processes that shape planetary surfaces occur either very
slowly, requiring long periods of observation, or very
infrequently, meaning that you have to be looking at the
right time and place to see them happen at all.
we'd like to be able to observe planetary surfaces continuously
over long periods of time and in a reasonable amount of
detail. Assuming we could do it safely, it would also
be great to send scientists to study other planets, but
the cost would be truly astronomical! A more affordable
approach is to send robotic spacecraft to study the planets
and send data back to Earthbound scientists for analysis.