One month ago marked the 50th anniversary of the first, and so far last, direct Martian life detection experiments. Two Viking rovers were sent to different locations, where each performed the same four experiments.
- Organics in soil. A gas chromatography/mass spectrometer experiment scanned for organic compounds released when a soil sample was heated. None were found. Hold that thought.
- The labeled release experiment incubated soil with nutrients having a portion of the usual carbon-12 atoms replaced with carbon-14, which is radioactive and therefore more easily detected. Both landers logged an immediate release of labeled carbon dioxide from cold samples, but not from prebaked (presumably sterilized) samples.
- The gas exchange experiment incubated soil with water and nutrients to see whether gases around the sample changed. Both landers observed immediate oxygen release. While this is interesting, the response did not resemble ordinary terrestrial biology and gradually weakened as the observation continued. This might be explained by soil chemistry rather than the presence of life.
- The pyrolytic release experiment exposed Martian soil to radioactive carbon monoxide and carbon dioxide under artificial sunlight. Samples were then heated to see whether radioactive organic compounds were produced. Results were weak and inconclusive.
The official conclusion? Viking could not have detected signs of life on Mars, because if there were life, the GC/MS would have detected organic compounds in the soil. Mars is dead, Q.E.D.
The fly in that ointment is that no one suspected in 1976 that Martian soil contains perchlorates, which are stable when cold but decompose when heated, releasing chemicals that oxidize organic compounds. Two later rovers, neither designed to test for Martian life, found that fly—in 2008, the Phoenix rover detected perchlorates at a level of half a percent, in Martian arctic soil. Later, Curiosity detected numerous organic compounds in multiple locations. Using a derivatization technique on material drilled in 2020, Curiosity identified 21 carbon-containing compounds, including seven never before detected on Mars, such as:
- aromatic compounds
- nitrogen-bearing organics
- sulfur-bearing organics
- oxygen-bearing organics
- ester- and carboxylic acid-containing molecules
- benzothiophene and related aromatic sulfur compounds
So this demonstrates that organic compounds are widely distributed on Mars. It also shows that perchlorates probably oxidized any organic compounds in the Viking samples, and might have been responsible for the detection of chloromethane and dichloromethane, originally suspected to be contaminants brought from Earth.
Does this mean the Viking experiments were ill-designed? It does not! That was the best we could do with the knowledge and equipment available at the time. Does it mean Viking found evidence of Martian life in 1976? No. But it does mean that the consensus opinion that Viking could not have found evidence of life was drastically mistaken. And it also shows that if you keep an open mind, brilliant new ideas might drop in.
Kevin Kelly, July 31, 2026