On Mars, Organics Are Hard to Find

And now we know the reason why.

Curiosity's view of rock strata at the foot of Mt. Sharp on Mars. Finding signs of Martian life will require scientists to keep an open mind. (NASA/JPL)

The near absence of organic compounds on Mars has long been a conundrum to those searching for possible life on the Red Planet. Such compounds should exist on or near the surface, if only from having arrived there with cometary infall. (We see, for example, organic compounds in Martian meteorites found on Earth). But when the Viking lander detected chlorinated organic compounds on Mars decades ago, they were interpreted at the time as terrestrial contamination. Only recently, with the Curiosity Rover’s discovery of organic compounds, has it become accepted that there are organic compounds indigenous to Mars, although it’s still not clear whether these are of biological origin.

In a new paper, Wren Montgomery from the Imperial College in London and colleagues explain why it is so difficult to detect organic compounds in the Martian soil. Oxidizing compounds such as perchlorates mask any indigenous organics on Mars given the current method used to detect organic compounds—called pyrolysis—which involves the decomposition of soil material at high temperatures.

The scientists offer a solution, however: They suggest modifying the detection method by simply removing perchlorate with an aqueous extraction method prior to pyrolysis. They show that this worked in similar soils from the Atacama Desert, which contained biomarkers indicative of cyanobacteria. Based on their experience, Montgomery and her co-authors recommend that previous test results showing no organics, or only very small amounts, in Martian soils containing high levels of oxidizing compounds should be re-examined.

This seems to me one of those cases in which a paradigm literally blinds researchers to the presence of anomalies. That happens quite often, according to a new paper by Carol Cleland from the University of Colorado in Boulder. In fact, she says, instead of trying to come up with a universal definition of life–which cannot be done when we only know the kind that exists on Earth–we should look for anomalies, or phenomena that “shouldn’t be there” given our current Earth-centric understanding of biological and non-biological processes. Only that way can we make leaps in understanding, and actually have a chance of finding life as we don’t know it.

In her paper Cleland provides several fitting examples, from the discovery of the planet Uranus to the Viking life detection experiments, where progress was delayed because scientists were too stuck in their old paradigms. When faced with the puzzle of no organics detected (apparently) by Viking, project scientist Gerald Soffen insisted, “No bodies, no life”.

As Cleland says, it may be difficult to determine whether a puzzling phenomenon on another planet is the product of biology or not. But any observed anomaly should be a priority for further investigations. The new research by Montgomery and colleagues helps to explain why it is was so difficult to detect organic compounds on Mars, and how that problem can be overcome on future missions. And that makes it a real step forward in settling one of the major scientific questions of our time.


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