The star KIC 8462852 exploded into the public consciousness in October when it was suggested that mysterious signals could be explained by a gigantic artificial structure drifting in front of the star and blocking some of its light.

Astronomer Jason Wright, from Penn State University, told the Atlantic, “Aliens should always be the very last hypothesis you consider, but this looked like something you would expect an alien civilization to build.”



The signals were recorded by the Kepler space telescope in 2011. Kepler monitored 150,000 stars for more than three years. It looked for tiny dips in brightness caused when planets drift in front of their parent star. In the case of KIC 8462852, they got more than they bargained for.

Whereas a giant planet like Jupiter would drop the light by just 1%, KIC 8462852 display two huge dips. Around 800 days into the observation, the star’s light plummeted by 15%. Around the 1,500-day mark, there was a flurry of dimming with one dropping by 20%.

To fall that much, the object passing in front of the star must be almost half the diameter of the star. Yet Jupiter, the largest planet in our solar system, is only one-10th the diameter of the sun. Clearly, there was no way that the mysterious object could be a planet. Hence the speculation about aliens building some kind of gigantic space station.

Faced with such a possibility, astronomers dedicated to the Search for Extraterrestrial Intelligence (SETI) swung into action.

Artificial signals are easily distinguished from natural signals because they can clearly be seen to carry information. Even if you do not know what that information is saying, it is obvious that the wave has been “modulated”.

On six nights between 29 October and 28 November 2015, scientists searched the star for laser pulses using the Boquete optical SETI observatory in Panama. Sensitive to pulses as short as a billionth of a second, they saw nothing out of the ordinary.

“We found no evidence of an advanced civilization beaming intentional laser signals toward Earth,” said Douglas Vakoch, the president of SETI International which led the laser search, in a statement. Vakoch has submitted a paper detailing the observations to the Astrophysical Journal.

Another search of the star, this time using radio waves, also came up empty. The SETI Institute used its Allen Telescope Array to listen in to the star for more than two weeks. They detected no sign of alien signals between 1 and 10 GHz. Although the work does not completely exclude the chance of a radio signal being present, it does significantly reduce the possibility.

“The history of astronomy tells us that every time we thought we had found a phenomenon due to the activities of extraterrestrials, we were wrong,” said SETI Institute astronomer Seth Shostak in a statement. “But although it’s quite likely this star’s strange behaviour is due to nature, not aliens, it’s only prudent to check such things out.”

The most likely natural phenomenon that could block that much light from the star is the collision of comets producing huge clouds of obscuring dust. This explanation was discussed in October but proved less attractive than the alien megastructure idea. Now, however, it may be time to spend time looking more closely at the natural explanation.

“The hypothesis of an alien megastructure around KIC 8462852 is rapidly crumbling apart,” said Vakoch.

Although this is not really a surprise, still there is a bit of me that is disappointed. In hindsight, I suppose a new Star Wars film and the detection of an alien civilisation in the same month would have been too much to hope for.

Stuart Clark is the author of The Unknown Universe (Head of Zeus), and co-host of the podcast The Stuniverse (Bingo Productions). He is teaching the Guardian Masterclass, How the Universe Works in December.