An analog of martian land, the Rio Tinto in Spain maintains a microbial community, however Viking Lander tests on its sediments failed to detect organic matter.
Credit: Rafael Navarro-González
SYDNEY: The first probes to land on Mars may have missed evidence of life, according to a new international study.
"The question of whether organic compounds exist on the surface of the planet Mars was not conclusively answered by the [experiments] carried out by the Viking Landers," according to the researchers, who publish their findings today in the U.S. journal, Proceedings of the National Academy of Sciences.
"Furthermore, it is important that future missions to Mars include other analytical methods to search for extinct … or extant life in the martian soil," they write.
In 1976 two NASA robotic spacecraft, Viking 1 and Viking 2, landed on Mars with a variety of tests on board. None of the experiments performed at either landing site detected organic matter, even though the soil was extremely reactive and suggested the possible presence of biological activity.
To test for organic matter, the martian soil was rapidly heated to 500°C so that larger molecules in the soil sample were broken down into smaller molecules. The resultant fragments were then separated and analysed to find their mass and charge. This experiment, officially named TV-GC-MS, allows scientists to identify organic matter that may have been present in the original soil sample. No organic matter was found on the surface of Mars using TV-GC-MS.
In the study published today, the Viking experiments were repeated using samples from Earth. Samples were taken from dry deserts (Antarctica, Chile/Peru and Egypt), wetter deserts (Chile/Peru and the USA), and soils with a mineral content thought to be most similar to martian soil (Spain and the USA).
Unlike the Viking Landers' experiements, this study also directly measured the amount of organic matter in the soil. In addition, the soil was heated to 750°C in a TV-GS-MS experiment. The researchers concluded that, in some cases, heating the samples to only 500°C was not sufficient to release the organic matter.
In soil samples containing a small amount of organic matter but a large amount of iron (martian soils also contain a large amount of iron) the iron interacted with the organic matter while the sample was being heated, sometimes preventing the organic matter from being detected at all.
"Our results influence the interpretation of the Viking TV-GC-MS data. The fact that no organic molecules were released by this analytical treatment during analysis of the Mars soils does not demonstrate that there were no organic materials on the surface of Mars."
Three future missions to Mars, two from the U.S. space agency NASA and one from the European Space Agency, are planning to test for organic matter using similar experiments.
"Because of the simplicity of sample handling, TV-GC-MS is still considered the standard method for organic detection on future Mars missions," the researchers write.
According to scientists, Mars was warm and wet for its initial 500 to 1,000 million years. The discovery of past liquid water on Mars has marked the planet as a prime candidate in the search for life beyond Earth.
