why the wow! signal wasn’t just a rogue comet

Whenever scientists talk about the possibility of detecting alien intelligence, just about every discussion will mention the Wow! Signal, a weird transmission from 1977 we’ve been trying to explain for decades. Of course, there are many things that could pass for alien attempts to get our attention at first blush, especially signals from neutron stars which have been mistaken for extraterrestrial broadcasts not once, but twice because their emissions can be almost as steady as those regulated by computers, or so powerful that they stand out like a primal scream of something very different and unnatural against the steady background noise of space. But the Wow! Signal was very different. It didn’t come from a pulsar, or a satellite, or another planet in our solar system.

It came from a region near a Sun-like star called Tau Sagittarii, roughly 122 light years away, which, again, sounds like more support for the hypothesis that an alien civilization reached out to us and we just happened to be in the right position to catch 72 seconds of it. However, if there were little green or gray men who called its solar system home, they’re either long extinct or moved on by now since the star has already used most of its hydrogen and went through a red giant phase before shrinking back into an orange ball of plasma which will fuse helium until it expands again before finally cooling into a white dwarf.

Basically, that star is us 4.5 billion years from now, which led some experts to propose that we may have eavesdropped on two alien spaceships talking to each other. Unfortunately, that’s an even more improbable scenario requiring not just intelligent alien life, but extremely advanced, spacefaring creatures on deep space missions. Attempts to find other possible points of origin ended up with a list of some 3,000 stars but nothing to narrow down the candidates, especially since the signal was never detected again, leaving us to make the best of the information we already have and nothing more.

slicing through the wow! signal with occam’s razor

So, what could explain this mysterious transmission? According to astronomer Antonio Paris, there’s a clue in the frequency at which it was detected: 1420 MHz, roughly the frequency of hydrogen gas. This means the signal could have some from a comet’s tail, which would contain plenty of hydrogen, leading him to publish a paper claiming that far from being ET phoning long distance, the Wow! Signal was actually comet 266P/Christensen. And at first glance, this would make sense. This comet was not cataloged at the time, was roughly in the same part of the sky as the signal in question, and he was able to detect a similar transmission from tracking and listening to cometary tails with a radio telescope. Furthermore, 266P/Christensen has a variable orbit, making it difficult to catch the signal from it twice.

In a way, this is reminiscent of the questions buzzing around the so-called Tabby Star, which a number of astronomers hinted looks either like it has a massive cometary debris field around it, a megastructure known as a Dyson Sphere, or its variant, a Dyson semaphore. Comets are some of the most abundant objects in the universe, and they collide with each other pretty much all the time, leaving clouds of dust and debris. There’s nothing odd about a field of them orbiting a star. Stellar scale structures build by alien civilizations, however, raise a lot of questions about how they evolved and how they were able to create and maintain their civilization. And since Occam’s Razor dictates that we default to explanations requiring the fewest assumptions, you can see why comet hypotheses for weird astronomical phenomena look attractive.

when extraordinary claims come with extraordinary proof

But according to researchers who tried to follow up on the Wow! Signal, comets simply can’t explain what they saw. First of all, comets wouldn’t create the same kind of signal in only one band to match the exact observation. The signal looked like it was cut off, not fading slowly as the cloud of gas and dust passed over the telescope and was found in a band in which comets aren’t that radio-bright. Secondly, while 266P/Christensen was roughly in the right part of the sky when the signal was detected, it wasn’t at the right place or time to be detected the same way. Finally, the premise that a signal at the frequency of the hydrogen line means a cometary tail could be emitting it is highly questionable considering how far from airtight Paris’ attempt at replicating the signal in question was.

So, does all this mean we’ve definitely heard an alien broadcast in 1977? Not exactly. As noted, there are perfectly natural phenomena which can seem very artificial when first detected and the Wow! Signal may be an example of that. While we don’t know exactly what could’ve caused it, so far all we’ve been able to do is rule out almost every otherwise possible culprit, which is both frustrating and exciting because it means we really don’t understand what we saw, and any claims otherwise are premature at best. Based on what we know today, the signal is bound to remain a mystery for a long time to come and may never be fully replicated or explained to the satisfaction of everyone involved in the research. But that’s just how the universe works. It really doesn’t care if your questions are ever answered.