This week's Science magazine has 10 or 12 articles focused on the results from the Opportunity rover and analyses of the geology of the rocks near its landing site in Meridiani Plani. The articles are all behind a subscription wall, but a summary article by Jeffrey Kargel has linkouts to public sites. I will try to pull those in soon.
Two big points which struck me. First, Opportunity seems to be the whole show, in terms of evidence of a long-term presence of surface liquid water. The rocks at the Spirit site are volcanic in origin. *I have to change my blog wallpaper*
But the other is that even given the unique and strong evidence for liquid water at Meridiani Plani, Kargel at least is skeptical that organisms along the lines of earth extremophiles could hack out a life there. That is, there are Earth microbes which tolerate very high salt, those which tolerate cold, and those which tolerate strongly acidic environments-- but very few Earth organisms can tolerate all three. So even when Meridiani Plani was warmer and wetter, it woud still have been off the charts in terms of earth habitats.
I had always thought that the landing sites were chosen with the aim of proving liquid water. Nothing would be more definitive than a salt flat, so I had just assumed that the saltiness of the Opportunity rocks was part of the plan. But it seems the site had also been chosen with life habitats explicitly in mind. Thus, this week's results appear to be a true negative, rather than the absence of a positive.