Viking 1 & 2
The Viking project was initiated in 1968 to undertake the first robotic landing on Mars. Each of the two Viking spacecraft was composed an orbiter designed to map the entire surface of Mars, and a lander with a sophisticated biological laboratory onboard to search for evidence of biological activity in the soil.
The Viking mission was: “To increase significantly man’s knowledge of the planet Mars through orbital observations by the orbiter as well as by direct measurements made by the Lander during Martian atmospheric entry, descent, and landing. Particular emphasis was placed on obtaining biological, chemical, and environmental data relevant to the existence of life on the planet at the present time, at some time in the past, or the possibility of life existing at a future date.”
Viking tried to answer a question that mankind has been struggling with thousands of years – Is there Life on Mars? To put it another way, are we alone in the Universe, or are there other planets that may harbor life as the Earth does? If evidence of life on Mars could be found, even single-celled life that lived millions of years ago, then life is not unique to our planet. Indeed, the universe could be teeming with life.
Viking 1 was launched on August 20, 1975 and Viking 2 on September 9, 1975, both using Titan III/Centaur launch vehicles. The journey took 10 months and was uneventful. Viking 1 entered Mars orbit on June 19, 1976 and began taking pictures of possible landing sites. The landing sites were the subject of much debate in NASA, since Mariner 9’s pictures of the surface only had a resolution of 100 yards, and while the Viking orbiter’s were better, they still could not see something as small as a boulder that could damage the lander. Mission planners, while wanting to pick sites which would give good science results, found themselves making conservative choices with the billion-dollar mission. The tentative Viking 1 landing site was in Chryse Planitia, a region where channels carved by flooding empty into the northern lowlands. Viking 2 was to set down in Cydonia, which was far north enough that liquid water might be present.
Viking 1 was scheduled to land on July 4, 1976 to help celebrate the nation’s bicentennial. But, large craters were seen at the proposed landing site and it took mission planners a couple of extra weeks to find another suitable site at Chryse Planitia. Viking 2’s site was also changed from Cydonia, to a more flat region known as Utopia Planitia. It’s interesting to note that Cydonia is the location of the “Face on Mars” (discovered by the Viking orbiters) as well as other enigmatic landforms.
Viking 1 landed on July 20. Nervous NASA engineers and an expectant public waited as the first picture from Mars resolved themselves line-by-line on the television screen. The image showed a rocky, desert-like landscape and the lander’s footpad was covered with red dust. As NASA Astronomer Carl Sagan later wrote, “This was not an alien world.” I knew places like it in Colorado and Arizona and Nevada. Mars was a place.
Shortly after it landed, Viking’s experiment packages went to work. A robot arm scooped up some soil and deposited it into several experiment packages on the lander. Scientists back on Earth were amazed when they began getting results almost immediately. One experiment could measure gases that biological organisms would give off, and it produced oxygen after only a couple of hours. Later it was argued that it was only a chemical reaction because the surface of Mars is covered with oxidants, substances that react with water to product oxygen.
Another package, the labeled-release experiment, also initially gave positive results. It was designed to mix a nutrient solution with some soil, and see if there were any metabolic changes. After studying the results, the Viking scientists eventually came to the conclusion that the results were probably due to a chemical reaction. Gilbert Levin, the scientist who designed the experiment, disagreed. He still maintains that it was microorganisms that gave the positive results. He has since published a paper which explains his reasoning, and even claims that some of the other experiments detected life.
Viking also carried a device that would detect organic compounds directly, but it failed to find anything at either landing site. Levin says that the device wasn’t sensitive enough, and the same type of device failed to find organic compounds in Antarctica when all the other experiments would have.
The debate continues over 20 years after Viking. Did the LR experiment detect life? If not, would the experiments have had better luck at a different landing site? Maybe the life on Mars is undetectable by the standard tests — for example, what if it’s not carbon based life? The Viking experiments produced more questions than answers, and most notably did not settle the ultimate question of life on Mars.