Despite widespread speculation about a potentially significant discovery on Mars, the Curiosity rover's first detailed look at a martian soil sample with an instrument capable of detecting organic compounds has not found any "definitive" signs of materials that play key roles in biological processes on Earth, scientists said Monday.
While the rover's Sample Analysis at Mars, or SAM, instrument detected signs of an oxygen-chlorine compound -- perchlorate -- and trace amounts of chlorinated methane compounds, which contain carbon, researchers say more tests are needed to make sure the carbon originated with the sample and was not brought to Mars aboard Curiosity.
"Even though (SAM) detected organic compounds, first of all we have to demonstrate that they're indigenous to Mars," said Project Scientist John Grotzinger. "Then after that we can engage in the question about whether they represent the background fall of cosmic materials that are organic in composition that fall on the surface of every terrestrial planet."
Only then, he said, can scientists "begin to get into the more complex questions of whether or not this might be some type of a biological material. But that's well down the road for us."
Grotzinger made the comments during a news briefing at the American Geophysical Union's fall meeting in San Francisco.
Widespread speculation that Curiosity had made a major discovery began in the wake of SAM's first soil sample analysis and a National Public Radio interview with Grotzinger, who was reluctant to discuss the rover's findings before the AGU presentation.
Asked about lessons learned from the apparent conflict between public expectation and scientific reality, Grotzinger said "I think 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. We're doing science at the speed of science. We live in a world that's sort of at the pace of Instagrams.
"The enthusiasm that we had, that I had, that our whole team has about what's going on here, I think was just misunderstood. There's not much more to say than that."
Curiosity was lowered to the surface of Gale Crater by a rocket-powered backpack on Aug. 6, kicking off a planned two-year mission to look for organic compounds and to find out whether the red planet has, or ever had, a habitable environment.
The first four months of the mission have been devoted to activating, testing and calibrating its scientific instruments before the rover begins making its way to its ultimate target, the base of a central 3.5-mile-high mound of layered terrain in the center of Gale Crater that is known as Mount Sharp.
Most recently, Curiosity's robot arm has been put through its paces scooping up sandy soil samples from a low dune and depositing them into a pair of on-board mini laboratories, SAM and another known as CheMin, for Chemistry and Mineralogy.
Scientists deliberately picked an average looking dune made up of presumably commonplace, fine-grained soil. Several scoops were processed through the sample acquisition system and then discarded in an attempt to scrub away any traces of Earth's environment. Portions of a third and fourth samples were processed by the CheMin instrument and the fifth by SAM.
"The instrument, SAM, is working perfectly well," Grotzinger said. "It has made this detection of simple organic compounds. We just simply don't know if they're indigenous to Mars or not. It's going to take us some time to work through that. I know there's a lot of interest in that. But the point is, Curiosity's middle name is 'patience' and we all have to have a healthy dose of that."
Paul Mahaffy, the principal investigator for SAM at NASA's Goddard Space Flight Center, agreed, saying "we have to be very careful to make sure both the carbon and the chlorine are coming from Mars. ... There's more work to do."
And even then, he cautioned, the tentative results must be taken in context.
"If we take microbes that are living in some extreme environments on Earth that aren't very abundant and we do this same type of experiment, we see a whole suite of organic structures produced," he said.
"What we're seeing here (on Mars) are some very simple compounds and it's entirley possible they're coming from the very reactive chlorine that's released and picking up carbon from somewhere. We have to try to understand where that carbon is coming from. But the informative thing in really understanding a source of carbon, what we would have to have is a whole variety of compounds."
After completing its initial sample anlysis runs at a sand drift in an area known as Rocknest, Curiosity moved to a new area, known as Point Lake, while the team looks for suitable rocks to serve as test subjects for a powerful drill mounted on Curiosity's robot arm. The drill, intended to provide pristine samples from the interior of targeted rocks, is the final major component of the science package to be tested.
The nuclear-powered rover was not designed to look for signs of past or present life. Rather, its instruments were built to look for the chemical traces of past or present habitability.
"At this point, basically, our car is ready to go," Grotzinger said. "This is a car that comes with a 10,000-page user manual that we also have to write as we read it. That's where the patience comes in."
Engineers hope to complete the drill tests before the Christmas holidays. After that, Curiosity will head for Mount Sharp.
"So we're going to load up the car with the science team," Grotzinger said. "We've gassed it up, checked the oil, we're going to kick the tires around a little bit but then we're ready for our trip and that's when our science mission of exploration really gets into full gear."