As greenhouse gases go, carbon dioxide might get all the attention, but methane is the quiet powerhouse. While it isn't as prevalent as carbon dioxide, the EPA estimates that methane is 25 times more potent than its more famous fellow emission, able to trap more heat in the atmosphere.
Ah, the oxygen-rich surface of the ocean, where the air and water meet, and life flourishes. But you might not know that these waters are also supersaturated with methane relative to the atmosphere, a phenomenon termed the "marine methane paradox." The question being: Where does this methane come from? The answer matters because this methane eventually makes its way into the atmosphere, where it readily traps heat, giving it a 20-fold greater impact on climate change than carbon dioxide, pound for pound.
Finding methane on another world is like finding breadcrumbs on a trail - it's a telling clue, a detail that gives reason to ask more questions and maybe find some answers, in this case related to extraterrestrial life. This is why news from the Mars rover Curiosity late last week is kind of disappointing - looking around for methane, Curiosity found a whole lot of nothing.