A tantalising whiff of carbon-based compounds has been picked up by NASA's Curiosity Mars rover. But it's still not clear whether the eagerly awaited results show the true chemical nature of Mars or are the products of Earthly contaminants.
One of the main goals of the NASA rover is to search for signs of Martian habitability, including organics ? carbon-containing compounds that are the building blocks of life. The rover's first meals of baked Martian soil showed carbon and hydrogen reacting with chlorine inside the robot's ovens, creating organic molecules.
This taste of carbon is intriguing but it's a far cry from recent feverish speculation that the rover found definitive evidence for organics on the Red Planet. While the chlorine is almost certainly from Mars, it is still unclear whether the carbon is native Martian material or something from Earth that was trapped in the rover. Even if the carbon is from Mars, it may come from inorganic sources, like carbonate rocks.
"The rover has made this detection of simple organic compounds," said project scientist John Grotzinger of NASA's Jet Propulsion Laboratory in Pasadena, California. "We just don't know if they're indigenous to Mars or not."
Chemical diversity
The result is only one of the intriguing chemical discoveries the NASA rover has pulled from a wind-blown patch of sand at a site called Rocknest, unveiled today at the American Geophysical Union (AGU) 2012 fall meeting in San Francisco.
Since it landed in Gale Crater in August, Curiosity has been firing up its science tools one by one. Star of the show at the AGU meeting was the Sample Analysis at Mars (SAM) experiment, which can sniff the Martian atmosphere, and can analyse gases given off when soil samples are heated to as much as 1100 ?C.
SAM was the last major instrument to come online. Excitement surrounding the consistency of results emerging from multiple samples was what prompted Grotzinger to talk about data that's "for the history books" in a US radio interview almost two weeks ago, sparking a media frenzy.
"These results are an unprecedented look at the chemical diversity in the area," Michael Meyer, NASA's lead scientist for Mars exploration based in Washington, DC, said today at an AGU press briefing.
Earthly trace
SAM has been digesting scoops of fine sand, with grains less than 150 micrometres across. "It's finer than sugar, but coarser than something like flour," explains Ken Edgett, principal investigator for the rover's Mars Hand Lens Imager, which has taken detailed pictures of the material. It is this sand that revealed the chlorinated compounds.
SAM took several scoops from the Rocknest site in early October, shaking its tray and dumping out the first few loads to clean the instrument and make sure any Earthly molecules were flushed out of its system. The fifth scoop was delivered to SAM's oven, which heated it until the compounds inside released their characteristic gases.
The results revealed chlorinated carbon compounds, which probably formed inside SAM's oven rather than being picked up directly from Mars. The question is where the carbon comes from. Even after a thorough rinse, it's possible the SAM oven still contains traces of Earthly carbon.
If it's Martian in origin, the carbon may be from organic hydrocarbons or inorganic carbonates. The chlorine, meanwhile, may be from chemicals called perchlorates, which were previously spotted by NASA's Phoenix lander near the Martian north pole. These compounds are found in rocket fuel and other explosives and are typically considered toxic, but some extreme microbes on Earth may use them as an energy source.
?Hold the show'
The team will compare the result to tests of a sample of carbon-based material brought from Earth, Paul Mahaffy, SAM's principal investigator, said at the AGU meeting. "If we see the same stuff that we thought might be from Mars, we've got to say, ?Hold the show, this might be terrestrial stuff'."
Because the sand at Rocknest is representative of material blown from around the Martian surface, the new results provide a solid baseline describing the planet's global conditions. The data will later be compared to layers of rock at the rover's ultimate destination ? a 5-kilometre tall mountain known as Aeolis Mons, sometimes called Mount Sharp. Some of these layers formed more than 3 billion years ago, when it's thought that Mars was warm, wet and may have supported life.
Curiosity's sampling of the Martian soil has also revealed that the ratio of the heavy isotope deuterium to ordinary hydrogen is five times higher on Mars than on Earth ? a discovery that may help pinpoint when and how the Red Planet lost most of its formerly thick atmosphere.
Curiosity is now getting ready for its long trek to Aeolis Mons, taking in other points of interest on the way. Grotzinger likens Curiosity to a car with a 10,000-page user manual, which was still being written as the science team tested its instruments. With all the gear now up and running, it's time to drive, he says. "Our car is ready to go."
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