Imperial College London scientists say they have ruled out the possibility that methane is delivered by meteorites into Mars' atmosphere.
That finding, the researchers note, raises fresh hopes that the gas might be generated by life on the red planet.
Scientists said methane on Mars is being constantly replenished by an unidentified source. Researchers had thought meteorites might be responsible because, when the rocks enter the planet's atmosphere, they're subjected to intense heat, causing a chemical reaction that releases methane and other gases into the atmosphere.
But now the Imperial College London study has shown the volumes of such meteoritic methane are too low to maintain the current atmospheric levels of methane. Previous studies have also ruled out the possibility the methane is created through volcanic activity.
That, the researchers say, means either there are microorganisms living in the martian soil producing methane gas or methane is being produced as a by-product of reactions between volcanic rock and water.
Professor Mark Sephton, a co-author of the study, noted: "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 research appears in the journal Earth and Planetary Science Letters.
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