Curiosity Makes Big Water Discovery in Martian Dirt

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Future Mars explorers may be able to get all the water they need out of the red dirt beneath their boots, a new study suggests.

NASA’s Mars rover Curiosity has found that surface soil on the red planet contains 2 percent water by weight. That means astronaut pioneers could extract roughly 1 liter of water out of every 0.03 cubic meters of martian dirt they dig up, scientists said.

“For me, that was a big ‘wow’ moment,” said study lead author Laurie Leshin of Rensselaer Polytechnic Institute in Troy, N.Y. “I was really happy when we saw that there’s easily accessible water here in the dirt beneath your feet. And it’s probably true anywhere you go on Mars.”

The new study is one of five papers published in the journal Science Sept. 26 that report what researchers have learned about martian surface materials from the work Curiosity did during its first 100 days on the red planet.

Curiosity touched down inside Mars’ huge Gale Crater in August 2012, kicking off a planned two-year surface mission to determine if the planet could ever have supported microbial life. It achieved that goal in March, when it found that a spot near its landing site called Yellowknife Bay was indeed habitable billions of years ago.

But Curiosity did quite a bit of science work before getting to Yellowknife Bay. Leshin and her colleagues looked at the results of Curiosity’s first extensive Mars soil analyses, which the 1-ton rover performed on dirt that it scooped up at a sandy site called Rocknest in November 2012.

Using its Sample Analysis at Mars instrument, or SAM, Curiosity heated this dirt to 835 degrees Celsius and then identified the gases that boiled off. SAM saw significant amounts of carbon dioxide, oxygen and sulfur compounds — and lots of water on Mars.

SAM also determined that the soil water is rich in deuterium, a “heavy” isotope of hydrogen that contains one neutron and one proton (as opposed to “normal” hydrogen atoms, which have no neutrons). The water in Mars’ thin air sports a similar deuterium ratio, Leshin said.

“That tells us that the dirt is acting like a bit of a sponge and absorbing water from the atmosphere,” she said. 

SAM detected some organic compounds in the Rocknest sample as well — carbon-containing chemicals that are the building blocks of life here on Earth. But as mission scientists reported late last year, these are simple, chlorinated organics that likely have nothing to do with martian life. 

Instead, Leshin said, they were probably produced when organics that hitched a ride from Earth reacted with chlorine atoms released by a toxic chemical in the sample called perchlorate.

Perchlorate is known to exist in martian dirt; NASA’s Phoenix lander spotted it near the planet’s north pole in 2008. Curiosity has now found evidence of it near the equator, suggesting that the chemical is common across the planet. 

The presence of perchlorate is a challenge that architects of future manned Mars missions will have to overcome, Leshin said.

“Perchlorate is not good for people. We have to figure out, if humans are going to come into contact with the soil, how to deal with that,” she said.

“That’s the reason we send robotic explorers before we send humans — to try to really understand both the opportunities and the good stuff, and the challenges we need to work through,” Leshin added.