Scientists may never know for sure if NASA's Curiosity rover detected signs of life on Mars two years ago, but now is the right time for them to gather some promising clues.
Last December, the Curiosity team announced that methane concentrations in the air around the rover, which has been exploring Mars' 96-mile-wide (154 kilometers) Gale Crater since August 2012, jumped by a factor of 10 for about two months from late 2013 through early 2014.
Here on Earth, the vast majority of atmospheric methane has a biological origin, so news of Curiosity's discovery made a big splash among both scientists and the general public. [Inside Curiosity's Mars Methane Discovery (Infographic)]
But Red Planet microbes aren't the only possible explanation; geological processes can produce methane as well. Indeed, a new study lays out three scenarios that could explain the mysterious spike, and only one of them invokes the presence of Mars life.