Methane on Mars: what does it mean?

NASA's Curiosity Rover has detected the highest ever levels of methane in the course of its mission on Mars, an exciting discovery because the gas could point to the existence of microbial life.

Curiosity's Sample Analysis at Mars (SAM) tunable laser spectrometer detected the reading -- 21 parts per billion units by volume (ppbv).

The Curiosity team has caught whiffs of methane many times over since Curiosity touched down on the Martian surface in 2012. One leading theory is that the methane is being released from underground reservoirs created by ancient life forms.