Explanation:
Why does one half of Dione have more craters than the other?
Start with the fact that
Saturn's moon Dione
has one side that always faces Saturn, and one side that always faces away.
This is similar to
Earth's Moon.
This tidal locking
means that one side of
Dione always leads as the moon progresses in its orbit,
while the other side always trails.
Dione
should therefore have undergone a significant number of impacts on its leading half.
Strangely, the current leading half of
Dione
is less cratered than the trailing half.
A leading explanation is that some crater-forming impacts were so large they spun
Dione,
changing the part that suffered the highest impact rate before the
moon's spin again became locked.
The above detailed image of Dione highlighting the moon's subtle hues
is a meticulously-constructed mosaic --
by an dedicated amateur --
of pictures taken during the April 2010
flyby of Dione by NASA's robotic
Cassini spacecraft.
