Researchers working on Breakthrough Listen, a project devoted to the search for alien civilizations, detected the signal in April or May this year using the Parkes radio telescope in Australia. They have since been hard at work deciphering its cause. Though it likely has a mundane explanation, the researchers are intrigued about the signal's very peculiar nature.
The beam, which has not been spotted again since its detection, appears to have come from Proxima Centauri. The red dwarf sits around 4.2 light-years from Earth and has two known planets orbiting it. Along with an apparent shift in the signal's frequency, its direction may indicate the presence of a third planet or even hint at the existence of an advanced alien civilization.
But other astronomers remain cautious about the finding, stating that the signal might have a terrestrial origin.
The researchers are currently preparing a research paper on the findings and are keeping details under wraps. But based on what they've revealed so far, the signal appears to be an exceptional find. "It is the first serious candidate since the ‘Wow! signal’," the researchers said.
The "Wow! signal" was a strong short-lived narrowband radio emission detected in 1977 during a SETI survey at the Big Ear Radio Observatory in Ohio. The enigmatic signal generated a flurry of excitement and earned the name "Wow!" after Jerry Ehman, the astronomer who discovered it, wrote the interjection next to the data. It was the most intriguing radio signal that SETI scientists discovered.
Now, Breakthrough Listen's finding may be rivaling that one. The signal has not been attributed to any man-made source, fueling speculation that it is a "technosignature" – an indicator of technologically advanced activity. Breakthrough Listen was launched in 2015 to look for technosignatures but they have remained elusive. (Related: Astronomers say “technosignatures” can be used to find advanced alien civilizations.)
However, many other scientists are skeptical that the mysterious signal is anything other than man-made. Astrobiologist Lewis Dartnell of the University of Westminster in the U.K. said that the signal is not likely to have originated from an alien civilization.
"We've been looking for alien life for so long now and the idea that it could turn out to be on our front doorstep, in the very next star system, is piling improbabilities upon improbabilities," said Dartnell.
If there were intelligent alien life as close as Proxima Centauri, then the galaxy is probably teeming with life, according to Dartnell. "The chances of the only two civilizations in the entire galaxy happening to be neighbors, among 400 (billion) stars, absolutely stretches the bounds of rationality," he added.
Moreover, there are only two known planets orbiting Proxima Centauri – one is an inhabitable gas giant while the other one is thought to be a rocky planet roughly 17 percent more massive than Earth. Known as Proxima b, the planet is located in its host star's habitable zone, the orbital region around a star where the conditions are just right to support liquid water – a prerequisite for life.
But Proxima b is believed to be inhospitable despite its seemingly cozy location. In 2017, scientists from the National Aeronautics and Space Administration (NASA) found that if Proxima b had an Earth-like atmosphere, it could easily have been stripped away by the intense solar flares generated by its host star. The planet, estimated to be four billion years old, could have lost its entire atmosphere in 100 million years.
"It is possible there are other planets, slightly further from the star, that have yet to be discovered by astronomers, but they are likely too far away for liquid water to form," Dartnell said. (Related: Nearby exoplanet could potentially support life.)
Pete Worden, former director of NASA's Ames Research Center in California and executive director of the Breakthrough Initiatives, also said that the researchers already detected several bizarre signals. All of these were likely caused by human-made interference that scientists cannot yet fully explain.
But Worden noted that further analysis is underway and that it is important to wait for the researchers to unveil the entirety of their findings before ruling out any possibilities. Dartnell also said that he would "love to be proved wrong."
Read more stories about mysterious discoveries in space at Unexplained.news.