Nobody believes it was ET telephoning, but radio astronomers admit they still have no explanation for a beam of radio waves that apparently came from the direction of the star Proxima Centauri.
“It’s kind of a technological signal. The question is, is it earth technology or technology from somewhere out there, ”said Sofia Sheikh, a graduate student at Pennsylvania State University who led a team that studied the signal and tried to decipher its origin. She is part of Breakthrough Lists, a $ 100 million effort funded by Yuri Milner, a Russian billionaire, to find extraterrestrial radio waves. The project has now encountered its most fascinating wage mess to date.
Proxima Centauri is an inviting prospect for “outside”.
It is the closest known star to the Sun, just 4.24 light years from Earth, and part of a triple star system called Alpha Centauri. Proxima has at least two planets, one of which is a rocky world that is only slightly more massive than Earth. It is located in the so-called habitable zone of the star, in which the temperatures should be conducive to the water, the substance of life, on its surface.
The radio signal itself, detected in Spring 2019 and previously reported in The Guardian, is in many ways an alien hunter’s dream. It was a narrow band signal with a frequency of 982.02 MHz as recorded at the Parkes Observatory in Australia. Nature, be it an exploding star or a geomagnetic storm, usually transmits over a wide frequency range.
“The signal only seems to appear in our data when we look towards Proxima Centauri, which is exciting,” said Ms. Sheikh. “That’s a threshold that has never been crossed by any signal we’ve seen before, but there are many limitations.”
Practitioners in the hopeful field of finding extraterrestrial intelligence, also known as SETI, say they have seen it all before.
“We have seen this type of signal before, and it always turns out to be RFI and radio frequency interference,” wrote Dan Werthimer, chief technologist at Berkeley SETI Research Center, which is not part of the Proxima Centauri study an email.
That thought was corroborated by his Berkeley colleague Andrew Siemion, who is the lead investigator for breakthrough lists. “Our experiment exists in a sea of clutter,” he said.
“My instinct in the end is that it will be of anthropogenic origin,” he added. “But so far we can’t fully explain it.”
So there’s nothing to see here, folks. Until there is. Notwithstanding the claims of biosignature gases on Venus and the stories of UFO sightings collected by the Pentagon, the discovery of life, let alone intelligence, would give a psychological thunderclap of cosmic and historical proportions.
False positives were part of SETI from the start when Frank Drake, then retired at Cornell and now at the University of California at Santa Cruz, pointed a radio telescope in Green Bank, W.Va. at a pair of stars in 1960 in hope to hear the radio waves from aliens. He saw a signal. Could it be so easy to discover that we are not alone?
It turned out to be a secret military experiment.
Sixty years later we are still officially alone and SETI as a company has gone through the wars economically and politically, even though technology has improved mankind’s ability to comb the near-infinite haystack of planets, stars and “magical frequencies” on which they are possibly send.
Announced with much fanfare by Mr. Milner and Stephen Hawking in 2015, Breakthrough Listen sparked what Dr. Siemion called a renaissance.
“This is the best time to do SETI,” he said.
The latest excitement started on April 29, 2019 when scientists from Breakthrough Listen turned the Parkes radio telescope on Proxima Centauri to monitor the star for violent flares. It is a small star known as a red dwarf. These stars are prone to such eruptions that could remove the atmosphere from a planet and make it uninhabitable.
In total, they recorded 26 hours of data. However, the Parkes radio telescope was equipped with a new receiver that can resolve narrowband signals of the type that SETI researchers are looking for. In the fall of 2020, the team decided to search the data for such signals. That role fell to Shane Smith, a student at Hillsdale College, Michigan and an intern at Breakthrough.
The signal that surprised the team appeared five times on April 29 in a series of 30-minute windows with the telescope pointed towards the Proxima Centauri. It has not appeared since. It was a pure unmodulated tone, which meant that it did not seem to carry any message other than the fact of its own existence.
The signal also showed a tendency to drift slightly in frequency during the 30-minute intervals, an indication that the signal is not on the surface of the earth but is often correlated with a rotating or orbiting object.
However, the drift does not correspond to the movements of known planets in Proxima Centauri. Indeed, if the signal is real, it could come from somewhere beyond the Alpha Centauri system. Who knows?
The subsequent non-appearance of the signal has led to comparisons with a famous detection known as “Wow! Signal, ”which appeared on a printout from the Big Ear radio telescope operated by Ohio State University in 1977. Jerry Ehman, a now retired astronomer, wrote, “Wow! “On the side of the printout when he saw it afterwards. The signal never reappeared or explained satisfactorily, and some people still wonder if it was a missed call from Out There.
About the Proxima signal, Dr. Siemion: “There were a few exclamations, but ‘wow’ wasn’t one of them.”
When asked what they were, he laughed.
“At first there were puzzled reactions from people, but it quickly calmed down,” he said.
Over a period of 24 to 48 hours at the end of October, the mood changed from curious and curious to “very serious scientific detective work”.
Ms. Sheikh, who expects to do her PhD next summer, is in charge of the detective work. She did her bachelor’s degree at the University of California at Berkeley to get into particle physics, but instead found herself in astronomy. She first heard about the Breakthrough Listen Project and SETI on Reddit when she was looking for a new student research project.
“I would say we were extremely skeptical at first and I remain skeptical,” she said of the alleged signal. But she added that it was “the most interesting signal to get through the Breakthrough List program.”
The team hopes to publish its results in early 2021.
The Parkes Telescope, which once relayed messages to the Apollo astronauts, is known for causing false alarms, says Dr. Werthimer. In a recent example, astronomers believed they had discovered a new astrophysical phenomenon.
“It was very exciting until someone noticed that the signals didn’t appear until noon,” he said. They came from a microwave.
Over the years, SETI astronomers have prided themselves on their ability to track down and eliminate the source of suspicious signals before the public knew about them.
This time her work was reported by The Guardian. “The public wants to know we understand,” said Dr. Siemion. But as he and Mrs. Sheikh point out, they are far from finished.
“In all honesty, there is still a lot of analysis that we need to do to make sure this thing is not a malfunction,” said Ms. Sheikh.
Part of the problem, she explained, is that the original observations were not made according to the standard SETI protocol. Typically, a radio telescope points at a star or other target for five minutes and then gently “nods” away from it for five minutes to see if the signal continues.
However, during the Proxima observations, the telescope pointed for 30 minutes and then moved far across the sky (about 30 degrees) for five minutes to a quasar, which the astronomers used to calibrate the brightness of the star’s flares. Such a large swing could have taken the telescope away from the source of the radio interference.
If all else fails, Ms. Sheikh said, they will try to reproduce the results by repeating the exact movements of the Parkes Telescope again on April 29, 2021.
“Because,” she said, “if it really comes from Proxima, then maybe once a year they want to say hello or something.” She continued, “But it’s more likely that there’s some sort of annual event at the visitor center or something that creates an environmental effect that doesn’t happen the rest of the year.”
The Proxima signal could turn into a legend like the Ohio State Wow! Signal, but in SETI there is always another day, another star.
It was fun, said Ms. Sheikh, even if the Proxima signal is interference.
“It’s extremely exciting, no matter what the outcome.”