for National Geographic News
As three separate missions journey to Mars this month to search for signs of life, one scientist claims that he already proved there's life on the red planetin 1976.
Gilbert Levin, who was in charge of a life-detection experiment on NASA's historic Viking mission in 1976, says his biology experiment detected activity in the Martian soil.
"We obtained positive data corresponding with all the pre-mission criteria, which proved the existence of microbial life in the soil of Mars," Levin, who is the CEO of biotechnology firm Spherix, Inc., said in a telephone interview from his company's headquarters in Beltsville, Maryland.
NASA saw it differently. After scientists conducted additional experiments, which contradicted Levin's initial findings, the space agency concluded that Mars is a dead planet.
But the debate didn't end there, and a controversy over whether or not there's life on Mars has been brewing ever since. Levin, who is very critical of NASA, contends that liquid water exists on the surface of Mars, and he accuses the space agency of ignoring the evidence for life.
Little Green Men
Mars has fascinated people for centuries. In ancient Assyria, the red planet was known as the "shedder of blood." The Vikings called it the god of war. In more recent times, Mars became the favorite home of aliens in science fiction stories.
Mars is the planet in our solar system that most closely resembles Earth. It has a similar temperature; an atmosphere, which is thinner than Earth's, but may have been thicker at one time; and a rocky surface, making it easier for life to gain a foothold. It also has polar icecaps.
We know there are no little green men running around Mars. But primitive life could survive around hydro-thermal vents near the planet's surface. Today it's perhaps too cold for life to exist there. But organisms may have thrived in the past.
Mars was a completely different place around the time life started on Earth 3.5 to 4 billion years ago. Scientists believe the planet was like Earth, with water and warm, but that it changed, losing much of its water and turning cold and hostile.
During the Viking mission, Levin was in charge of the life-detection experiment, known as "Labeled Release," in which he used nine samples of Martian soil to test for metabolic activity.
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