Viking Mission May Have Missed Mars Life, Study Finds

Brian Handwerk
for National Geographic News
October 23, 2006
The Viking Mars mission may have missed signs of life when it visited the red planet 30 years ago, a new study suggests.

If future missions are to set the record straight, the study's authors add, scientists may need to change the ways in which they search.

NASA's Viking Mission to Mars put two landers on the red planet in 1976. Their experiments uncovered mysterious chemical activity in the Martian soil but no clear evidence of life.

Now scientists suggest that telltale signs of life could have been there all along, but Viking's testing methods were not robust enough to recognize them.

"We simulated these [tests] that Viking did 30 years ago, this time in extreme regions of our own planet," said Rafael Navarro-Gonzalez, of the National Autonomous University of Mexico in Mexico City.

"We found low levels of organic compounds in those soils, but we cannot detect them by the same technologies used by the Viking mission."

Navarro-Gonzalez's report is published in the current issue of the Proceedings of the National Academy of Sciences.

Mars-Like Earth Environments

The Viking landers performed chemical analyses by heating Martian soil samples to vaporize their contents into a gas.

They examined the gas by spectrometer—a device that measures the wavelengths emitted by chemicals in the gas—which revealed no clear evidence of microorganisms in the soil.

But Navarro-Gonzalez's team duplicated the Viking tests in Mars-like Earth environments and found that they missed present signs of life in soil samples from Antarctic dry valleys, the Atacama Desert of Chile and Peru, and other locales.

(See a National Geographic magazine feature on the Atacama Desert: "The Driest Place on Earth".)

Navarro-Gonzalez suggested several reasons that Viking could have failed to detect organic materials.

The Viking landers heated Martian soil to scorching temperatures of up to 500 degrees Celsius (932 Fahrenheit) to vaporize its contents.

But, Navarro-Gonzalez stresses, even at such high temperatures many organic compounds are just too stable to be turned into a gas, so they may have been undetectable.

"Another possibility is that the presence of iron oxidizes these organic compounds to carbon dioxide, and this prevents detection by the mass spectrometer," Navarro-Gonzalez explained.

Viking did detect significant levels of carbon dioxide—though most scientists have maintained that it has an inorganic source or was absorbed from the planet's atmosphere.

Scientists Discover Mars-Friendly Microbes

Revisiting Viking's tests could challenge future Mars missions to step up technologies in their search for life.

NASA's Mars Science Laboratory, scheduled to blast off in autumn 2009, should pack a more potent scientific punch.

Paul Mahaffy, of NASA's Goddard Space Flight Center in Greenbelt, Maryland, is principal investigator for the mission's sample and analysis instrument.

He notes that the mission should overcome Viking's detection difficulties and enjoy some huge advantages that will advance the search for life.

Orbiters will provide geological and mineralogical data to pinpoint the most promising surface sites to explore.

"This, combined with the ability of Mars Science Laboratory to rove several kilometers and to core into the interior of rocks, makes the search for organics much more powerful than was possible in the past," Mahaffy said.

Possible Martian life-forms now include a newly discovered class of microorganisms on Earth that can survive and even reproduce at 30 degrees Fahrenheit (minus 1 degree Celsius)—below the freezing point of water.

The cold-resistant life-forms fascinate scientists, because frigid planets like Mars are far more common in our galaxy than warmer worlds.

(See Photo in the News: "Ice Lake Found on Mars" [August 2, 2005].)

"Our results show that the lowest temperatures at which these organisms can thrive fall within the temperature range experienced on present-day Mars and could permit survival and growth, particularly beneath Mars's surface," said Neill Reid, an astronomer at the Baltimore-based Space Telescope Science Institute.

"This could expand the realm of the habitable zone, the area in which life could exist, to colder Mars-like planets."

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