By Leonard David
updated 10/23/2012 6:32:37 PM ET
There’s growing buzz about data gleaned by NASA’s Curiosity rover on Mars, specifically over the issue of methane detection on the Red Planet.
On one hand, methane can be geological in origin. But then there’s the prospect that the gas is biotic, or caused by living organisms — meaning it could be the gaseous residue of long-extinct microbes or even the output of Martian organisms alive and well today.
Curiosity is toting the Sample Analysis at Marsinstrument suite, or SAM, an onboard lab that accounts for more than half of the science payload on the 1-ton rover. Though SAM's components would ordinarily fill a laboratory here on Earth, they have been miniaturized to roughly the size of a microwave oven in order to fit inside the robot.
SAM's duty is to analyze gases that are either "sniffed" directly from the Martian atmosphere (which it has done several times) or extracted from soil or powdered rock samples by heating or chemically treating the samples.
Provided by NASA’s Goddard Space Flight Center, SAM is on the search for compounds of the element carbon, including methane, that are associated with life. SAM will also explore ways in which those compounds are generated and destroyed in the Martian ecosphere. [Mars Methane: Could It Mean Life? (Video)]
According to Goddard's SAM website, determining the presence or absence of organic molecule would yield important science results. Either presence or absence would provide important information about the environmental conditions of Gale Crater, where Curiosity touched down on Aug. 5.
If SAM does find organic material, the next step would be to determine the origin and the nature of preservation of the molecules. But if SAM does not find organic material, a better place to look might be below the surface.
"The key question about methane on Mars is not its presence, but its variability," said Chris McKay, space scientist and Mars specialist at NASA's Ames Research Center in Mountain View, Calif. As shown by many engaged in the methane-on-Mars issue, it is known that organics are falling onto the surface of Mars and that ultraviolet light produces methane from them, he told Space.com" But what was surprising in the Mars Express results and the Earth-based observations was the variability," he added, referring to the European Space Agency's Mars Express orbiter. "Methane on Mars should have a lifetime of 300 years and should not be variable. If it is variable, this is very hard to explain with present theory. It requires unexpected sources and unexpected sinks."
In terms of Curiosity’s SAM instrument, McKay said that the key will be the tracking of whatever methane is seen over time.
"If it’s constant, then this can be reconciled with normal processes and a meteoritic source of organics. If it’s highly variable, then all bets are off." [5 Bold Claims of Alien Life]
Waiting to exhale
"Methane should be there," said astrobiologist Dirk Schulze-Makuch of Washington State University in Pullman. One of his research interests focuses on the interaction of microbes with their natural geological environment in an aqueous medium.
Schulze-Makuch says his view is based on three independent earlier studies, with methane usually associated with biological activity or ancient biology activity.
"Methane is really quite a rare gas in hydrothermal/volcanic exhalations; thus a methane detection with the rover would be exciting and could point to biology, especially if detected in relatively large amounts," Schulze-Makuch told Space.com.
"Even more exciting," Schulze-Makuch said, "would be if the carbon in the methane has an isotopic fractionation that is consistent with biology. If the methane is produced by organisms — for example, metabolism — then we expect a shift to the lighter isotopes. In essence because life is lazy, same effect, with less work compared to inorganically produced carbon."
Whether any Mars methane detections would be sufficiently high to determine the isotope ratio, Schulze-Makuch said, is a wait-and-see moment. "But it would be very exciting. To try and determine the isotopic fractionation and a good inorganic baseline for carbon would be the next step in my view." [7 Biggest Mysteries of Mars]
Chizek told Space.com that she too is eager to see the Curiosity results announced.
Chizek is working on computer simulations using the NASA/Ames Mars Atmospheric General Circulation Model to replicate trace gases in the Martian atmosphere. Her modeling research enables the tracing back of detected methane to its source location to see whether it is coming from something like a volcanic source, water surface chemistry interaction or bacteria living on or near the surface.
Chizek said that there have been several claims of methane detection in the past decade, from Mars-orbiting spacecraft as well as telescopic observations from Earth. But those claims tend to be controversial, she said, because observations suggest that it’s varying in abundance on a very quick time scale, which is unexpected.
Detecting methane on Mars could lead to evidence of life, as roughly 95 percent of the methane in Earth’s atmosphere is a product of biology, Chizek said. In her recent talk at the DPS meeting, she underscored the volume and significance of methane on Mars by using a very Earthly creature that produces the gas: cows.
So how many cows would be required to equal the amount of methane that scientists have observed on Mars? "Depending on which observations I am looking at, that number is close to 5 million cows, or roughly 200,000 tons of methane production per year," Chizek reported.