Worlds with fluent water is the standard definition for a world that could harbor life.

And yet many scientists now believe life may have found a way to take hold on Titan, with its methane-lakes.

“What Cassini actually found on Titan, from 2004 onwards, was a methane-ethane cycle that very much echoes the kind of hydrologic cycle we see on the Earth” says Jonathan Lunine, currently a NASA investigator from University of Rome Tor Vergata.

Methane is the simplest hydrocarbon molecule. By themselves, they are of limited biological interest. But hydrocarbons are versatile: they can assemble themselves into fantastically complex structures.

And then there is the temperature, since Tian is -100 degrees C “We don’t have a lot of experience with the chemistry that might go on at these temperatures.”  Lunine says

If there is life on Titan, it is not life as we know it. Lunine continues: “DNA and RNA form out of compounds that require oxygen and phosphorus, and there’s very little oxygen in the Titan system.DNA forms a helix because of its water-loving and water-repellant ends.So life on Titan would have to find other molecules that carry information.”

Terrestrial life could not have originated from Titan, and neither would life from Earth (eg. contaminations from landers, or meteorites) could not have survived on Titan, so if we find life, it has nothing to do with life on Earth.

"What happens to organic chemistry in this environment. 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.If the answer is yes, then it says that life … must be a common outcome of planetary processes in the cosmos.”

This is why NASA is investigating a probe to go to Titan and actually land in one of it's lakes. This is also the mission that Lunine is investigating for NASA.

If nothing (budgets mainly) goes wrong, the Titan Mare lander should be launched in 2016 and reach Titan in 2022.

Read more on NASA's astrobio magazine