No Martian Methane
In 2009, Earth-based researchers announced that they might have detected large plumes of methane on Mars. The findings raised some eyebrows, mainly because they seemed too good to be true but also because of what they implied. Methane is a simple organic compound that is almost entirely a byproduct of living organisms on Earth. Nearly 99 percent of methane on our planet comes from microbial action and cow farts, and seeing it on Mars raised the hopes of those who think life may still exist on the Red Planet.
Alas, Curiosity has sniffed the Martian atmosphere and turned up methane-free. Though it found certain molecular clues that show Mars would have once had a thicker atmosphere and therefore have been warmer, it has all but crushed the optimistic expectations for finding modern microbes on Mars. But hope remains. The methane on Mars may simply be seasonal, released when the climate is more temperate or other factors are present. Curiosity will continue to periodically test the atmosphere to search for this elusive gas and may one day find something exciting.
Image: Curiosity's Sample Analysis at Mars (SAM) instrument, which analyzed the Martian atmosphere. NASA/JPL-Caltech/MSSS