by Timothy Oleson Monday, December 3, 2012
Too early to tell if findings are evidence of biological activity, scientists say
SAN FRANCISCO: The Curiosity rover has detected evidence of simple, chlorinated organic compounds in soil on Mars for the first time, project scientists announced Monday at the annual meeting of the American Geophysical Union in San Francisco. The scientists characterized the finding as very exciting, but they stressed that the results do not provide “definitive” evidence of past or present life on Mars.
“We really consider this a terrific milestone,” said Paul Mahaffy, principal investigator for the Sample Analysis at Mars (SAM) instrument suite that was used to analyze volatile components, including carbon-bearing molecules, water, oxygen and sulfur dioxide, in the soil. “It really is a rich data set” that has come out of the “first gulp of solid sample” for SAM, Mahaffy said. He added, however, that the results do not represent a “definitive detection of Martian organics.”
The chlorinated compounds identified were mostly simple hydrocarbons composed of just a single carbon atom bound to different numbers of chlorine atoms. Biological life creates complex organic compounds, which can then be broken down over time by radiation and other natural processes to simpler molecules similar to those found.
There are other explanations that must be ruled out first, though, before a link to life can be established. The simple hydrocarbons may have hitched a ride from Earth to Mars along with Curiosity. The chemical components — the carbon and the chlorine — might also have been delivered by asteroids or other interstellar objects that bombarded the planet in the past and that are known to carry carbon. Or, the compounds could have been created through non-biological chemical reactions involving carbon dioxide and perchlorate, a material that contains chlorine, both of which have previously been detected on Mars.
John Grotzinger, the mission’s project scientist echoed both Mahaffy’s excitement and caution: “SAM is working perfectly well. It has made this detection of organic compounds, simple organic compounds. We just simply don’t know if they’re indigenous to Mars,” Grotzinger said. Just the process of collecting a sample, depositing it into SAM and successfully analyzing it was a big achievement in its own right, he said.
The “garden variety” soil that was analyzed came from a rocky, sandy area dubbed “Rocknest” where the rover had been parked for several weeks. After scooping up several test samples to help clean it’s instrumentation and ensure a smooth delivery to SAM, Curiosity’s sampling arm picked up a fifth sample, sieved and sorted it, and then deposited it into the instrument. “We took something that we thought was a relatively average material and … we’ve learned a whole lot more about it than we knew before,” Grotzinger said.
Detecting complex molecules would have been even more interesting from the perspective of studying potential past life and habitable conditions, Mahaffy said. The first-of-their-kind results are a big step forward, however, especially given how early on in its mission Curiosity is. They also show that SAM is capable of detecting organics — one of the primary duties for which it is intended — and they provide valuable baseline data to compare with analyses of other rocks yet to come.
Following a nearly 570-million-kilometer trip through space and a remarkable landing sequence, NASA's Curiosity, also known as the Mars Sample Laboratory, touched down on the red planet in early August. Just four months into its planned two-year mission, the rover had already had a busy schedule and a long list of accomplishments before these latest findings. It had trekked hundreds of meters from its landing site, snapping numerous photographs of the landscape, the soil and itself along the way. It had also observed a large Martian dust storm and a transit of the planet’s moon, measured gas levels and radiation in the atmosphere, found that some basaltic rocks on Mars have similar compositions to those in Hawaii, and detected direct evidence of past flowing water.
An early indication that the Martian atmosphere might contain small amounts of methane, another possible sign of biological activity, was later found to be a false alarm, with mission scientists suggesting that small amounts of air from Earth that contained methane had made the trip with the rover and were likely responsible for the aberrant signal.
Today’s announcement comes two weeks after comments made by Grotzinger to NPR that early data from soil analyses performed by SAM was going to be “one for the history books” and that “it’s looking really good.” He then declined to give any further detail about what the data appeared to be showing. The tantalizingly vague remarks sparked waves of excited speculation that the rover had already detected potential signs of life on the red planet, the search for which is Curiosity’s primary mission.
Last week, NASA sought to quell the scientific gossip mill and temper expectations. In a statement released Thursday, the agency commented that “rumors and speculation that there are major new findings from the mission at this early stage are incorrect … At this point, the instruments on the rover have not detected any definitive evidence of Martian organics.”
Beyond addressing the nature and implications of the scientific findings, Grotzinger also responded today to questions about some of the perceived hype and build-up to today’s press conference.
“Certainly what I’ve learned from this is that you have to be careful about what you say and even more careful about how you say it,” he said. “We’re doing science at the speed of science … the enthusiasm that we had, that I had, that our whole team had about what’s going on here, I think was just misunderstood.”
Grotzinger said that watching the scientific developments of the Curiosity mission unfold requires “a healthy dose” of patience on the part of everyone involved, from scientists to the media and the public. Any major discoveries that do result, certainly including evidence of biological activity on the planet, are not going to come out of a single “hallelujah” moment, he said, but from careful studies over longer periods of time.
Currently at a site known as Point Lake, the rover will soon start on its way to an area called Yellowknife Bay before eventually heading to its ultimate destination at the base of Mt. Sharp, a mountain of layered sedimentary deposits situated in Gale Crater. The tentative near-term goal, which the team hopes to accomplish before the end of the year, Grotzinger said, is to find a suitable rock on which to test out Curiosity’s drill — the one tool that has not yet been used.
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