Planners of space exploration face an interesting trade-off. One on hand is financial reality: manned missions are much more expensive than unmanned missions, as the huge cost of the Apollo and Space Shuttle programs attests. One the other hand is the desire for knowledge: it is very difficult or even impossible to teach a machine to do the variety of tasks a human could do.

Since the end of the Apollo missions, and aggravated by a wane in public interest in space exploration, budgetary restrictions have limited planners of missions to other worlds in the solar system to unmanned craft. Since the last Apollo mission in 1983, advances in technology have allowed mankind to reach to point where we can vicariously explore the surface of another world -- even if only on a small scale so far.

In 1976, the Viking landers arrived on...