True, there will always be places where humans can't go due to the
extreme environment (i.e. on earth, unmanned submarines could arguably
dive deeper and explore tighter spaces than any manned vehicle). *But
Mars is especially attractive because it's conditions are quite suitable
for human exploration.

Jeff
--

Lets not forget a human will spend at least half his or her time on
mars not doing anything. But eating sleeping, bathing, cooking,
personal hygiene, exercising etc etc etc?.

And if ISS is any example most remaing time will be spent on maintence
of stuff.

What percent of ISS astronaut time is actually devoted to science?

Figure THAT into the man vs robot equasion.

Spirit and opportunities landing sites were selected for max landing
safety, not how interesting they are. although they have done great!

Follow ups should be produced, sent to more challenging locations,
send 20 assume 50% loss rate, that still leaves 10 more working on
mars