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A mysterious signal that seemed to emanate from the star closest to our own sun put scientists on a nearly year-long hunt to find its origin.
The result? The signal was not coming from an alien world surrounding Proxima Centauri, but rather from something much more mundane – perhaps a radio, phone or even a computer located somewhere in Australia, according to two studies published this week in the newspaper. Nature astronomy.
“This is man-made radio interference from technology, probably on the surface of the Earth,” Sofia Sheikh, University of California, Berkeley astronomer and co-author, told Nature.com of the two articles. NPR tried to reach Cheikh but was unsuccessful.
The signal was first detected by a 210-foot (64-meter) radio telescope at Parkes Observatory in New South Wales, Australia. “The Dish”, as Australians call it, was the subject of a film of the same name in 2000 starring Sam Neill.
The radio telescope is part of Breakthrough Listen, the largest scientific research program ever to listen to alien “technosignatures”. The program, launched in 2016, is based at the Berkeley SETI Research Center, located at the University of California at Berkeley, but involves radio telescopes from around the world.
How research went from the stars to the Earth
“It was a really pernicious signal,” Jason Wright, professor of astronomy and astrophysics and director of the Penn State Extraterrestrial Intelligence Center, told NPR.
The signal, which lasted about five hours at 982 megahertz, was at a frequency normally reserved for air communications. But the researchers ruled out that possibility – there were no planes in the area.
“That signal mimicked exactly what they were trying to find. And it’s really rare. I mean, it’s the first time in years that they’ve seen something like this,” Wright said.
It had clear signs of being produced by technology, he said. It was at a specific frequency, whereas natural signals always appear over a range of frequencies. That alone is not surprising, he says, as there are a lot of easily identifiable human-made signals that need to be filtered out all the time.
However, the signal didn’t stay at the same frequency – it drifted, Wright says. “This is something you would expect from things that are actually in space,” he says, as the Earth’s rotation causes a Doppler shift in frequency.
What’s even more intriguing is that Proxima Centauri, a red dwarf star just 4.2 light years from Earth, has two known planets. One of these planets has a minimum mass very close to that of the Earth and orbits the star in its “habitable zone”, where liquid water could exist on the surface.
But when the researchers looked for the signal again, it wasn’t there.
If they weren’t aliens, then what were they? “You can make guesses based on the frequency drift. This suggests that this is probably a cheap electronic device using a crystal oscillator,” says Wright.
Astronomers are used to being disappointed with false alarms
Seth Shostak, senior astronomer at the SETI Institute, told NPR that he still hopes to someday detect an alien civilization, but his enthusiasm has been “tempered over time by realism.”
“We have had false alarms in the past, and you are all excited to be disappointed a few days later when you finally understand that the signal was due to Homo sapiens, not the Klingons, ”says Shostak.
The 2019 signal was detected by the radio telescope as it spent 26 hours listening in the Proxima Centauri area. But it went unnoticed until the following year. It was then that Shane Smith, an undergraduate student at Hillsdale College in Michigan, discovered the signal while sifting through data collected from Parkes.
Smith, who worked as a research intern with Breakthrough Listen, told his supervisor, University of California, Berkeley, astronomer Danny Price, who posted it on the Breakthrough Listen Slack channel. The price was initially skeptical.
“My first thought was that it must be interference,” he said. Nature. “But after a while I started to think, this is exactly the kind of signal we’re looking for.”
Smith said he was excited but also skeptical, thinking there was a simple explanation. “I never thought the signal would cause such excitement,” he said.
Sometimes the mysteries of space are explained; sometimes they continue
This isn’t the first false alarm for scientists looking for alien intelligence.
In 2015, for example, Russian astronomers using a radio telescope in Zelenchukskaya, at the foot of the Caucasus Mountains in northern Georgia, discovered an interesting beam-shaped signal. It turned out to be from a Russian military satellite.
Most famous, in 1977, astronomers looking at impressions from an Ohio State University observatory known as the Big Ear detected a 72-second burst so unusual that a member of the team, Jerry Ehman, scrawled “Wow!” on the technical sheet.
The signal “Wow! Has never been explained satisfactorily, says Wright. “People looked at it,” he says. “We’re not suddenly going to have an aha moment where we find out what it was. I suspect it will just have to be a mystery unless it happens again.”