The two Viking spacecraft each took four instruments designed to answer one big question, Lee says, are there signs of life on Mars?
There were three biological experiments and one organic chemistry experiment, and of course, Viking 1 got to run them first. “On Viking 1, one of the biology instruments showed what you would call on the Earth if you saw it an absolute positive, another likely positive, and the third one undecided,” Lee says.
But the organic chemistry experiment, designed to find the types of organic compounds, the debris, or detritus scientists always find in the presence of life on Earth, turned up zilch. Some scientists persisted in claiming the biology experiments had shown evidence for life, while others, citing the chemistry experiment, declared Mars barren.
“The absence of any organic material on the surface of Mars, on any of the places that we looked, led people to the conclusion that Mars was lifeless,” Lee says. “That was a wrong conclusion.”
It’s not that Lee believes there were definitive signs of life in the Viking data. Still, neither was there a careful, systematic investigation into whether the claim that Mars was, in fact, lifeless was really true. “In other words, absence of evidence is not evidence of absence. That's a very, very famous thing that Carl Sagan and I coined in Cosmos,” Lee says. “What we found with Viking 1 was the absence of evidence of life — and ambiguity.”
That’s where Viking 2 comes in. Same spacecraft, same experiments, but a different location. Perhaps the results would be different this time?
“Again, we had the same results,” Lee says. “No organic material.”
But in the final days of the Viking 2 mission, as the science team began to get a little desperate to get any additional data, Carl Sagan and others on the science team had an idea, according to Lee.
Maybe ultraviolet radiation was breaking down any ancient organic compounds on the surface. If Viking 2 could use its robotic arm to push a rock out of the way, perhaps in the soil underneath, undistributed for billions of years, there could be signs of life.
“To me, it was the most exciting part of Viking 2,” Lee says. “We took the surface sampler arm, and we pushed a huge rock out of the way, dug underneath it, took the soil, analyzed it — and got the same results.”
Lee wonders what might have been. Since Viking 2, meteor impacts in the Utopia Planitia region have exposed ice beneath the surface. That Mars might have water ice hidden beneath its russet dust was a major finding of the Mars Odyssey orbiter in 2001, Lees says, but it wasn’t even imagined at the time of Viking. If the spacecraft could dig just a little deeper, the whole history of planetary exploration might have been radically different.