This image shows the grooved terrain of Ganymede.
Click on image for full size
The Grooved Terrain of Ganymede
This image shows an example of the grooved terrain of Ganymede.
The image clearly shows that some things hit Ganymede and made craters after the grooves were made, because the grooves are underneath the craters. This seems to indicate that the grooves were made almost 4 billion years ago, when the period of cratering was just about finished.
It was formerly thought that these grooves were a spreading feature similar to terrestrial seafloor spreading. A closeup view of these grooves, provided by the Galileo spacecraft, reveals a slightly different picture. The ridges are actually many ridges which have been pulled apart in a form of crustal extension. The spacing between each groove provides information about the underlying crust.
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