The Mars Curiosity rover has found evidence of water on the planet's surface

Curiosity finds water in Martian soil

The analytical suite of instruments in the belly of Nasa's Curiosity rover has found water in the Martian top soil.

The rover’s Sample Analysis at Mars (SAM) instrument suite enables the rover to identify a wide range of chemical compounds and determine the ratios of different isotopes of key elements using a gas chromatograph, a mass spectrometer and a tunable laser spectrometer

And analysis by SAM of a scoop of fine materials on the surface of the planet collected by the rover shortly after its August 2012 touchdown has shown that the soil contains about 2 per cent of water by weight, with results published today in journal Science.

"It was kind of a surprise to us," said Curiosity scientist Laurie Leshin from Rensselaer Polytechnic Institute in New York.

"If you take a cubic foot of that soil you can basically get two pints of water out it," she said. "The soil on the surface is really a little like a sponge for sucking stuff out of the atmosphere."

But more importantly for Paul Mahaffy, principal investigator for SAM at Nasa's Goddard Space Flight Center, the research confirms that the SAM suite is fulfilling its mission.

"This work not only demonstrates that SAM is working beautifully on Mars, but also shows how SAM fits into Curiosity's powerful and comprehensive suite of scientific instruments," he said.

"By combining analyses of water and other volatiles from SAM with mineralogical, chemical and geological data from Curiosity's other instruments, we have the most comprehensive information ever obtained on Martian surface fines. These data greatly advance our understanding surface processes and the action of water on Mars."

The SAM instrument suite takes up more than half the science payload on board the Mars Science Laboratory rover and features chemical equipment found in many scientific laboratories on Earth.

The Sample Analysis at Mars (SAM) instrument suite

The mass spectrometer is used to separate elements and compounds by mass for identification and measurement, while the gas chromatograph will heat soil and rock samples until they vaporize before separating the resulting gases into various components for analysis.

The laser spectrometer measures the abundance of various isotopes of carbon, hydrogen, and oxygen in atmospheric gases such as methane, water vapor, and carbon dioxide, accurate to within 10 parts per thousand.

For this study, scientists used the rover's scoop to collect dust, dirt and finely grained soil from a sandy patch known as Rocknest. Researchers fed portions of the fifth scoop into SAM where the dust, dirt and fine soil were heated to 835°C.

Scientists found that in addition to water, sulfur dioxide, carbon dioxide and other materials, the sands of Marsalso contain reactive chemicals known as perchlorates.

NASA's now-defunct Phoenix lander had found perchlorate in the planet's northern polar region, but scientists did not know until Curiosity's analysis that the chemical apparently is widespread.

"The isotopic ratios, including hydrogen-to-deuterium ratios and carbon isotopes, tend to support the idea that as the dust is moving around the planet, it's reacting with some of the gases from the atmosphere," Leshin said.

The results shed light on the composition of the planet's surface, while offering direction for future research.

"Mars has kind of a global layer, a layer of surface soil that has been mixed and distributed by frequent dust storms. So a scoop of this stuff is basically a microscopic Mars rock collection," said Leshin.

"If you mix many grains of it together, you probably have an accurate picture of typical Martian crust. By learning about it in any one place you're learning about the entire planet."

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