Were Viking landers blind to life?

The Viking landers may have missed potential signs of life when they explored Mars in 1976, an international research team asserts.

NASA's two unmanned Viking craft landed on Mars, took pictures, and conducted a variety of experiments. While some of the data suggested biological activity in the Red Planet's soil, the chemical analyses didn't turn up organic compounds, expected to be present if there were life there.

The data became the basis for arguments against current or past life on Mars, says Rafael Navarro-Gonzalez, a chemist at the National Autonomous University of Mexico in Mexico City.

The Viking landers used a technique called thermal volatilization-gas chromatography-mass spectrometry (TV-GC-MS) to analyze the soil. In that process, an instrument vaporizes a soil sample, separates the chemical fragments produced, and then identifies those constituents.

To review the technique's effectiveness, Navarro-Gonzalez and his colleagues used TV-GC-MS on Earth soils that share features with soil on Mars. They tested arid samples from Chile, Egypt, and Antarctica and iron-rich soils from Spain and Hawaii. The researchers also tested all the samples with a different technique for measuring organic matter.

In tests of the arid-soil samples, the latter technique revealed small amounts of organic compounds. But a TV-GC-MS analysis done according to the landers' protocol failed to detect those compounds.

The iron-rich soils also contained organic compounds. However, the researchers found that the iron causes a reaction during TV-GC-MS analysis that converts the compounds' carbon to carbon dioxide. This could explain why the landers detected carbon dioxide but not organic material, notes Navarro-Gonzalez.

"The question of whether there is life on Mars remains open," he adds.

The researchers describe their work in the Oct. 31 Proceedings of the National Academy of Sciences.--A.C.