Scientists at US space agency NASA have found vital clues that primitive aliens could be living on Titan, one of Saturn's biggest moons.
On the basis of chemical composition found on Titan's surface, the experts believe that life forms have been breathing in the planet's atmosphere and also feeding on its surface's fuel.
The research based on the analysis of data sent from NASA's Cassini probe has been detailed in two separate studies.
The first paper, in the journal Icarus, shows that hydrogen gas flowing throughout the planet's atmosphere disappeared at the surface. This suggested that alien forms could breathe.
The second paper, in the Journal of Geophysical Research, concluded that there was lack of chemical on the surface as it had been possibly consumed by the living aliens, The Telegraph reported.
"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," said Chris McKay, astrobiologist at NASA Ames Research Centre, at Moffett Field, California, who led the research.
"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, 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."
They warned, however, that there could be other explanations for the findings. But taken together, they two indicate two important conditions necessary for methane-based life to exist.