Ever since Curiosity landed on Mars, it has been in search of methane. It couldn't find any for years, until a new set of experiments unveiled today that detected large spikes in methane. Scientists have no idea what caused the spikes, but the most intriguing explanation is "life on Mars."

Much of the methane on Earth comes from microbes belching the gas into the atmosphere. NASA scientists caution there are still non-biological explanations for methane on Mars, such as ultraviolet radiation causing chemical reactions on Mars's surface or trapped methane being released from lattices of ice.

Finding methane was not easy for Curiosity and its scientists. Although other missions have found trace amounts of methane in the Martian atmosphere before, Curiosity had been unable to detect the gas because—as we now know—background levels were just a bit too low for the rover's instruments. Instead, as Lee Billings at Scientific American explains, Curiosity had to strip carbon dioxide out of its gas samples to enhance the small amounts of background methane.

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As the rover traveled across Mars over two months, its instruments also found four transient spikes in methane, about ten times the background level. These spikes suggest a source, but a still mysterious one at that. To get to the bottom of these bursts of methane, we may have to wait for the next Martian rover in 2020. [NASA, Scientific American]