Habitable Oasis on Mars?

The results from the Curiosity rover's first rock-drilling are in.

In the list of firsts for the NASA Curiosity rover’s mission, the last one on the list — the results from its first rock-drilling — are a major find: the revelation of what could be a former habitable environment on Mars.

Scientists announced today at a NASA press conference their analysis of bits of the rock John Klein, a sedimentary rock that Curiosity drilled into in February. By weight the rock is 20–30% smectite, a group of clay-like minerals that forms in the presence of water. The presence of calcium sulfates indicates the water probably had a relatively neutral pH, and the water also wasn't too salty. All told, the results suggest that this region of Gale Crater, called Yellowknife Bay, was once some sort of lake bed.

“We found a habitable environment that is so benign and supportive of life, that probably if this water was around and you had been on the planet, you would have been able to drink it,” said project scientist John Grotzinger (Caltech).

How large, deep, or long-lived this lake bed was, the scientists can’t say. They also can’t give a good estimate of when it existed, although the ballpark estimate is 3 billion years. That’s roughly around the time when life first arose on Earth, but take that with a grain of salt because the exact age at which Earth’s life appeared is debated.

What’s whetted scientists’ appetite (pun intended) is the hint of carbon and organic compounds. The carbon dioxide detected by the Sample Analysis at Mars (SAM) experiment could have been created from residual terrestrial carbon that contaminated the instruments — this is the first time the drill’s been used, so it’s too soon to say whether the compounds are natural to Mars, cautioned SAM principal investigator Paul Mahaffy (NASA Goddard). Two potential methane compounds also need confirmation.

Carbon would be exciting because microbes could use it in their metabolism. Other elements identified by SAM include oxygen, hydrogen, sulfur, and phosphorus. What’s also exciting is that the rock contains chemicals in both oxidized and non-oxidized forms — if you look at the rock post-drilling, the part revealed by the drill is gray, meaning it’s less oxidized that the reddish surface. This combination of oxidized and reduced chemicals could create an “energy gradient,” a chemical battery that could power primitive microorganisms.

None of these results means that microbes actually existed on Mars. But the Yellowknife Bay area is the first on Mars to show definite signs of past habitability.

The Curiosity team plans to drill again to confirm the results. But that will have to wait until May: technical problems required a rover reboot, delaying science operations, and solar conjunction is almost upon us, meaning Mars will be behind the Sun from our position and no communication with the rover will be possible.

The results don’t directly bear on the origin of Aeolis Mons, commonly called Mount Sharp. At the American Geophysical Union meeting last December, researchers using Mars Reconnaissance Orbiter images suggested that Mount Sharp might actually be a pile of dust scoured out by carefully directed winds, and not a sedimentary pileup as planetary scientists hoped. The jury’s still out on that, but as Curiosity finishes up at John Klein and heads for Mount Sharp it will continue taking samples to check how the rocks' compositions change on approach. It could be that Yellowknife Bay is part of Mount Sharp’s base, meaning the mound is indeed sedimentary, Grotzinger said — but only time will tell.