Not everyone agrees that Titan is the priority, though. NASA and ESA recently gave the nod to a Jupiter-system mission that will explore Europa as the next flagship mission to the outer solar system. It may be decades before another major mission flies to Saturn and Titan.

But a smaller-scale and less-expensive lander known as the Titan Mare Explorer (TiME) could launch as early as 2015, arriving in 2022 or 2023. Ellen Stofan of Proxemy Research in Rectortown, Va., the principal investigator for the TiME mission, described the lander as a buoy-shaped capsule that would splash down in one of Titan’s northern lakes and float across its surface for a minimum of two Titan days (sixteen Earth days).

“We have a number of instruments on board. The most important from a pure scientific point of view is a mass spectrometer,” Stofan said. “We’ll take basically a sip of [the lake] liquids, several times, and analyze them to really nail down their chemical compositions. We know there’s methane, we know there’s ethane,” but TiME would inventory more complex organic (hydrocarbon) compounds, as well.

If there is life on Titan, it may be difficult to detect. “I don’t expect you to go to these lakes and see beautiful filamentary structures made of cells that are macroscopic in size or easily seen,” says Lunine, who is a co-investigator on the proposed TiME mission. The clues could be subtle. “We would have to look for particular peculiarities in composition, hydrocarbons that are lacking that should be there, others that are more abundant” than expected.

No-one knows “what happens to organic chemistry in [Titan’s] environment,” Lunine adds. “Does it go to a kind of a chemistry that we can call life but works in liquid hydrocarbons? We don’t know the answer to that. But the answer is profound.” Because if the answer is yes, it means that the origin of life has taken place more than once. “If the answer is yes, then it says that life … must be a common outcome of planetary processes in the cosmos.”

If the answer is yes, it means we are not alone.

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