Clay equals water (Image: JPL-Caltech/NASA)

NASA’s Curiosity rover has found what it was looking for in its very first taste of Martian rock – much to everyone’s surprise. The scoop of grey powder contains definitive evidence that the Red Planet was once suited to life. All the signs are that Mars had plentiful, slightly salty water that could have supported primitive microbes.

The hope is that Mars can help us understand the origins of life – even if the planet’s early transformation into a cold, dry, hostile world meant life never got started there.

Determining the habitability of Mars was Curiosity’s chief goal when it landed in Gale crater in August 2012. But the rover was expected to hit pay dirt months from now, when it reached a 5-kilometre-high mound of layered sediments in the middle of the crater. Instead, it struck lucky with a sample of rock drilled on 9 February in an area called Yellowknife Bay, near what was probably an ancient streambed.


According to Curiosity’s on-board chemistry lab, the sample is between 20 and 30 per cent smectite, a clay mineral that forms in the presence of water. The instruments also detected minerals indicating that this water was pH neutral and carried substances capable of supplying microbes with energy.

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

At a scientific meeting in Texas this week, team members presented analyses from three of the rover’s remote sensing instruments that show many types of hydrated minerals, which form in the presence of water, scattered throughout Yellowknife Bay.

The thinking is that Mars would have had liquid water billions of years ago, around the time Earth was playing host to early life. But at some point Mars dried out and lost much of its atmosphere. The planet also only briefly had a magnetic field to protect its surface from cosmic radiation, which can damage DNA. These changes might have stopped any emergent life in its tracks or even prevented it from starting at all.

Records of the earliest life have been hard to find on warm, wet Earth. “Paradoxically, water, which is necessary for life, is a mild oxidant and can break down organic carbon,” says Grotzinger. But if microbes did exist on Mars, traces of them may still be preserved on the cold, dry world.

If we could find evidence primitive life got a start on Mars, that could fill in a lot of gaps in our understanding of conditions on early Earth, says Jeffrey Bada of the University of California in San Diego. “What we find on Mars won’t be a magic bullet to say, ‘Ah! That’s how we formed on Earth!’ But it would give us at least another example of what kind of chemistry we could try and mimic in the laboratory,” Bada says.

And even if no hints of microbes can be found, Mars’s habitable regions could still serve as snapshots of a prebiotic world frozen in time, says Michael Meyer, lead scientist for NASA’s Mars exploration programme. “Mars may have preserved that history of what was going on – what you might call proto-biology – before life even got started,” he says.

Mars may have preserved the history of what was going on before life even got started

NASA is now considering how best to equip the next rover, a Curiosity clone that will launch in 2020, says Meyer. Teams are expected to choose the science instruments by early 2014, based on recommendations from Mars researchers. “What we’re finding out now from Curiosity may affect what the review team wants to do, what instruments people propose, and what NASA ultimately selects,” says Meyer.

Mining mars for life-giving water As well as telling us more about past life, Martian water might be useful to future human visitors. Shifting heavy payloads from Earth to Mars is pricey, so colonising the Red Planet would be cheaper if we could mine the resources we need. That includes water, which is bountiful on Mars. But we couldn’t drink Martian water without first knowing what’s in it and how to make it safe, says Philip Metzger from NASA’s Kennedy Space Center. Now we know Gale crater once had water that was friendly to life (see main story), hinting that any underground ice might be too. “The news from Curiosity is hopeful, because the water might be easier to clean up, and therefore it might be easier to establish Mars outposts or colonies,” says Metzger. To collect Martian ice, mining robots may need to drill metres below the surface, which presents a few challenges. Friction from drilling can make the ice melt and refreeze, trapping the drill bit. And with Mars’s lower gravity, a machine would need a lot more counterweight to put pressure on a standard drill. Kris Zacny of Honeybee Robotics in California has a plan. Instead of adding counterweights, his drills vibrate like jackhammers to break up the ice. Sensors watch for drops in resistance that signal melting, so drills can stop automatically before becoming encased. Michael Slezak

This article appeared in print under the headline “Rover finds hint of life’s cradle on Mars”