The soil on Mars may indeed be teeming with microbes, according to a new interpretation of data first collected more than 30 years ago.
The search for life on Mars appeared to hit a dead end in 1976 when Viking landers touched down on the red planet and failed to detect biological activity.
There was another flurry of excitement a decade later, when Nasa thought it had found evidence of life in a Mars meteorite but doubts have since been cast on that finding.
Today, Joop Houtkooper from Justus-Liebig-University in Giessen, Germany, will claim the Viking spacecraft may in fact have encountered signs of a weird life form based on hydrogen peroxide on the subfreezing, arid Martian surface.
His analysis of one of the experiments carried out by the Viking spacecraft with a geophysicist, Dirk Schulze-Makuch of Washington State University, Pullman, suggests that 0.1 percent of the Martian soil could be of biological origin, he will tell the European Planetary Science Congress in Potsdam, Germany.
That is roughly comparable to biomass levels found in some Antarctic permafrost, home to a range of hardy bacteria and lichen. “It is interesting because one part per thousand is not a small amount,” Houtkooper said yesterday.
“We will have to find confirmatory evidence and see what kind of microbes these are and whether they are related to terrestrial microbes. It is a possibility that life has been transported from Earth to Mars or vice versa a long time ago.”
The discovery of microbes on Earth that can exist in environments previously thought too hostile has fuelled debate over extraterrestrial life.
Houtkooper believes Mars could be home to just such “extremophiles” – in this case, microbes whose cells are filled with a mixture of hydrogen peroxide and water.
Such a mixture would provide at least three clear benefits to organisms in the cold, dry Martian environment.
Its freezing point is as low as -56.5 C (depending on the concentration of peroxide); below that temperature it becomes firm but does not form cell-destroying crystals, as water ice does; and hydrogen peroxide is hygroscopic, which means it attracts water vapour from the atmosphere – a valuable trait on a planet where liquid water is rare.
Houtkooper believes their presence would account for unexplained rises in oxygen and carbon dioxide when NASA’s Viking landers incubated Martian soil.
He bases his calculation of the biomass of Martian soil on the assumption that these gases were produced during the breakdown of organic material.
Hydrogen peroxide is also a powerful oxidant. When released from dying cells, it would sharply lower the amount of organic material in their surroundings.
This would help explain why Viking’s gas chromatograph-mass spectrometer detected no organic compounds on the surface of Mars.
This result has also been questioned recently by Rafael Navarro-Gonzalez from the Universidad Nacional Autonoma de Mexico in Mexico City University of Mexico, who reported that similar instruments and methodology are unable to detect organic compounds in places on Earth, such as Antarctic dry valleys, where we know soil microorganisms exist.
The twin spacecraft, Viking 1 and Viking II, landed on the Red Planet in 1976. They were equipped with detectors designed to test the Martian soil for evidence of life.
The main instrument, called the TV-GC-MS assay, rapidly heated and vaporised soil for analysis by a spectrometer.
Dr Navarro-Gonzales concluded: “The fact that no organic molecules were released .. during the analysis of the Mars soils does not demonstrate that there were no organic materials on the surface of Mars..”
“We suggest that the design of future organic instruments for Mars should include other methods to be able to detect extinct and or extant life.”
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