As mentioned earlier, we usually don't see surface changes
while they're taking place on other planets because
they occur over long periods of time. In a few cases,
though, we have been able to observe changes almost
as they're happening.
The image on the left is from the Viking lander on the surface of Mars. The image on the right show Jupiter's moon Io, as seen by the Voyager and Galileo spacecraft.
your cursor over each image to see another view of the
same place at a different time. Examine the before-and-after
images, and consider what might be responsible for the