The Viking biology experiments on Mars revisited

The discovery of perchlorate on Mars by the Phoenix mission has provided a basis for explaining the results of the Viking Landers. Thermal decomposition of perchlorate in the ovens of the instrument can explain the lack of organics detected. Accumulation of hypochlorite in the soil from cosmic ray decomposition of perchlorate can explain the reactivity seen when nutrient solutions were added to the soil in the Viking Biology Experiments. A non-biological explanation for the Viking results does not preclude life on Mars. • We have reconsidered the results of the Viking Biology Experiments. • The most significant change since these experiments were conducted was the discovery of high levels of perchlorate on Mars. • Perchlorate, plus abiotic oxidants, explains the Viking results and there is no requirement to postulate life on Mars.