Scientists have ruled out the possibility that methane on Mars was brought there by meteorites, implying that it may be generated by life.
Researchers have discovered that methane on Mars is being constantly replenished by an unknown source, and had thought that meteorites might be responsible.
But a new study by researchers from Imperial College London, shows that the volumes of methane that could be released this way are simply too low to maintain the current atmospheric levels. Previous studies have ruled out the possibility that the methane is delivered through volcanic activity.
This leaves only two plausible theories - either there are microorganisms living in the Martian soil that are producing methane gas as a by-product of their metabolic processes, or it's being produced by reactions between volcanic rock and water.
Co-author Professor Mark Sephton, Department of Earth Science and Engineering at Imperial College London, adds: "This work is a big step forward. As Sherlock Holmes said, eliminate all other factors and the one that remains must be the truth. The list of possible sources of methane gas is getting smaller and excitingly, extraterrestrial life still remains an option. Ultimately the final test may have to be on Mars."
The team used a technique called Quantitive Pyrolysis-Fourier Transform Infrared Spectroscopy to reproduce the conditions experienced by meteorites as they enter the Martian atmosphere.
When quantities of gas released by the laboratory experiments were combined with published calculations of meteorite in-fall rates on Mars, the scientists calculated that only 10 kilograms of meteorite methane was produced each year, far below the 100 to 300 tonnes required to replenish methane levels in the Martian atmosphere.
The research appears in Earth and Planetary Science Letters.