Curiosity cradled by Gale Crater: this oblique view of Gale, and Mount Sharp in the center, is derived from a combination of elevation and imaging data from three Mars orbiters (NASA)
I was wrong to suggest the Curiosity rover (full name Mars Science Laboratory, MSL) will be looking for Martian life. MSL is a chemistry lab and will sniff for chemicals that could be relevant to life, but it won't be looking for biological organisms as such.
It's a robotic geologist too, and has landed at or near the end of an alluvial fan, a geological feature which forms when a stream of water flows on to a plain, slowing down and spreading out. Analysing this could answer one of the biggest questions about Mars: when did the planet lose most of its water?
Although NASA's Mars Exploration Programme has as its defining question "Life on Mars?", in the first few seconds of a recent video about Curiosity, project scientist John Grotzinger says, "Curiosity is not a life detection mission. We're not actually looking for life; we don't have the ability to detect life if it was there."
The video entitled The Science of Curiosity - Seeking Signs of Past Mars Habitability, is available on Stuart Clark’s Guardian astronomy blog. Unlike previous rovers sent to Mars, Curiosity is a robot chemist seeking evidence of past habitability on Mars, the video explains.
On the question of whether there is present-day life on Mars, there has been a subtle but important shift, it seems. MSL will confine its activities to looking for the ingredients of life on Mars and providing geological data on its climate history. I thought we had got past that stage, but not so. The prospects of finding present-day Martian life have dwindled in recent years, due to the absence of shallow underground lake systems, previously, but no longer, thought to exist.
Stuart Clark explains that NASA is playing an artful game to maximise scientific returns and secure future funding.
Gilbert Levin: I've already found it
In The Guardian on 3rd August Paul Davies traced the history of the search for life on Mars, beginning with the 1976 Viking mission. To this day the designer of the experiment, Gilbert Levin, insists he did find life on Mars, but he's out on a limb.
Davies says it's hard to know precisely what to look for. What would be an unambiguous signature of life anyway? Mars is very cold and very dry but of the two, the dryness is the more serious obstacle, water being crucial to known life. On Earth, the driest place is the Atacama desert in Chile. Astrobiologists speculate that it could host the closest analogue of what actual Martian might be like.