On Astronomical Accidents, and the Proxima Centauri ‘Signal’ that Wasn’t

One night a few years back I had a late night call from a friend who was involved in Breakthrough Starshot, the attempt to design a probe that could reach nearby stars and return data with transit times of decades rather than centuries. His news was surprising. The Parkes radio dish in Australia, then being used by the Breakthrough Listen SETI project, had detected a signal that seemed to come from Proxima Centauri. “What’s interesting,” said he, “is that when you move the dish off Proxima, the signal disappears.” You probably remember this episode, which had a brief moment in the news and may well live on among the conspiracy-minded in the wackier regions of cyberspace.

We know now that the signal was some form of radio frequency interference, commonly abbreviated RFI. In any case, our conversation was relatively tame because the idea of a terrestrial explanation seemed inevitable, no matter how tantalizing the first look at this signal. After all, with all the years of SETI effort since the original Project Ozma, was it likely that we would pick up a signal from the nearest of all stars? What were the odds that there would be a radio-using civilization so close to home?

Here I’m being deliberately provocative, because in fact we couldn’t know the odds. We know absolutely nothing about alien civilizations including whether or not they exist. To go science fictional, suppose Earth had triggered a nearby ‘lurker’ probe that had been in our Solar System monitoring our activities and had learned about our interest in the Alpha Centauri system. Would they possibly use a signal from Proxima as an introduction to first contact? Maybe from a lurker probe in that system? The scenarios can get as wild as anyone might wish. Best, then, to keep an eye on that signal.

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