NASA announced nearly three-and-a-half years ago (on February 15, 2008), that for most of its life, Mars has been too briny to support life as we know it. Even the most hardy of Earth organisms would have had difficulty surviving for most of Mars’ history.
This deduction comes from analysis of a vast Martian plain that NASA has been examining for over 1,400 days. While I am perfectly willing to defer to men and women who are on the front line of this investigation, I still have to ask what we would conclude if we were to land a “rover” on the Utah salt flats. Even though this example is contrived, it makes a good point. Using “rovers” can unequivocally prove the existence of life on Mars simply by finding it, or by finding its undeniable footprint. Not finding anything, however, proves nothing.
The answer will come when visitors from Earth finally set foot on Mars and invest the necessary time to discover whether or not Mars ever had life. And the irony will be that in making this happen, we will have established life on Mars – and the Red Planet will never be the same.