Evidence that life exists on Titan, one of Saturn's biggest moons, appears to have been uncovered by Nasa scientists.

Researchers at the space agency believe they have discovered vital clues that appeared to indicate that aliens could be living on the moon.

Data from Nasa's Cassini probe has analysed the complex chemistry on the surface of Titan, which experts say is the only moon around the planet to have a atmosphere.

They suggest that life forms may have been breathing in the planet's atmosphere and also feeding on its surface's fuel.

Astronomers claim the moon is generally too cold to support even liquid water on its surface.

The first paper, in the journal Icarus, shows that gas flowing throughout the planet's atmosphere disappeared at the surface. This suggested that alien forms could in fact breathe.

The second paper, in the Journal of Geophysical Research, concluded that there was lack of the chemical on the surface.

Scientists were then led to believe it had been possibly consumed by life.

Researchers had expected sunlight interacting with chemicals in the atmosphere to produce gas. But the Cassini did not detect any such gas.

Chris McKay, an astrobiologist at Nasa Ames Research Centre, at Moffett Field, California who led the research, said: “We suggested hydrogen consumption because it's the obvious gas for life to consume on Titan, similar to the way we consume oxygen on Earth.

"If these signs do turn out to be a sign of life, it would be doubly exciting because it would represent a second form of life independent from water-based life on Earth."

Professor John Zarnecki, of the Open University, added: "We believe the chemistry is there for life to form. It just needs heat and warmth to kick-start the process."

"In four billion years' time, when the Sun swells into a red giant, it could be paradise on Titan."

They warned, however, that there could be other explanations for the findings.

But taken together, they two indicate two important conditions necessary for -based life to exist.