Mars shows plenty of evidence for flowing water on its surface, as in the case of these channels in Newton Crater. Does this mean that the Red Planet ever supported life? Photo Credit: NASA

The Search for Alien Life Part 1: Where are the Martians?

By David Darling

On July 20, 1976, a 572-kilogram spacecraft, supported on three sturdy legs, touched down on the orange sands of Mars in the western part of Chryse Planitia. Six weeks later, its sister craft made landfall about 200 kilometers west of the crater Mie in Utopia Planitia. The twin Viking landers were the first purpose-built attempts to hunt for life on another world.

Each carried a miniature laboratory containing experiments designed to show if Martian microbes were alive in the soil of the Red Planet. Initially, there was great excitement because a couple of the experiments gave signs that soil samples delivered to the onboard lab by the Viking robotic arm were feeding on the nutrients offered to them. But as time went on, the results became more puzzling—something was definitely active in the soil, but was it chemical or biological? Opinion shifted emphatically the chemical way, when an instrument called the gas chromatograph–mass spectrometer (GC-MS) failed to detect any trace of organic (carbon-bearing) compounds in the soil samples.

A few scientists, notably Gil Levin, the principal investigator of one of the Viking experiments, continued to argue that Viking really did find life. Serious doubts were cast on the sensitivity of the GC-MS to low concentrations of organics, and it remains a fact that not all Viking’s data can be squared with a simple chemical interpretation

Read more: The Search for Alien Life Part 1: Where are the Martians? « AmericaSpace.

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