Larger than the planet Mercury, and with an atmosphere denser than the Earth’s, Saturn’s moon Titan is only the second-largest moon in the solar system, but definitely the most unusual.

Unique among all other moons in the solar system, Titan possesses an atmosphere, one that is sufficiently thick enough for clouds to form, in addition to wind and rain. Deeper probing by NASA’s Huygens probe revealed the presence of huge lakes, rivers and seas covering the moon’s surface. Of course, the weather is rather more alien than what we experience on EarthTitan’s atmosphere is mostly composed of a mix of nitrogen and methane, rather than oxygen. As a result, Titan’s rain and its great oceans are almost pure liquid methane.

The presence of liquid on Titan’s surface, coupled with a protective atmosphere, raised some interest in regards to the possibility of life emerging there. But such questions run afoul of one of the biggest uncertainties in the search for alien life: is oxygen and water an essential component of life, or is it possible for life to thrive on other chemicals, instead? Could a life form emerge that breathes the nitrogen air as freely as our oxygen, and to whom liquid methane is as life-giving as water?

Some scientists believe it is possible. A team from Cornell University has recently revealed a hypothetical model of a cell structure that is formed out of nitrogen, carbon and hydrogen, wrapped in a methane shell. All these elements are present in Titan’s atmosphere. The researchers expressed some surprise at their successful working model: ‘We didn’t come in with any preconceptions about what should be in a membrane and what shouldn’t,” said Paulette Clancy, a chemical molecular dynamics expert on the Cornell team. “We just worked with the compounds that we knew were there and asked, ‘If this was your palette, what can you make out of that?’”

Furthermore, analysis of the atmosphere conducted by NASA’s Cassini probe has revealed the presence of hydrogen cyanide in Titan’s atmosphere, which some scientists believe adds extra weight to the possibility of life. This is because hydrogen cyanide can react to form complex polymers such as polyimide, a complex and adaptive molecule which is essential for the formation of life. ‘‘Polyimine can exist as different structures, and they may be able to accomplish remarkable things at low temperatures, especially under Titan’s conditions’’, said chemist Martin Rahm from Cornell University. Simulations run by Rahm and his team demonstrated how polyamine could react in Titan’s frigid temperatures to give way to life – at least, in theory. ‘‘Prerequisites for processes leading to a different kind of life could exist on Titan, but this is only the first step’’, Rahm said.

There are, of course, some major obstacles. The temperatures on Titan are generally in the range of -172 C and Titan only receives about 1% of the light the Earth does. But certain organisms on Earth can and do survive in extreme colds and total darkness. Although life on Titan, should it exist, is unlikely to be particularly advanced or complex, confirmation of life existing outside Earth would radically alter mankind’s perception of the outer universe. If life can emerge twice in the same solar system, then one would assume that the rest of the galaxy is similarly teeming with life.

– Greg Taylor, Correspondent (Science)