Debate on Mars life rages long after Viking
By Richard Stenger
(CNN) -- The mightiest probe ever to land on another planet settled down on Mars on this day 25 years ago, igniting a scientific firestorm that still rages today -- Does the red planet possess life?
Officially, NASA concluded that the Viking 1 and its sister ship the Viking 2, which landed on the other side of the planet weeks later, did not uncover signs of life after scooping, baking and dissecting the iron-rich soil.
But a handful of scientists, including some who designed the Viking life experiments, maintain that the test results came back positive.
One matter that is not the subject of debate: The Viking twins were the most powerful spacecraft ever to land on another planet. Each Viking boasted an orbiter, a lander and a nuclear energy supply, allowing the satellites and ground ships to beam back data from the red planet for six years, unlike their contemporaries, which sputter out after months because they have less durable electrical supplies.
Flush from the success of the Apollo mission that placed men on the moon, NASA spent $1 billion on the Viking program, the first to place probes on Mars.
"The Viking laboratories were an order of magnitude more expensive and compelling than the missions we are now planning," said Jim Garvin, a junior Viking researcher who helped on the imaging team.
'Cadillac of robotic missions'
"It was the Cadillac of robotic missions. Today we bite off a little less with each mission," said Garvin, now the chief Mars scientist for NASA.
"Viking was an armada in its own right," echoed Michael Malin, who manages the cameras aboard the Mars Global Surveyor, a NASA satellite currently orbiting the red planet.
The Vikings expired decades ago, but they are still proving invaluable to science. "They still have things to teach us. There's a gold mine of data there. People are still digging in the treasure trove," Garvin said.
'More likely than not we detected life'
Perhaps the most controversial Viking legacy involves the work of Gilbert Levin, a maverick scientist who came up with a different conclusion than NASA establishment on the Viking data.
In his biology experiments, a soil sample was mixed together with radioactive nutrients. If life were present, it would consume the food and leave gaseous traces of its metabolism, which radioactive monitors would then detect.
To make sure it was a biological reaction, the test would be repeated after cooking the soil well above the boiling point of water. Such a baking would prove lethal to known life.
If there was a measurable reaction in the first and not the second sample, then the Viking scientists could deduce that some biological force was at work in the soil. That is exactly what happened.
"I just said that the results we got were consistent with the presence of life," Gilbert said. Eventually, he strengthened his conclusion.
"I determined that it is more likely than not that we detected life. That mild statement caused a storm of criticism," Gilbert said.
A variety of other Viking experiments came back showing negative responses for life and many planetary researchers take exception to Levin's findings.
'It's just not convincing'
"The small changes (in Levin's test results) just don't fit anything else we know about the Mars surface and therefore it seems implausible that they could represent a biological process," said David Deamer, a space biologist at the University of California, San Diego.
"Gil (Levin) has one small piece of a larger puzzle. By itself, it could be explained by a biological process. But add all the weight of the other observations, and it's just not convincing."
Undaunted, Levin thinks NASA's reluctance to pursue his line of research stems from political fears.
"NASA decided to proceed cautiously (with the interpretation of Viking data). If they said there was life and later found there wasn't, they would have egg all over their face," he said.
A Mars meteorite found in Antarctica with hints of microfossils, pictures from the Mars Global Surveyor that suggest surface water in the recent past, and a flurry of red planet research since the Viking missions have encouraged biologists to consider seriously the possibility that Mars now harbors simple life forms.
Could one test settle it all?
But unlike the Vikings, the NASA landers currently planned for Mars will not look for direct signs of life. They will rove, dig rocks, shoot video and study the geology, but none has biological experiments planned.
NASA managers explain the absence of life tests with a circuitous discussion of the complexity of Mars and the necessity to take small steps before big ones.
The European Space Agency decided to include a suite of biological experiments on its 2003 lander anyway. But will it and other missions tell us within a generation whether life is really there?
Levin thinks he knows how to find the answer. All known life on Earth prefers so-called right-handed sugars and left-handed amino acids. So researchers should repeat variations of his 1976 labeled release experiment, using those sugars and amino acids in one test. And in another, they should use their mirror images -- left-handed sugars and right-handed amino acids.
"If there's life on Mars, it would have the same preference," he said. Should the results mimic what life on Earth would do, "there's not a scientist around who would disagree that this was proof of life," he said.
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