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‘Alien Megastructure’ Is Probably Just a Swarm of Comets, Researchers Say

Iowa State university astronomers explain what likely happened with star KIC 8462852.
November 30, 2015, 11:00am

A group of astronomers from Iowa State Univeristy think they have solved a recent cosmic mystery: the strange fluctuations in light coming from star KIC 8462852, a distant sun nestled between the constellations Cygnus and Lyra, which some scientists had guessed might be a sign of an "alien megastructure."

The new research study published in the Astrophysical Journal Letters indicates the likely culprit is not an alien construction site, unfortunately, but rather a swarm of comets.


Led by Massimo Marengo, associate professor of physics and astronomy at Iowa State, the research expands on the original stellar discovery made by Yale Postdoc Tabitha Boyajian.

"After further observations, it appears that the scenario in which the dimming in the KIC 8462852 light curve were caused by the destruction of a family of comets remains the preferred explanation," the paper says.

NASA's Kepler Space Telescope has monitored a patch of sky for four years in search of exoplanets, or planets beyond our Solar System. On two separate occasions, once in 2011 and again in 2013, astronomers noticed something odd around the star KIC 8462852.

Kepler is trained to look for dips in starlight, which signal to astronomers that a planet is passing between the star and the telescope, thus blocking out some of the light. Based on how big the dip is, astronomers can tell what size planet is crossing in front of the star. Planets orbit their host star in regular intervals, with predictable dips in starlight. However, Kepler found KIC 8462852 to be a completely different story.

Just to recap: We have not detected any sort of alien radio signals, and astronomers have ruled out smashed up bits of planets or asteroids

Kepler observed that as much as 20 percent of KIC 8462852's starlight was blocked out, something the telescope had never spotted before. The dip was too much for a planet, so there had to be another explanation. Some scientists postulated it could be a family of comets, asteroids, or debris from a smashed up planet. There were even some scientists who believed it could be a massive alien-made structure. The Search for Extraterrestrial Intelligence Institute (SETI) observed the star in hopes of detecting alien radio signals, but came up empty handed.

Since Kepler can only see visible light, astronomers turned to a duo of infrared telescopes In order to help determine what was causing the weird stellar fluctuations. The two infrared telescopes—NASA's Spitzer Space Telescope and NASA's Wide-Field Infrared Survey Explorer (WISE)—scanned the same patch of sky as Kepler looking for signs of comets or other planetary bodies around KIC 8462852. Dusty debris leftover from planetary collisions shines in the infrared and can easily be spotted by Spitzer and WISE.


If the light fluctuations were caused by some sort of planetary impacts or asteroid collision, there would be an excess of infrared light and dusty debris shining in the infrared. The team analyzed WISE data collected in 2010, prior to the first event. They searched for any signs of dust and debris and could not find any. So the team turned to Spitzer.

Spitzer observed the same patch of sky as Kepler and WISE, looking for evidence of any dust and debris kicked up after the bizarre events. Just like WISE, Spitzer saw no signs of warm dust or an excess of infrared light, indicating that any sort of collision was out of the question.

Just to recap: We have not detected any sort of alien radio signals, and astronomers have ruled out smashed up bits of planets or asteroids. So what is causing these bizarre stellar fluctuations? Comets. A lot of them.

Most of the comets we see in our Solar System are lone icy bodies whizzing around the Sun. However, it is possible for comets to travel in packs, and that's what the evidence shows is happening with KIC 8452852. In this case, one very large comet probably led the pack, which explains the 2011 dip. Following behind would be a family of smaller comets, which caused the 2013 blackout.

When Spitzer turned its eye to the star earlier this year, the cometary horde would have already reached perihelion (closest point to its host star) and be headed away from the star on a very eccentric orbit. Comets are icy bodies and as such would not have left any infrared signature behind for Spitzer to detect.

"KIC 8462852 is a cosmic mystery. We may not know yet what is going on with this star, but that's what makes it so interesting," the researchers wrote. "More observations are needed to solve this riddle."