On April 29, 2019, an Australian telescope detected a radio signal that appeared to be coming from the closest star to our Solar System, Proxima Centauri.
Sofia Sheikh, an astronomy postdoc at the University of California, Berkeley, recalls her excitement when she first saw the signal. “I looked at it and I was like, wow this is exactly what we told our algorithm to return to us,” Sheikh tells Inverse.
The signal’s features looked a lot like a signal coming from deep space, perhaps produced by an alien civilization. Following its discovery, a team at Breakthrough Listen, a private effort that is part of the search for extraterrestrial intelligence (SETI) research field, went on a yearlong journey to find out where the signal was coming from.
Although the signal turned out to be interference coming from Earth, the detective work involved led to the development of better techniques involved in the search for alien life.
The work is detailed in two studies published Monday in the journal Nature Astronomy.
WHAT’S NEW — Since it was established in 2016, Breakthrough Listen has tuned in to the cosmos to detect any type of technological signal that may be coming from an alien civilization.
But this signal, dubbed BLC1 for Breakthrough Listen candidate 1, was the first time a detection sparked a detailed search for its source because of its intriguing characteristics that match up with a possible alien technosignature.
The signal was detected by the 64-meter Parkes Observatory radio telescope in southeastern Australia. The telescope had been monitoring nearby star Proxima Centauri for 26 hours to observe the star’s flares when it detected BLC1.
Andrew Siemion, director of the Berkeley SETI Research Center, explains that the most likely source of narrowband radio signals is always terrestrial interference.
“We know that technology ubiquitously produces this kind of emission because our own technology does so,” Siemion tells Inverse. “Usually we are able to confirm that they are interference in minutes or hours, but BLC1 was much more confounding.”
Out of a total of more than 4 million signals, BLC1 seemed to come from the star itself as it seemed to only appear when the telescope was pointed towards Proxima Centauri. It was near 982 megahertz and lasted about 5 hours. Usually signals from airplanes or satellites last for about half an hour as they move from that region of the sky.
The signal also had a drifting motion, whereby it drifts in frequency over the course of the observation. This indicates that something is moving relative to the telescope.
“We usually don't get to go through as many of those steps because so far we haven't found too many things that are interesting enough to do that,” Sheikh says.
Think of the needle in a haystack analogy. “Our algorithms will go through a part of that haystack and return kind of a suspiciously shaped piece of hay,” Sheikh says. “But just because the algorithm gave something to us, doesn't mean that it's immediately for sure from space.”
Thus began the investigation process:
- The team peformed follow up observations of Proxima Centauri to try and find the signal again
- They also looked to try and find a source to produce that drift in motion like a car on a nearby highway or planet
- Finally, they tried to characterize the signal and look for more reappearances
After looking through archival data, the team found that that signal had not appeared before in observations of Proxima Centauri. Its drift motion also did not match up with a signal coming from the star, nor an easily explained piece of human technology.
“And so we had to fall back on the explanation that sometimes drifts can come from malfunctioning electronics or electronics that are heating and cooling,” Sheikh says. “So it became likely that the signal was stationary relative to this telescope, so somewhere on the surface of the Earth, and was something that was malfunctioning.”
The malfunctioning equipment was likely within a few hundred kilometers of the telescope.
“You could keep going down the rabbit hole and keep analyzing to try and figure out exactly which piece of human technology, or whose Wi-Fi router caused the signal,” Sheikh says. “But from our perspective, now that we're able to pretty conclusively say this is coming from some human technology on the surface of the Earth, we'd prefer to spend our effort on finding the next signal.”
WHY IT MATTERS — While the team may not have found alien life yet, this recent venture led them to develop a series of new techniques that they can use in search of technosignatures in the future.
“It was a great test run of our capabilities,” Siemion says.
It is very rare that a signal passes the initial cutoff, and requires that the team delves deeper into its origin.
“I like the process of investigation,” Sheikh says. “I actually think that's a big part of the scientific rigor of the search for extraterrestrial intelligence.”
WHAT’S NEXT — The team at Breakthrough Listen expect to find more of these signals in the future, and will even keep their telescopes aimed at Proxima Centauri.
“Proxima Centauri remains a very compelling target for technosignature searches — it is the nearest star to the Earth and hosts at least one planet in its habitable zone,” Siemion says. “We have a number of new observations planned, including using the MeerKAT array in South Africa, which is significantly more sensitive than Parkes.”
Sheikh is ready to take on more investigative work. “We’ve come incredibly far,” Sheikh says.
Today’s SETI observatories can detect thousands of times more frequencies than they were able to process in previous decades and look for signals that are thousands of times narrower than before, according to Sheikh.
“So, any amount of the search space that we can cover, the amount of hay that we can go through in the haystack, it's thousands of times bigger than it was in the 60s and 70s,” Sheikh says. “Every year, we're searching so many more targets, so many more frequencies.”
Abstract: The aim of the search for extraterrestrial intelligence (SETI) is to find technologically capable life beyond Earth through their technosignatures. On 2019 April 29, the Breakthrough Listen SETI project observed Proxima Centauri with the Parkes ‘Murriyang’ radio telescope. These data contained a narrowband signal with characteristics broadly consistent with a technosignature near 982 MHz (‘blc1’). Here we present a procedure for the analysis of potential technosignatures, in the context of the ubiquity of human-generated radio interference, which we apply to blc1. Using this procedure, we find that blc1 is not an extraterrestrial technosignature, but rather an electronically drifting intermodulation product of local, time-varying interferers aligned with the observing cadence. We find dozens of instances of radio interference with similar morphologies to blc1 at frequencies harmonically related to common clock oscillators. These complex intermodulation products highlight the necessity for detailed follow-up of any signal of interest using a procedure such as the one outlined in this work