Ganymede moon surface has two main types of terrain. There are dark regions with numerous craters called impact craters and they cover one-third of the moon. The remainder of the moon is covered by lighter regions which have many ridges and grooves . The ridges are as high as 2000ft and stretch for thousands of miles.
The bumps on Ganymede surface are rock formations and if this is so, then dirt is also present. Ganymede is in fact made up of equal amounts of silicate rock and water ice.
Ganymede is believed to have a thick ocean between two layers of ice, one on the top and one on the bottom.
