gov.