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A Signal from Proxima Centauri?

A Signal from Proxima Centauri?

Dec 19, 2020
Tags: SETI , Astrobiology , Español
Parkes Telescope
Parkes Telescope
By Seth Shostak, Senior Astronomer

Well, it might be aliens. Then again, in the tradition of Pogo it might just be us, led astray by our own technology.

A story in Britain’s Guardian newspaper today (December 18) reports that astronomers with the Breakthrough Listen Project – the comprehensive radio SETI search being run out of the University of California at Berkeley – has detected radio emissions from the direction of Proxima Centauri. That’s the closest star system to us, a mere 4.2 light-years away, and it’s known to be accompanied by at least two planets.

The signal was picked up by the Parkes 210-foot radio telescope in sheep country about 190 miles inland from Sydney, Australia. Because Proxima Centauri is only visible in the southern sky, you need a “down under” telescope to observe it.

But does this mean that SETI researchers have finally stumbled upon their holy grail, a radio emission that could only come from a deliberately constructed transmitter on another world? It’s possible, of course. But the Breakthrough Listen folk are careful not to indulge in any chest beating until the signal is subjected to additional observations.

So, what are the possible implications of this finding? Let us count the ways:

To begin, the signal apparently varies slightly in frequency, wobbling up and down the radio dial. So it’s not coming from an antenna bolted to the ground here on Earth. That immediately makes it non-terrestrial by definition, but still doesn’t certify it as alien.

Indeed, it just might be a telemetry signal from an orbiting satellite. The orbital motion of these satellites cause their transmissions to rise and fall in frequency, after all. And while you might think that the chances of accidentally tuning in a satellite are not great, you should think again. There are more than 2,700 functioning satellites buzzing our planet, providing information on the weather, imagery for Google Earth, GPS signals for navigation, and high-resolution photos for the military, just to name a few. This flood of information from hardware a few hundred miles above our heads is obviously important for a high-tech lifestyle, but it jams a lot of the radio spectrum. SETI scientists are trying to find a needle in a pile of pins.

But if it’s not a satellite signal, what else might it be? It’s possible that the signal is actually coming from something behind Proxima Centauri that just happens to line up with it. There’s an example of this coming your way next week, when Jupiter will seem to be intruding upon Saturn’s personal space as the two planets get close in the evening sky. On December 21, their separation will be only 6 arcmin, or about the width of a dime held at 20 feet. But of course Jupiter and Saturn won’t actually be close. You’d find 500 million miles of uninteresting space behind Jupiter before you encountered the ring thing. They just appear to line up.

So maybe that’s what’s going on: the signal’s not coming from Proxima Centauri, but from something else far beyond it. Maybe, but that would still be extremely interesting, as natural radio signals – the type produced by quasars, pulsars, and many other members of the cosmic bestiary – are not narrow-band. They’re not confined to a small range of frequencies, and this signal might be.

Yet another participant in this lineup is the possibility that what’s been found are merely natural radio emissions from a world having a strong magnetic field. In our own solar system, Jupiter’s noisy radio bursts have been studied for many decades. Maybe there’s such a beefy, magnetically laced planet orbiting Proxima Centauri?

That may seem plausible, but if you were to transport Jupiter to the distance of Proxima, its cacophonous outbursts would be roughly a thousand times weaker than the faintest signal our radio telescopes can detect. In other words, this explanation for the detection depends on there being an extraordinarily noisy world orbiting Proxima Centauri. Not impossible, but a bit unlikely.

Of course, there’s always the possibility that the signal is really, really local. A microwave oven in the break room of the Parkes radio telescope caused considerable consternation five years ago when it produced signals that, at first, suggested that something remarkable was happening in the distant cosmos. In fact, it was just someone heating up lunch.

So, given even this short laundry list, we see that there are several possible explanations for the signal that are, regrettably, rather prosaic. Yes, as long as we still don’t know, we should continue to consider the alien hypothesis viable. After all, any SETI detection is going to be dicey when we first make it … there will be plenty of calls for restraint intended to pacify the all-too-eager. But it’s reasonable to expect that someday one of these suspicious signals will, indeed, be the sought-after proof of intelligence on another world.

Caution is often a good idea, but one must be careful not to toss the baby with the bathwater. After all, this baby could change our concept of the cosmos.

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