Opportunity might have found the Holy Grail of Mars exploration: clays bearing evidence of past, pH-neutral (and therefore life-friendly) water.

Spirit already found evidence of such past pH-neutral water, at Comanche Spur, near the volcanic formation Home Plate. (The only thing better than pH-neutral water, by the way, is pH-neutral water near a heat source -- like a volcano. That combination of life-friendly water and an energy source is exactly the kind of environment we think Earth life originated in.)

Opportunity has found numerous traces of water over the course of her mission, but it's all been acidic water, like the Rio Tinto here on Earth. We know life can survive in such an environment, but it's less likely it can start there. If Opportunity now finds evidence of pH-neutral water, that's tremendously exciting news: combined with the Spirit data, it means such water was once a global phenomenon.

It still doesn't answer the question of whether life ever originated on Mars; that's for later missions to decide. But it will mean, if proved, that life definitely once had a chance on the red planet.
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