Alien Megastructure? Probably Not. Exocomets More Likely

Alien Megastructure? Probably Not. Exocomets More Likely – Alien megastructure, we hardly knew ye. After a star’s bizarre appearance sparked news reports earlier this month about extraterrestrial intelligence, a new study suggests it was lowly comet fragments causing the bizarre dimming and brightening spotted by the Kepler space telescope in 2011 and 2013.

The news comes as not that big of a surprise, given that astronomers were already considering comets as an explanation — and that SETI tried pointing a radio antenna at the star and found no signals. But the new study adds that the early data from the Spitzer Space Telescope will need more follow-up to figure out the full story of KIC 8462852′s situation.

Kepler scans stars to look for signs of planets passing in front of them, which causes the stars’ light to dim. But KIC 8462852 had an irregular pattern of brightening and dimming that puzzled astronomers, leading to speculation it was fragments of material from comets, asteroids or planets. Also, some observers in the media said it could be a large alien structure causing the pattern.

Spitzer came in handy because it looks at the universe in infrared light. It’s the perfect set of wavelengths to observe a planet or asteroid because dust glows in infrared. The research team at first used data from NASA’s Wide-Field Infrared Survey Explorer, but the 2010 observations showed little — perhaps because they were done before the Kepler space telescope saw the bizarre signal.

Luckily, Spitzer happened to look at the star this year as part of the normal follow-up procedure for Kepler observations; Spitzer usually looks for dust from planet fragments. Like WISE, the more sensitive Spitzer also saw nothing in infrared wavelengths, so the objects are likely not leaking warm dust from a planetary or asteroid-scale collision. Cold comets, however? A strong possibility.

“It’s possible that a family of comets is traveling on a very long, eccentric orbit around the star,” NASA wrote in a press release about the study. “At the head of the pack would be a very large comet, which would have blocked the star’s light in 2011, as noted by Kepler. Later, in 2013, the rest of the comet family, a band of varied fragments lagging behind, would have passed in front of the star and again blocked its light.”

The study is led by Massimo Marengo of Iowa State University, and is accepted for publication in the Astrophysical Journal Letters. You can view the preprint version on Arxiv.