Did liquid water once flow on this dry and dusty world? Did it support life in any form? And are there remnants left to find? The science that comes out of the Mars missions may help answer a much larger, more philosophical question.
Is our planet Earth the norm, in a galaxy run through with life-bearing planets? Or is Earth a rare gem, with a unique make-up and history that allowed it to give rise to living things? On Mars, Curiosity has spotted pebbles and other rocks commonly associated with flowing water.