Imagine you're an astronomer listening into outer space for something as quiet as a pin dropping, when suddenly you hear something as loud as a fog horn.
That's what happened to an Ohio astronomer at SETI in 1977 listening to space with a radio telescope.
The sound was so strong and surprising that Jerry Ehman wrote "wow" right on the chart, and since then, the sound he heard has been known as the "Wow! signal."
Now, a scientist at the Museum of Science and Industry thinks he's solved the mystery of what caused the sound.
"With the use of radio telescopes we can sit there and record all these cool sounds," explains Professor Antonio Paris, the President of Space Programs at MOSI.
"Some of them sound like sonar pings from a submarine, some sound like spooky sounds like from a haunted house," says Paris, who thinks some scientists have been distracted by less plausible explanations for the radio noise.
"Because everyone was looking for aliens!" says Paris, referring to a strongly-held belief by some that the noise is the strongest clue yet that life exists elsewhere. "For the most part everyone is looking for a radio signal from an extra terrestrial source, and I wanted to approach this from a natural phenomena."
Meanwhile, he says, the scientific community has learned a lot more about space, especially the paths of comets only recently discovered, which leads Paris to his theory.
"Basically what we found was two comets that were in the very same area during the same time and same date," when the "Wow! signal" was recorded. "Astronomically speaking when you look at the universe for these things to all be in the same place its one in a billion," says Paris.
That's why he thinks there's enough evidence to suggest those comets, recently discovered by NASA, caused the "Wow! signal."
His theory was just published with The Center For Planetary Science for other astronomers to study as well.
