EVIDENCE of life has been discovered on Saturn's biggest moon, Titan.

Analysis of data sent back by NASA's Cassini probe suggests primitive aliens are breathing in Titan's atmosphere and feeding on fuel at the surface.

The startling discoveries, made using an orbiting spacecraft, are revealed in two separate reports.

Organic chemicals had already been detected on Titan but the liquid is methane, not water, and scientists expect life there to be methane-based.

The first paper said hydrogen gas flowing down through Titan's atmosphere disappears at the surface, suggesting it could be being breathed by alien bugs.

The other paper reports there is a lack of a certain chemical on the surface, leading scientists to believe it may be being consumed by life.

Scientists had expected sunlight interacting with chemicals in the atmosphere to produce a coating of acetylene on Titan's surface but Cassini detected no acetylene there.

Experts warn there could be other explanations for the results. But taken together, they fulfil two important conditions necessary for methane-based life to exist.

NASA astrobiologist Chris McKay said: "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."

Scientists believe that when the Sun swells up, swallowing Earth, conditions could be ideal on Titan.

Professor John Zarnecki, of the Open University, said: "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."