Wednesday, December 1

Why are astronomers interested in this mysterious signal

In the 1997 movie Contact A scientist, played by actress Jodie Foster, detects a radio signal, the first communication of a alien civilization.

That story, written by Carl Sagan and his wife Ann Druyan, is fiction, of course. But the search for such a sign is not such a crazy story.

Real scientists look up to the sky, using powerful radio telescopes, expecting to hear even a faint whisper of a radio signal from one of our heavenly neighbors.
Hubble's new shot of Proxima Centauri, our closest neighbor.
Hubble’s 2013 take of Proxima Centauri, our closest neighbor. (ESA / Hubble and NASA)

And indeed, the British newspaper The Guardian published in December a recent report of a broadcast coming from Proxima Centauri, the star closest to our own.

The source of the story is not a scientific article, but appears to have been leaked by an anonymous source. The claim of an intercepted signal, if it turns out to be truly a sign of extraterrestrial intelligence, would be one of the most momentous discoveries of all time.

But this reported signal is almost certainly not that.

In April and May 2019, the 64 meters wide Parkes Radio Telescope, located in Australia, was recording radio transmissions from the direction of the nearby star Proxima Centauri. Over the course of hours, the telescope recorded data from the star for 30-minute intervals, before moving away to look in a different direction.
extraterrestrial signal detected in the parkes telescope
The Parkes radio telescope, located in Parkes, New South Wales, detected the signal in 2019 from the nearby star Proxima Centauri. (extraterrestrial signal detected in the parkes telescope)

This procedure, called “nodding,” is used to establish that any observed signal is coming from a particular direction, rather than just random radio noise.

During five of these half-hour intervals, the signal was observed while the antenna was pointed at Proxima Centauri, and was not detected at all when it was pointed in another direction.

This signal was not immediately noticed; More than a year passed after the data was recorded that Shane Smith, an intern for Breakthrough Listen, a project funded by billionaire Yuri Milner that seeks to find signs of alien life, found it buried in the telescope recordings. This was in late October 2020.

So what, exactly did you see?

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It was a radio signal at a single frequency, specifically 980.002 MHz. The signal deviated slightly over time, which is what you would expect if it were emitted by a planet or moon orbiting a star. It was observed to have originated in a small portion of the sky, about half the diameter of the full moon, centered on Proxima Centauri.

First of all, it is important to note that astronomers think that the signal is highly unlikely to be caused by aliens trying to communicate with us. Even the researchers involved in Breakthrough Listen don’t make that claim.

It is also important to remember that this observation has not yet been published in a peer-reviewed journal, so it has not been subjected to a rigorous scientific review. Instead, the online rumor stemmed from a rumor about the signal that was leaked to The Guardian, which published it on December 18.

Still, it’s interesting to do the thought experiment on whether the signal was really a communication from a civilization orbiting a distant star.

Proxima Centauri is our astronomical neighbor, just 4.2 light years away. It is a red dwarf star, so faint that it is not visible to the human eye.

Proxima Centauri is known to have at least two planets. One is roughly seven times the mass of Earth, while the other is only 20% more massive than Earth. The smallest planet orbits very close to the star, circling it in just 11 days.

An artist’s impression of a flare from our neighboring star Proxima Centauri is seen expelling material to a nearby planet. (CNN)

Proxima Centauri is dim compared to the Sun, and this smaller planet is located at the correct distance from its star to possibly have liquid water. It’s in what’s called the Goldilocks area, not too hot, not too cold, but it’s okay.

This makes the planet exciting for astronomers to study. A radio signal from a possibly habitable world could be the first proof that we are not alone in the universe. But we must not rush.

For one thing, the smaller planet orbiting Proxima Centauri is close enough to be affected by sudden bursts of energy called parent star flares. These flares are likely to bathe the planet in enough radiation to kill any familiar life forms and would also strip away any possible atmosphere.

The planet would also be “blocked by the tides”, with one face always facing the star, just as we see only one face of the Moon. It turns out that this planet is highly unlikely to be a pleasant place.

Also, the radio signal is simply much more likely to be of terrestrial origin. We live in a world of radio signals, from AM and FM broadcasts of current hits to cell phones and errant broadcasts from microwave ovens. And, with its frequency of 980.002 MHz, it is very curious that the frequency of the signal is so close to a whole number. If this is a sign of extraterrestrial life, this would suggest that it counts time in seconds like we do.

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Also, the signal is single frequency. Radio transmissions must vary in intensity or frequency to transmit information, and it doesn’t, so if it’s an alien trying to communicate, it’s clearly not trying to tell us much.

So sadly, this potentially exciting sign likely has a common cause. But that’s beside the point. The important thing is that, generated by aliens or not, humanity detected the signal. We are looking out into the cosmos, actively searching to see if we have cosmic neighbors. And this is good. It’s something we should be doing.

One day, that scene acted in Contact will be real. Some investigator will be surprised by a weak, screeching signal from the sky, a signal that will change everything. But only if we are listening. When ET makes that call, someone should be answering the phones.

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