Did Viking Probes Miss Life on Mars?

Oct. 24, 2006 — NASA's first experiments to look for organic matter on Mars may not have been sensitive enough to detect life, concludes a team of researchers studying Martian-like soils in remote regions of Earth.

The twin Viking probes landed on the surface of Mars in 1976 to search for signs of past or present life. One test involved the rapid heating of soil samples so they vaporized, leaving trace molecules to be analyzed by spectrometers.

No biological materials were found and NASA abandoned ground exploration of Mars for more than 20 years.

But Rafael Navarro-Gonzalez, a researcher with University of Mexico in Mexico City, and colleagues have another explanation for the Viking results: The life-detection experiment could have missed low levels of biological activity.

The researchers built their theory on studies conducted with Viking-type instruments in some of Earth's harshest environments: the Antarctic Dry Valleys, the Atacama desert of Chile and Peru, and deserts in Libya.

Soil samples in those locations contain trace amounts of materials that Viking would have missed.

Despite inhospitable conditions, soil samples from many of the team's test sites showed signs of life.

In 2004, the Mars rover Opportunity discovered an iron-rich mineral called jarosite on the surface of Mars, pointed out Navarro-Gonzalez. The same mineral is known to exist in Spain's river Rio Tinto.

"So I decided to collect sediments from this river, which has a very acidic pH...high levels of iron and yet the presence of microorganisms from the three domains of life," Navarro-Gonzalez told Discovery News.

The team also discovered that iron-rich soils could oxidize organic molecules into carbon dioxide, further reducing the amount of material left behind.

This finding also might explain the high levels of carbon dioxide the Viking instruments measured in the Martian soil, say the researchers, whose work appears in this week's issue of the Proceedings of the National Academy of Sciences.

"The Martian surface could have several orders of magnitude more organics than the stated Viking detection limit," the authors wrote.

While most scientists believed Viking's findings to be clear-cut, others were not convinced. Gilbert Levin, one of the mission's lead scientists, has long maintained that his life-detection experiment found living microorganisms in the soil of Mars.

Researchers now also believe that the best place to look for signs of life is underground, which is more protected from solar radiation. NASA's current approach to Mars exploration is to look for signs of past and present-day water, which is believed to be necessary to support life.

Over the past 10 years, NASA has dispatched a series of increasingly sophisticated probes to Mars to survey minerals and geologic formations from above the planet's surface, and to analyze soil and rock chemistry with rovers on the ground.

"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," Navarro-Gonzalez and his colleagues concluded.

NASA's next two landers, the 2007 Phoenix mission and the 2009 Mars Science Laboratory, both include instruments to analyze soil samples for water, carbon dioxide and organic materials.

Europe's ExoMars mission, slated for launch in 2011 or 2013, is designed to characterize the biological environment on Mars.