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Comet storm, not alien megastructures
This illustration shows a star behind a shattered comet. Observations of the star KIC 8462852 by NASA’s Kepler and Spitzer space telescopes suggest that its unusual light signals are probably due to dusty comet fragments that blocked the light of the star. (Credit: NASA / JPL-Caltech)

Recent infrared observations of a star that once showed a pattern of weird dimming have turned up no anomalous readings, astronomers say – and that supports the view that a comet blitz rather than the construction of an alien megastructure was behind the earlier observations.

The latest evidence, laid out in a paper published in the Astrophysical Journal Letters, isn’t exactly surprising. The passing of a shattered comet was seen as the leading orthodox explanation for the star KIC 8462852’s strange behavior.

But there was also the unorthodox explanation. The readings from the star, gathered by NASA’s Kepler space telescope and analyzed by a citizen-science project known as the Planet Hunters, created a stir because of a potential alien connection.

The starlight from KIC 8462852 dimmed dramatically – by as much as 22 percent – on an erratic schedule during the 2011-2013 time frame. Last month, Penn State astronomer Jason Wright said that pattern matched what might be expected if an advanced extraterrestrial civilization were to start building an enormous energy-harvesting structure around a star. Such structures, known as Dyson spheres, have been the subject of speculation for decades.

The speculation rose to the point that the SETI Institute kept watch on KIC 8462852, which is about 1,500 light-years away in the constellation Cygnus. Nothing unusual was detected.

Astronomers from Iowa State University didn’t see anything unusual, either, when they analyzed infrared readings from the star that were collected by NASA’s Spitzer Space Telescope this January. They saw no strong evidence of the dust or debris that should have been left behind by an asteroid pile-up or the catastrophic breakup of a celestial body (or, for that matter, a wrecked Dyson sphere).

“The scenario in which the dimming[s] in the KIC 8462852 light curve were caused by the destruction of a family of comets remains the preferred explanation for the undetectable amount of infrared excess associated with the Kepler events,” the team of astronomers, led by Professor Massimo Marengo, write in their research paper.

Comet fragments coming in rapidly on steep trajectories could have created a series of huge debris clouds that caused the starlight to dim erratically. Such clouds would move off quickly, restoring the star’s brightness and leaving no trace of excess infrared emissions.

Case closed? Not necessarily. The comet hypothesis isn’t based as much on direct evidence as it is on the absence of evidence for alternate hypotheses. There’s still a chance that a previously unknown phenomenon caused KIC 8462852’s weird winking (although alien megastructures are now even farther down the list of possibilities).

“It reminds me of when we first discovered pulsars,” Marengo said in a NASA news release. “They were emitting odd signals nobody had ever seen before, and the first one discovered was named LGM-1 after ‘Little Green Men.'”

Astronomers eventually figured out that rotating, radio-emitting neutron stars were creating the LGM-1 signal and lots of similar signals that were observed elsewhere subsequently. The same scenario may well play out with KIC 8462852.

“We may not know yet what’s going on around this star,” Marengo observed. “But that’s what makes it so interesting.”

In addition to Marengo, the authors of “KIC 8462852: The Infrared Flux” include Alan Hulsebus and Sarah Willis.

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