First there was evidence of fossil bacteria in a Martian rock found in Antarctica. Next came confirmation of liquid water on the surface of Mars in the distant past. Now three separate scientific teams have discovered methane in the Martian atmosphere. On Earth, two primary sources produce methane: volcanoes and life.
So, what is the source of that methane on Mars? First, scientists needs to confirm that the methane actually exists there and is not an error in their research. Next, differences in methane concentration need to be mapped and correlated with possible Martian sources. Finally, robots and/or humans need to explore the potential sources up close. I volunteer.