Thirty-four years after NASA's Viking missions to Mars sent back results interpreted to mean there was no organic material - and consequently no life - on the planet, new research has concluded that organic material was found after all.
The finding does not bring scientists closer to discovering life on Mars, researchers say, but it does open the door to a greater likelihood that life exists, or once existed, on the planet.
"We can now say there is organic material on Mars, and that the Viking organics experiment that didn't find any had most likely destroyed what was there during the testing," said Rafael Navarro-Gonzalez of the National Autonomous University of Mexico.
"For decades NASA's mantra for Mars was 'follow the water' in the search for life, and we know today that water has been all over the planet," he said. "Now the motto is 'follow the organics' in the search for life."
The original 1976 finding of "no organics" was controversial from the start because organic matter - complex carbons with oxygen and hydrogen, which are the basis of life on Earth - is known to fall on Mars, as onto Earth and elsewhere, all the time. Certain kinds of meteorites are rich in organics, as is the interstellar dust that falls from deep space and blankets planets.
The new results, published in the Journal of Geophysical Research-Planets and highlighted Friday in a NASA news release, flow directly from a discovery made by NASA's Phoenix lander in 2008.
Mary Voytek, senior scientist for astrobiology at NASA, said the findings demonstrate the ever-present risk of reaching "false negatives" in space based on limitations of the equipment used and of the scientists' understanding of conditions beyond Earth.
She said the research does not fully knock down the original "no-organics" conclusion because the new experiment was done using desert soil from Earth, which might behave differently from seemingly similar Martian dirt. But she said the research does put another "significant chink" in the no-organics position.
The new research examined the effects on organics of a compound that Phoenix unexpectedly found at its landing site on northern Mars.
The discovery of the highly reactive chemical perchlorate led NASA's Christopher McKay, an astrobiologist at the Ames Research Center, and Navarro-Gonzalez to test whether the perchlorate had skewed the Viking results that showed no sign of organic material on Mars.