In 1976, the National Aeronautical Space Agency (NASA) launched the Viking program, sending space probes to Mars to determine whether there was life on the red planet. Thirty-six years later the debate about life on Mars is not over, but research conducted in part at the University of Southern California (USC) offers more proof that life may exist on this neighboring world.
The landing site of Viking 1 on Mars in 1977, with trenches dug in the soil for the biology experiments. Credit: NASA/JPL
Joseph D. Miller, associate professor of cell and neurobiology at the Keck School and colleagues conducted an independent analysis of the labeled release (LR) data from the Viking landers 1 and 2. The researchers applied mathematical measures of complexity to the data, which indicate a high degree of order that is more characteristic of a biological rather than a non-biological, purely physical process.
The research was published online April 9, 2012, in the International Journal of Aeronautical and Space Sciences.
In the experiments, the Viking landers dropped on Mars about 4,000 miles apart, scooped up soil samples and applied a radiolabeled nutrient cocktail to the soil. If microbes were present in the soil, they would likely metabolize the nutrient resulting in the release of CO2 or possibly methane (CH4). The active experiments did indicate metabolism, and control experiments on sterilized soil samples produced little or no gas release. But due to lack of support from two other Viking experiments that did not find any organic molecules in the soil, most scientists believed the LR data had been compromised by a non-biological oxidizing property of Mars soil.
Miller and colleagues did not accept this interpretation, and over the last six years applied measures of mathematical complexity to the data from active and control Viking data, as well as terrestrial biological and non-biological data sets. Not only did the active Viking LR experiments exhibit higher complexity than the control experiments, but the active experiments clearly sorted with terrestrial biological data series whereas the Viking LR control data sorted with known terrestrial non-biological data.
“To paraphrase an old saying, if it looks like a microbe and acts like a microbe, then it probably is a microbe,” said Miller, who is a neuropharmacologist, but also studies circadian rhythms at USC and is an author on the research. “The presence of circadian rhythmicity and a high degree of mathematical complexity or order in the LR data most likely means Viking discovered microbial life on Mars over 35 years ago.”
Without a protective atmosphere similar to Earth’s, life on Mars is more likely to exist underground, where it is safe from ultraviolet radiation, Miller said. If life does exist on Mars, the knowledge could unlock secrets of life here on Earth.
“We have only one example of life in the universe — we are it,” said Miller. “Finding another example of life somewhere else could be the biggest step forward in biology since the delineation of the genetic code by Crick and Watson.”
Though the research offers tantalizing proof, much more is needed. Miller thinks it’s time to send a probe back to Mars to make the definitive determination.
“This research is not a smoking gun,” he said. “A smoking gun would be taking a picture under a microscope of Mars bacteria. But the case is getting stronger. We know there is sub-surface water ice, and perhaps liquid water in regions that seem to release methane gas into the atmosphere. Water is necessary for life and methane is a potential signature of biology. There’s enough circumstantial evidence that strongly suggests NASA or the European Space Agency should consider explicit life detection experiments on Mars.”
Joining Miller in the new research is Viking LR principal investigator Gilbert V. Levin, adjunct professor, Arizona State University, Giorgio Bianciardi, researcher in human pathology and oncology at University of Siena, Italy, and Patricia A. Straat, co-investigator on the Viking LR studies (retired).