Why does one half of Dione have more craters than the other?
Start with the fact that
Saturn's moon Dione
always has one side that faces Saturn, and always has one side that faces away.
This is similar to
This tidal locking
means that one side of
Dione always leads as the moon progresses in its orbit,
while the other side always trails.
should therefore have undergone a significant amount of impacts on its leading half.
But the current leading half of
is less cratered than the trailing half!
A possible explanation is that some impacts were so large they spun
sometimes changing the part that suffered the highest impact rate before the
moon's spin again became locked.
it is the top part of Dione that appears significantly more cratered than the bottom half.