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A mysterious signal that appeared to come from the nearest star to our own sun set scientists on a nearly year-long hunt to trace its origins.
The result? The signal was not from an alien world orbiting Proxima Centauri, but instead something much more mundane – possibly a radio, a telephone or even a computer located somewhere in Australia, according to two studies published this week in the journal Nature astronomy.
“It’s man-made radio interference from some technology, probably on Earth’s surface,” Sofia Sheikh, an astronomer at the University of California, Berkeley and co-author of both papers, told Nature.com. NPR tried to reach Sheikh, but failed.
The signal was first detected by a 210-foot (64-meter) radio telescope at the Parkes Observatory in New South Wales, Australia. “The Dish”, as the Australians call it, was the subject of a 2000 film of the same name starring Sam Neill.
The radio telescope is part of the Breakthrough List, the largest scientific research program to date to listen for extraterrestrial “techno signatures”. The program, launched in 2016, is based at the Berkeley SETI Research Center, located at the University of California, Berkeley, but involves radio telescopes worldwide.
How the search shifted from the stars back to Earth
“This was a really devastating signal,” Jason Wright, a professor of astronomy and astrophysics who is the 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 communication. But researchers eliminated that possibility – there were no planes in the area.
“This signal mimicked exactly what it was 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 says. It was on one particular frequency, whereas natural signals always appear over a range of frequencies. That alone is not surprising, he says, for there are plenty of easily identifiable man-made signals that must be constantly aimed at.
However, the signal did not remain at the same frequency – it drives, Wright says. “It’s something you expect from things that are actually in space,” he says, because the Earth’s spin causes a Doppler shift in frequency.
Making it even more exciting was 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 Earth and orbits the star in its “habitable zone”, where liquid water could exist on the surface.
But when researchers looked for the signal again, it was not there.
If it was not aliens, what was it then? “You can make some guesses based on how the frequency operates. That suggests it’s probably a cheap piece of electronics using a quartz oscillator,” Wright says.
Astronomers are used to being disappointed with false alarms
Seth Shostak, a senior astronomer at the SETI Institute, tells NPR that he ever hopes to one day discover an alien civilization, but his enthusiasm has been “dampened over time by realism.”
“We have had false alarms in the past, and you get really excited to only be disappointed a few days later when you finally find out that the signal was due. 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 region. But it went unnoticed until the following year. That was when Shane Smith, a bachelor at Hillsdale College in Michigan, discovered the signal while reviewing data collected from Parkes.
Smith, who worked as a research intern at 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 had to be interference,” he said Nature. “But after a while, I started thinking, these are exactly the kind of signals we’re looking for.”
Smith said he was excited but also skeptical, believing there was a simple explanation. “I never thought the signal would cause such a voltage,” he said.
Sometimes rummy mysteries are explained; sometimes they continue
It is not the first false alarm for scientists searching for extraterrestrial intelligence.
In 2015, for example, Russian astronomers using a radio telescope in Zelenchukskaya, at the foot of the Caucasus Mountains north of Georgia, discovered an interesting ray-shaped signal. It turned out to be from a Russian military satellite.
Most famously, in 1977, astronomers looking at transcripts from an observatory at Ohio State University, known as the Big Ear, discovered a 72-second eruption so unusual that a team member, Jerry Ehman, wrote “Wow!” on the data sheet.
The “wow! Signal” has never been explained satisfactorily, Wright says. “People have stumbled over it,” he says. “We are not going to suddenly have an aha moment where we find out what it was. I suppose it’s just going to be a mystery unless it repeats itself.”