Carl Sagan phoned Gilbert Levin to congratulate him for being the first person in history to discover life on another planet in 1976. For those few days after that call they partied, bought champagne and cigars. But it didn't last. Carl Sagan would quickly withdraw his congratulations...
|The Martian scene where Viking landed in 1976
Gilbert Levin was a NASA scientist who had developed an experiment on the Viking lander called the Labeled Release experiment.
The Labeled Release experiment theory: Get soil sample, add radioactive carbon-14 isotopes to nutrients, mix with the soil. The metabolism of the microorganisms in the soil will release a gas derived from whatever they are feeding on. A Geiger counter can measure the increase in radioactivity. If that works then heat soil sample to 160 degrees Celsius (320 degrees Fahrenheit) this will kill the microbes, but you wont get radioactive gas hence you have killed the life you previously measured.
On the Mars Viking mission, the robot put Martian soil into 4 chambers, about half cubic cm of soil in each. It was then sealed for 24 hours. Nutrients + carbon-14 were added. 15 hours later flat line shot upwards - just like it had happened in pre mission tests in California. They bought champagne, cigars, they had found life on Mars. One chamber was then heated to 160 degrees - it confirmed what they were looking for.
The Labeled Release experiment was one of four experiments looking for life on Mars. The other three were:
Pyrolitic Release - confirmed life - possibly caused by algae.
Gas Exchange - a soup of nutrients mixed with Mars soil, didn't give off any special gasses - indicates that there is no life.
The casting vote was given to the Gas Chromatograph Mass Spectrometer (GCMS) experiment - it tested soil for organic, ie carbon based, compounds. However, it is alleged that this experiment wasn't working properly - it has more recently been claimed by NASA that the experiment was not sensitive enough to measure life in any case. The purpose of the experiment was to roast some soil and then measure it to find carbon based chemicals. The trouble was one of the ovens wasn't working. An indicator showing that a soil sample had been successfully delivered to the second oven didn't work. One of the scientists working on the Viking GCMS experiment told Gilbert Levin, years later, that the results should be treated with caution - the experiment had, it was alleged, failed to find life in a test sample "Antarctic Soil #726". The Labeled Release experiment had found life in "Antarctic Soil #726".
The GCMS experiment showed no carbon organics on Mars. The suggestion was that it was being caused by hydrogen peroxide. 30 years on no hydrogen peroxide has been found.
Possible factors: 1) They could have found extremophile bacteria (found on Earth in places like volcanoes or deep underwater) unknown at the time of the Viking mission.
Postscript: In 1996 NASA held a press conference about the signature of life in a meteorite ALH84001 from Mars. ALH84001 had been on Earth 13,000 years - NASA scientist found what seemed to be fossilized microbes. Wesley Huntress of NASA was asked by journalists whether this meant NASA had changed its mind about life on Mars. They said second Viking lander had landed in desert so no life, said ALH84001 is hint at past life on Mars. It was also said that GCMS experiment was not sensitive enough to rule anything out.
(Source for all above: Chapter 6 - Viking, 13 Things That Don't Make Sense - The most baffling scientific mysteries of our time by Michael Brooks)
Sources: Chapter 6 - Viking, 13 Things That Don't Make Sense - The most baffling scientific mysteries of our time by Michael Brooks
Viking mission to mars: http://nssdc.gsfc.nasa.gov/planetary/viking.html
Wikipedia - Viking experiments http://en.wikipedia.org/wiki/Viking_biological_experiments