An image of the Mars landscape taken by the Curiosity rover. Scientists… (NASA )
NASA's Curiosity rover has picked up intriguing signs of organic compounds in the Martian soil, but the key ingredient — carbon — may have been a castaway from Earth, scientists said Monday.
After completing an in-depth analysis of dust and sand from a Martian dune at a site called Rocknest, Curiosity's instruments have detected water, sulfur and chlorine compounds, said Paul Mahaffy, a member of the Mars Science Laboratory team based at Goddard Space Flight Center in Greenbelt, Md. Some of the rover's tests produced molecules that appeared to contain chlorine and carbon, but the scientists aren't yet sure what to make of the results.
The chlorinated methane and other molecules were detected by an instrument called Sample Analysis at Mars, which processes and heats soil samples. The measured chlorine levels were far too high to have originated from Earth, but the same can't be said of the carbon in the compounds, said John Grotzinger, lead scientist for the Mars Science Laboratory mission.
The results, presented at the fall meeting of the American Geophysical Union in San Francisco, capped nearly two weeks of feverish speculation that Curiosity might have detected clear signs of the precursors of life on the Red Planet.
Mahaffy, the lead investigator for the SAM instrument, put the kibosh on those hopes. "SAM has no definitive detection to report of organic compounds with this first set of experiments," he told a pack of reporters. (His more detailed recap of the first three months of the mission was so packed that security turned dozens of would-be attendees away.)
Scientists' hopes were raised several weeks ago, when Curiosity detected an initial signal of methane in atmospheric measurements. Most of the methane on Earth is produced by living things, and it's also thought to be a key precursor molecule for life.
But the finding turned out to be a false alarm — a double-check turned up no methane. That first signal was probably from a molecule that had hitched a ride from Florida and tainted the Martian sample. Such contamination is something the researchers have been wary of.
In any case, the carbon could still be inorganic if it's related to the carbon dioxide in the atmosphere, Mahaffy said. And SAM's oven could have cooked the carbon and the chlorine together to make some of the compounds the scientists think they're seeing in the sample.
It's hard to know for sure because some of the compounds aren't in crystalline form. That precludes scientists from using the other primary lab instrument in Curiosity's belly — a chemistry and mineralogy testing device called CheMin — to precisely identify compounds by bouncing X-rays off their mineral structure.
It will be a while before they can run another test to look for organic compounds, said Grotzinger, a Caltech geologist. That probably won't happen until after the team has tested the drill at the end of the rover's robotic arm. Even then, it will be a long while before scientists will be able to determine whether any carbon-based compounds are biological in nature.
First, he said, they'll have to see whether they find a similar signal in soils they sample down the road to Mt. Sharp, the 3-mile-high mound in the middle of Gale Crater whose layers could contain clues as to whether Mars was once hospitable to life.
"Curiosity's middle name is patience," Grotzinger said. "We all have to have a healthy dose of that."
Since touching down in Gale Crater on Aug. 5, Curiosity has zapped minerals with lasers, analyzed rocks with X-rays and digested sand in its sophisticated on-board laboratory.
In fact, the new results were almost secondary to the fact that the miniature lab-on-wheels actually worked, scientists said.
"We really consider this a terrific milestone, the two instruments buried deep inside Curiosity getting their first gulp of Mars material," Mahaffy said.
SAM also found a significant amount of deuterium, or heavy hydrogen, compared to the standard version of the element. This supports the idea that Mars once had a thicker atmosphere — crucial for liquid water and a warmer, more hospitable planet.