There’s yet another nail in the coffin of everyone’s favorite alien megastructure. A new study by NASA’s Spitzer Space Telescope suggests that the mystery object spotted around the distant star KIC 8462852 is a swarm of comets, rather than an extraterrestrial structure.

The study, led by Massimo Marengo of Iowa State University and to be published in the Astrophysical Journal Letters, examined the infrared light from the star. An unusually large amount of such light would indicate that a planetary impact or asteroid collision caused the large object seen blocking the star’s light – and, although not mentioned by the paper, infrared light would also be an indication of the proposed alien megastructure.

But Spitzer didn’t find any such infrared excess. According to the researchers, this favors the idea that a swarm of cold comets first blocked out the star’s light in 2011. In 2013, cometary fragments lagging behind the main group then blocked its light again. By 2015, though, this swarm had passed out of our line of sight.

Aside from the rather fanciful alien theory, the result is disappointing for scientists hoping to see evidence of astronomical dust around stars. "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, in a statement.

^{The dip in light first spotted by Kepler is probably a swarm of comets. Diego Barucco/Shutterstock}

This star, 1,400 light-years away, grabbed headlines in October when Jason Wright, an astrophysicist from Pennsylvania State University, suggested to The Atlantic that a huge dip in light seen from the star – up to 20 percent of its light – could be artificial in origin. This had people dreaming of Dyson spheres, vast theoretical structures that could potentially harness the power of entire stars, and other exciting extraterrestrial constructs.

But following this suggestion, the SETI (Search for Extraterrestrial Intelligence) Institute in Mountain View, California, trained their vast Allen Telescope Array of 42 antennas on the system. It failed to find any signals that could be artificial in origin, pouring cold water on the “alien megastructure” theory.

The case is far from closed, but for now it’s looking likely that a natural phenomenon, namely a swarm of comets or cometary fragments, is the cause – as originally postulated by the author of the paper first describing the star, Tabetha Boyajian, in September.

"We may not know yet what's going on around this star," said Marengo in the statement. "But that's what makes it so interesting."