Martians, Revisited

Only when it comes to alien life forms can the absence of decent data - the 1976 Viking mission did not not detect any organic molecules - seem so exciting. Here's Sharon Begley, from behind the WSJ firewall:

When scientists announced Monday that the search for life on Mars 30 years ago may not have been quite the bust it has long been portrayed, it didn't mean that the mission had missed any microorganisms, let alone advanced life forms. But it did underline the growing sense that decades of assumptions about extraterrestrial life need serious re-examination.

In 1976, scientists studying data sent back by the Viking landers were quick to dismiss life on Mars. They regarded the results of one intriguing experiment, which hinted at life in the soil of the red planet, the way they would an embarrassing relative who spouts uncomfortable truths. Some things you don't say in polite society, and "Viking found life" became one of them.

Now scientists are taking another look at those data, at a time when the possibility of life elsewhere in the universe seems to grow with every new discovery. Studies on Earth suggest that life can exist in environments long thought hostile to it, and the plethora of life-forming molecules in outer space suggest that the seeds of life are everywhere.

As I reported this week, the two Viking landers conducted three experiments searching for signs of life in the top few inches of Martian soil. One designed to detect metabolism suggested biological activity. The scientist who led the design of that "labeled-release" experiment (so-called because it used radioactively labeled carbon), Gil Levin of Spherix, Beltsville, Md., still argues it "detected living microorganisms."

But other Viking experiments at the time were seen as more authoritative. Scientists assume that life, whether on Earth or Mars, requires organic (carbon-containing) molecules. So, when experiments failed to find organic molecules in the Martian soil, almost all scientists dismissed the labeled-release experiment as finding exotic chemistry, not biology.

Some three decades later, more-sophisticated instruments have shown that the Vikings couldn't have detected organic molecules even if any were present. When scientists fed soil from the Atacama Desert of Chile and Peru, and the Dry Valleys of Antarctica, experiments like those the Vikings conducted came up empty. Yet, new techniques show the samples contained 10 to 1,500 micrograms of carbon per gram.

"If we knew this 30 years ago, our interpretation of the Viking results would have been very different," says Rafael Navarro-González of Mexico's National Autonomous University, who led the study published in Proceedings of the National Academy of Sciences.