Lesson 6: Search for Life in Our Solar System

A Close Study of Mars

In 1976, NASA’s Viking Landers detected methane in an incubated soil sample on Mars which was a major discovery for scientists. Since atmospheric methane on Earth is derived from biotic sources, it is natural to assume that methane is a significant biosignature gas to indicate some form of life on Mars. Many hypotheses have been put forward to account for the methane production on Mars, with biotic life a possible scenario. Research groups have studied deserts on Earth in order to better understand if life in these arid environments could release methane gas. Anaerobic decomposition of organic material is a source of methane gas and was observed in soil samples in deserts in Utah which supports the hypothesis of biological life on Mars in the soil. Coupled with the discovery of ice on Mars, some form of life is plausible.

However, Methane is also produced by geological sources, such as volcanoes, which is a non-biological source. Volcanic methane is usually accompanied by a release of sulfur dioxide which is not present in the Martian atmosphere, suggesting that this is not a possible scenario for methane production on Mars. Methane is an unstable gas and if levels are constant in the atmosphere of a planet, this suggests that there is a life form that consistently produces it. These methane peaks were found to occur every 24.66 hours (which is one Martian “day”) which can indicate that there is some form of life that exists in a circadian rhythm.

NASA’s Curiosity Rover has since been sent to Mars and did not detect methane in early 2013 which discounted the results of the Viking mission. However, in late 2013 and early 2014, it did detect a peak in methane levels in the surrounding air which suggested that any possible life on Mars may undergo a yearly cycle as Earth does. These results have been repeatedly analysed and new missions are planned for Mars to redetect methane peaks in the atmosphere.

Currently, it is unknown whether biotic or abiotic processes produce the methane found in the Martian atmosphere but many studies conclude that from this evidence, life on Mars is “likely present and active”.