Mr Plowman is writing a book on the subject that is due out in November. First-hand experience of UFOs has eluded him and he maintains a healthy scepticism about their existence. Often people have mistaken comets, aircraft or birds for UFOs, he said, but "when I meet someone who says they've seen something strange, that's fair enough because maybe they have. I don't know what it is, though". Someone he met in Melbourne claimed to have been kidnapped by Martians. "They seem like something has happened to them," Mr Plowman said. "The first time you meet an abductee as they are called, it can be quite confronting because they are trying to come to terms with it … it is something that can stay with people a long time."

The last abduction claim in Melbourne was 15 years ago; Kelly Cahill claimed to have flashbacks of being taken by strange creatures at Narre Warren, Mr Plowman said. His research into UFOs took him to places associated with sightings: Roswell, New Mexico, where it is claimed that a flying saucer crashed in 1947; Wiltshire, England, where crop circles have been attributed to spaceships, and Latin America, the latest source of reported sightings "where they are working it into their own indigenous belief systems.

"In the Andes, in Chile, they showed me a rock where they claimed an alien had stepped and left a footprint in the rock." Mr Plowman's interest in UFOs arose out of boredom. As a child, he spent time in hospital and his parents bought him a book on UFOs to distract him. "It captured my imagination," he said. His interest waned and he went on to study physics. But that interest was reignited when he noticed books on UFOs at a fellow physics student's house. "Having a look at [them], I realised this was a whole world unto itself," he said. "It had rules and ideas and history, and it hadn't been looked at much, so my enthusiasm came back and I thought this is a story that I want to look at."