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None of these findings are dispositive, but their combined weight persuaded NASA scientists to summarize their findings in unusually explicit language. "We have concluded that the rocks here were soaked with liquid water," said Squyres flatly. "The ground would have been suitable for life."
Does that mean that there was--or still is--life on Mars? The fossil record on Earth suggests that given enough time and H2O, life will eventually emerge, but there's nothing in the current findings to prove that this happened on Mars. Without more knowledge of such variables as temperature, atmosphere and the length of time Martian water existed, we can't simply assume that what happened on our planet would necessarily occur on another.
Opportunity and its twin robot Spirit are not equipped to search for life. Their mission is limited to looking for signs of water. But there's still a lot for them to do. Just knowing that rocks were wet doesn't tell you if the water was flowing or stationary, if it melted down from ice caps or seeped up through the ground. And if water was once there in such abundance, where did it go? Opportunity, which is very likely to exceed its planned 90-day mission, is already looking for those answers, toddling off to investigate other rocks farther and farther from its landing site. Spirit is conducting its own studies in Gusev Crater, on the opposite side of the planet.
The next step--the search for life--will have to wait until 2013 or so. That's when NASA has tentatively scheduled the first round trip to Mars--a mission that will pluck selected rocks off the Red Planet and bring them back home for closer study. Whether humans will ever follow those machines--President Bush's January announcement notwithstanding--is impossible to say.