It’s a rather historic moment in the annals of space exploration and the search for life beyond Earth. The Curiosity rover touched down on Mars last year and has ever since been slowly wending its way across a massive crater that NASA has shown was once covered in water. And now it is about to aim Curiosity’s rock drill at vein targets on the surface of Mars. It marks the first extra-terrestrial drill program.
From a purely technical standpoint, the mission is already an amazing feat. Fly a compact car-sized rover to a neigbouring planet; drive across part of the Gale crater that has a mountain taller than Mount Rainier (~4,400 metres) in its centre; and test everything possible using a laser beam, digital cameras, a scoop, a drill and a suite of analytical tools that help to describe samples. And all on a mission in a crater climate where the temperature varies from minus 70 degrees centigrade to a little bit over the freezing point (a balmy seven degrees was detected one afternoon).
But it’s the search for life – Curiosity’s raison d’être – that matters most to the public and that is about to begin in earnest with the coming drill program. Targets have been chosen. Drills will likely turn within two weeks, NASA said this week.
The rocks in NASA’s sights have are already proven intriguing, especially for what they say about water on Mars, its past climate and the Red Planet’s geology at the drill site proper, called “John Klein”, after a NASA scientist who passed away recently. Among the first targets NASA is aiming the Curiosity drill are veins rich in calcium sulfate – possibly similar to gypsum on Earth – that would have most likely formed in a wet environment. The calcium sulfate on Mars, shown below to the left, would have filled fractures in sediments as water circulated through them. They look quite a lot like gypsum veins in the Sahara desert, pictured on the right.
The stuff of major headlines would be what NASA’s drill program might say about the possibility life existed on Mars, in particular whether there are molecules containing organic carbon on the Red Planet. As NASA puts it in press material, while these molecules can exist without life, “life as we know it cannot exist without them, so their presence would be an important plus for habitability.” But NASA isn’t advertising such a grand discovery from Curiosity’s first drilling program, though it is conceivable this evidence could be found.
At this point the mission and humankind’s first extra-terrestrial drill program is best thought of as the most high-tech, in depth geological mapping program of a small portion of Mars that was covered in water, ever conceived. In a conference call yesterday (audio link here) in which the Curiosity team went over results found so far, the emphasis was not on finding a smoking gun in the detection of life on Mars, but on the diversity of sedimentary units, almost undoubtedly deposited in watery environments, that NASA has encountered so far both on its drive to the drill site and at the site itself.
In the call John Grotzinger, chief scientist on the Curiosity team, was especially excited about the coming drill program into the calcium sulfate veins, identified at the chemical level with Curiosity’s pulsing laser beam called the ChemCam. One of the main points Grotzinger emphasized was that in Mars’ past the area had obviously been wet. In his own words he said, “What these vein fills tell us is that…water moved, it percolated through these rocks, through these fracture networks, and then minerals precipitated to form the white material which ChemCam says is very likely a calcium sulfate probably hydrated in origin.”
Now the drill campaign into the Mars veins will give NASA a much closer look at the rocks in this once water-logged zone. It will get at the mineral make-up of the calcium sulphate veins. It will assess what appears to be multiple phases of water cover. It will expand on the chemical composition of the samples, including their isotope ratios which can speak to past climate conditions, among other things.
The results from these tests will be interesting enough for geologists and Marsophiles.
But it was the final test on the drill samples Grotzinger mentioned and the possible implications of this analysis that has the greatest chance of capturing the public’s imagination. Grotzinger said they would “look for organics as well” in the calcium sulfate veins.
In this final pursuit, one scientist who follows progress on the project, cautioned against hype. William Schopf, a paleobiologist at the University of California and the director of the Center for the Study of Evolution and the Origin of Life (CSEOL), agreed that gypsum on Mars was a “very promising material to look at” but that in Curiosity’s case “We should be really really cautious about what can be learned robotically from Mars.”
He noted, for instance, that Curiosity does not have powerful enough optics to see microscopic fossilized life that might be preserved in gypsum, as it is in some but not all cases on Earth. Such an endeavour would likely require getting samples from Mars back to Earth. That said, Schopf did hold out some hope for what gypsum might tells us about life or living conditions on Mars if the gypsum originated from dried up remnants of oceans or lakes. Then Curiosity might be able to detect carbonaceous material, maybe originating from living organisms, if it was abundant enough.
“That will be a huge big smoking gun,” Schopf said.
But, smoking gun’s aside, he returned to his more pragmatic stance on the pace and prospects for major discoveries on NASA’s Curiosity mission. “Remember not to get too excited,” Schopf said. Then he concluded our interview with one of Carl Sagan’s better known quotes. “This impatience with ambiguity can be criticized in the phrase: absence of evidence is not evidence of absence.”