SETI advance hopes to parse alien radio from Earthly static

Now, researchers at the University of California, Berkeley’s Breakthrough Listen project say they’ve found a way to pull these cosmos signals out of the noise of terrestrial interference, and it could revolutionize the search for alien life.

“I think it’s one of the biggest advances in radio SETI in a long time,” Andrew Siemion, principal investigator for Breakthrough Listen and director of the Berkeley SETI Research Center (BSRC), which operates the world’s longest running SETI program, said in a UC-Berkeley statement. “It’s the first time where we have a technique that, if we just have one signal, potentially could allow us to intrinsically differentiate it from radio frequency interference. That’s pretty amazing, because if you consider something like the Wow! signal, these are often a one-off.”

The Wow! signal, an especially powerful radio signal spotted by an astronomer in 1977 that many hoped would be the beginning of human-alien communication, has never been repeated, and its source is still a subject of intense debate.

The search for repeating signals from an identifiable source, meanwhile, is currently the only way we have to potentially spot alien signals amid the cacophony of Earth. It’s a time-consuming process, and even if follow-up signals are detected, the signal doesn't necessarily mean aliens; it could be the result of some unknown phenomena. 

That’s what makes the new technique, described this month in The Astrophysical Journal, so thrilling. 

The way the new technique works is by looking for scintillation — a repeated brightening and dimming of the signal's amplitude — in the radio signals hitting our radio telescopes.

Previous research found that radio signals from objects like pulsars would be affected by the cold plasma of the interstellar medium, warping and bending the radio signal so that when the radio waves eventually reach Earth, the distortion along the way produces positive and negative interference patterns in the signals or scintillations.

The important leap that Siemion and his colleagues made however is that these scintillations would also affect the very narrow-band radio signals that SETI has been looking for since the 1960s. Since these scintillating signals are definitionally coming from interstellar space and beyond, these scintillations could be the key to algorithmically filtering out human-produced radio interference on Earth (whose signals do not scintillate), revealing only those signals that don't originate on Earth.

“The first ET detection may very well be a one-off, where we only see one signal,” Siemion said. “And if a signal doesn’t repeat, there’s not a lot that we can say about that. And obviously, the most likely explanation for it is radio frequency interference, as is the most likely explanation for the Wow! signal. Having this new technique and the instrumentation capable of recording data at sufficient fidelity such that you could see the effect of the interstellar medium, or ISM, is incredibly powerful.”

UC Berkeley graduate student Bryan Brzycki helped the project by developing a Python script that implements this algorithm by analyzing the scintillations of narrowband radio signals and isolating those that cycle through dimming and brightening in less than a minute, which indicates that these signals passed through the interstellar medium.

“This implies that we could use a suitably tuned pipeline to unambiguously identify artificial emission from distant sources vis-a-vis terrestrial interference,” said Imke de Pater, UC Berkeley professor emeritus of astronomy, who serves as Brzycki's graduate advisor. “Further, even if we didn’t use this technique to find a signal, this technique could, in certain cases, confirm a signal originating from a distant source, rather than locally. This work represents the first new method of signal confirmation beyond the spatial reobservation filter in the history of radio SETI.”