Joseph D. Miller, Ph.D.
In 1976, the National Aeronautics and Space Administration (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.
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
“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
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
“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).