Scientists have detected the first possible signs of life forming on another world and gained clues to our own origins. An organic haze surrounding Saturn’s moon Titan is similar to that thought to have helped nourish life on Earth billions of years ago, they said this week.

British experts led the successful landing of an unmanned spaceprobe, Huygens, on Titan in January last year after a 2.5 billion mile journey. It is the only moon with a dense atmosphere and has since been found to have rivers and lakes.

Huygens detected organic chemicals that are the building blocks of life, including nitrogen and methane, as it parachuted to a slushy landing.

Now scientists at Nasa’s Astrobiology Institute have simulated and compared the atmospheres of early Earth and 3,200-mile diameter Titan in the laboratory. Their study appears in the latest Proceedings of the U.S. National Academy of Sciences.

The researchers, led by Melissa Trainer, say their experiments help scientists interpret observations of Titan’s atmosphere from Huygens and its mothership Cassini which is still orbiting Saturn. But it also shows how a major source of organics could have been produced on Earth billions of years ago.

Carl Pilcher, director of the Nasa Astrobiology Institute, at the Ames Research Center, California, said: “It’s exciting to see that the early Earth experiments produced so much organic matter.”

The scientists say that when sunlight hits an atmosphere of methane and nitrogen, like the atmosphere of Titan today, aerosol particles form. When an atmosphere also contains carbon dioxide, as in the atmosphere of ancient Earth, different kinds of particles form. They compare the process to the build-up of city smog.

Chief UK Huygens mission scientist Professor Zarnecki, of the Open University, says air samples taken by the probe are of “great astrobiological interest”. He told me: “We believe the chemistry is there for life to form.”

The photo from Cassini, showing a smog-enshrouded Titan, was taken in February 2005.