It's 'locked up' with amorphous minerals to the amount of two pints per cubic foot of dirt. Signs of life, on the other hand, remain elusive.

In the first series of the Curiosity rover’s analysis of fine Martian soil samples, scientists have found that two per cent of it is water by weight. They have also found other evidence that hint at liquid water having once existed on the planet.

The results were announced in a special edition of the journal Science on September 26, with five papers on the rover’s analyses, led by a review article from John P. Grotzinger, Project Scientist, NASA Mars Science Laboratory (MSL) mission.

Soil samples were picked up from a patch of sand, silt and dust called Rocknest. They were heated to 835 degrees Celsius and studied by instruments onboard the rover.

“The major gases released were water – about 2 per cent by weight of the sample – and carbon dioxide, oxygen and sulphur dioxide,” said Dr. Laurie Leshin of MSL, who was the lead author of the paper published by her team.

Analysis by the rover’s instruments found that, locked up in every cubic foot of Martian dirt, there were about two pints of water. “That’s a real resource for future explorers. We can access it with just a little bit of heating,” she quipped.

Her team also found carbonates, which are formed in the presence of water, and aluminosilicates, ferric compounds, and sulphates. Dr. Leshin notes that oxygen could have come from the breakdown of a perchlorate mineral. Perchlorates are a sensitive marker of past climate and could have participated in the transformation of Martian organic matter.

Because of similarities between the compounds in the soil and the atmosphere, the ‘dirt’ collected by the rover seems to have acted as a sponge for the atmosphere, which is where the volatile materials could be derived from.

“We can see that especially in the amount of the different types, or isotopes, of hydrogen. We know that the atmosphere contains extra heavy hydrogen, called deuterium. And we see that same thing in the water bound in the soil,” said Dr. Leshin.

The implication is that these minerals are constantly blown around by winds, and they mix with dust from other parts of the planet. This finding is supported by other papers in the special report, which found most of the minerals to be of basaltic origins.

“What we can say when we look at fine particles of sediment and dust like at Rocknest is that the minerals are largely basaltic and if fine grained minerals look like basalt there may be a global distribution of basaltic material mixed in with whatever is regional,” said Dr. Pamela Conrad, Deputy Principal Investigator, Sample Analysis at Mars instrument which heated the sample.

There was a notable exception. A lone, loose rock dubbed Jake_M, found on the plains along Curiosity’s path from its landing point, had a chemical composition unlike any other encountered on Mars. Scientists think it could have originated from a water-rich environment based on its similarities to rocks found in Earth’s rift zones.

Despite not moving too far away from the landing site, the dust collected by Curiosity is able to reveal a lot of geological information. That is because, unlike the landers and probes that came before it, Curiosity is equipped to investigate specific details like mineral structure and isotopic composition, essential to understand if Mars ever harboured life.

“By learning the nitty-gritty details of Martian dirt with Curiosity in one place on Mars, we are getting at global processes. What we’ve done is taken the next leap in our understanding of this dirt,” said Dr. Leshin.

The results in these five papers will be used to fine-tune future experiments on drilled rocks on the red planet, which are thought to better preserve signs of life that were absent in the Rocknest sample.

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