During a follow-up test over the weekend, though, scientists found that the methane levels around the rover already dropped sharply. Curiosity detected normal methane levels (1 part per billion by volume) following the sudden elevation, suggesting that the abnormally high values came from transient methane plumes. So, what does that mean? Well, Paul Mahaffy, the principal investigator for Curiosity's Sample Analysis at Mars instrument, said during a townhall event: "A plume came and a plume went."

Curiosity unfortunately doesn't have the instruments to determine whether the source of methane is biological or geological. Further, scientists have yet to figure out a pattern for Martian's transient plumes. In other words, they're still nowhere close to unraveling the planet's methane mystery. They need to gather more information through Curiosity and from other missions to gain a deeper understanding of the plumes. When they finally understand where the plumes are coming from, maybe then they can figure out whether the presence of methane on the red planet truly is a sign of life.

Ashwin Vasavada, Curiosity project scientist at NASA's JPL, said: