A new theory suggests that the origin of a famously unexplained signal from space recorded nearly 39 years ago may have been caused by two passing comets.

In 1977, a volunteer radio astronomer named Jerry Ehman was studying data collected by the Big Ear telescope at Ohio State University when he noticed a signal 30 times stronger than any of the normal radio waves detected. Ehman circled some of the characters on a printout that represented the abnormal 72-second-long signal, and next to them he wrote the word "Wow!" which was later adopted as the name of the rare discovery. The signal was never found again. Nevertheless, for decades some have believed that the Wow! signal was our planet's first interception of an alien broadcast.

According to a new theory by St. Petersburg College astronomer Antonio Paris, soon be published in the Journal of the Washington Academy of Sciences, hydrogen clouds from two comets that were not known at the time—266P/Christensen and P/2008 Y2 (Gibbs)—could be responsible. "I came across the idea when I was in my car driving and wondered if a planetary body, moving fast enough, could be the source," Paris told New Scientist.

The magazine reports that as comets orbit around the Sun, they release clouds of hydrogen because "ultraviolet light breaks up their frozen water, creating a cloud of the gas extending millions of kilometres out from the comet itself." And not everyone is convinced the comets would release enough hydrogen to generate the signal, New Scientist notes. Paris suggests testing his theory by studying the comets when they return to the region on January 25, 2017 and January 7, 2018, respectively.

[h/t IFL Science]