Great excitement swept through the scientific community when online astronomy crowdsourcing interface Planet Hunters, using the Kepler telescope, claimed to have found light from a star known as KIC 8462852 was regularly dipping, as if something was blocking it as it travelled to Earth. This got astronomers enthused by the possibility that a more advanced alien civilisation had built a megastructure, such as a Dyson sphere, to harbour energy from said star.

However, after weeks of speculation, boffins at Nasa believe they have finally figured it out, with the reality being predictably duller. The scientists used the space agency's Spitzer Space Telescope, which has infrared capabilities unlike the Kepler telescope, to search for a build-up of dust and rock that glow in infrared temperatures.

"Spitzer has observed all of the hundreds of thousands of stars where Kepler hunted for planets, in the hope of finding infrared emission from circumstellar dust," said Michael Werner, the Spitzer project scientist at Nasa's Jet Propulsion Laboratory in Pasadena, California, and the lead investigator of that particular Spitzer/Kepler observing programme.

They were unable to detect dust and rock through infrared, which left them believing cold comets are responsible for blocking the light from the star. They theorise a family of comets are circling the star, with a very large one leading the pack that would have blocked the light in 2011 – when suspicions were first aroused.

"By the time Spitzer observed the star in 2015, those comets would be farther away, having continued on their long journey around the star. They would not leave any infrared signatures that could be detected," said Nasa in a statement.

"This is a very strange star," said Massimo Marengo of Iowa State University and lead author of the study. "It reminds me of when we first discovered pulsars. They were emitting odd signals nobody had ever seen before, and the first one discovered was named LGM-1 after 'Little Green Men.'"

The LGM-1 signals turned out to be a natural phenomenon. "We may not know yet what's going on around this star," Marengo observed. "But that's what makes it so interesting."