SETI Advances: New Technique Filters Genuine Alien Signals from Terrestrial Interference

In a groundbreaking development for the Search for Extraterrestrial Intelligence (SETI), a team of researchers from the University of California, Berkeley, has introduced an innovative technique to identify potential radio signals of extraterrestrial origin. This cutting-edge method involves analyzing signals for indications that they have traveled through interstellar space, effectively eliminating the possibility of Earth-based radio interference.

The scientists at the University of California, Berkeley, have made significant strides in enhancing the search for extraterrestrial life. Their novel approach enables the distinction between potential alien signals and terrestrial interference by examining the signals’ journey through interstellar space.

Improved Method for Detecting Extraterrestrial Life

Researchers have introduced a new methodology that detects and verifies potential radio signals originating from extraterrestrial civilizations within our galaxy. This advancement in the field of Search for Extraterrestrial Intelligence (SETI) represents a significant leap forward and instills greater confidence in the future detection of alien life.

Current SETI initiatives primarily rely on Earth-based radio telescopes, which are susceptible to interference from terrestrial and satellite radio sources. False signals, resembling technosignatures from extraterrestrial civilizations, can emerge from various origins, including Starlink satellites, cellphones, microwaves, and even vehicle engines. Such interference has led to false expectations ever since the inception of the first dedicated SETI program in 1960.

Addressing Interference in the Quest for Alien Life

To differentiate authentic signals from false positives, researchers typically redirect the telescope’s focus to a different area of the sky and revisit the initial position multiple times to determine if the signal is recurring. However, there remains a possibility that the signal originates from an unusual terrestrial emission.

Researchers at the Breakthrough Listen project at the University of California, Berkeley, have devised an innovative technique to tackle this challenge. Their method carefully examines signals for indicators that they have traversed interstellar space, effectively eliminating the likelihood of Earth-based radio interference.

Breakthrough Listen, the most comprehensive SETI search endeavor, utilizes radio telescopes to monitor the skies of both the northern and southern hemispheres for technosignatures. The project focuses on thousands of individual stars in the Milky Way galaxy’s plane, which is deemed the most probable direction for a civilization to transmit a signal.

Andrew Siemion, the principal investigator for Breakthrough Listen and director of the Berkeley SETI Research Center (BSRC), which oversees the world’s longest-running SETI program, describes the technique as “one of the biggest advances in radio SETI in a long time.” He emphasizes its potential to differentiate a single signal from radio frequency interference, highlighting the significance of this capability when considering enigmatic signals like the famous “Wow!” signal, which often appear as isolated occurrences.

The renowned “Wow!” signal refers to a 72-second narrowband signal detected in 1977 by an Ohio-based radio telescope. The astronomer who discovered the signal, astounded by its unique characteristics, marked the data printout with a red ink “Wow!” The signal has not been observed since.

Siemion explains, “The first ET detection may very well be a one-off, where we only see one signal. 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.”

The research behind the new technique is detailed in a paper published on July 17 in The Astrophysical Journal. The paper’s authors include Bryan Brzycki, a UC Berkeley graduate student; Andrew Siemion; Imke de Pater, UC Berkeley professor emeritus of astronomy; and collaborators from Cornell University and the SETI Institute.

The new technique takes advantage of previous research on the interstellar medium (ISM), specifically how the cold plasma within it, primarily composed of free electrons, affects narrowband radio signals from sources like pulsars. Astronomers now possess a good understanding of how the ISM influences these signals, causing them to exhibit scintillation—fluctuations in amplitude over time—due to the slight refraction of radio waves by the intervening cold plasma. This interference occurs because the radio waves follow different paths, leading to positive and negative interference as they reach Earth.

Similar to the scintillation effect observed in the pinpricks of optical light from stars due to atmospheric interference, the ISM-induced scintillation affects narrowband radio signals. The Earth’s atmosphere does not cause such interference with planets, which are not point sources of light and, therefore, do not exhibit a twinkle.

Bryan Brzycki, the UC Berkeley graduate student involved in the research, has developed a computer algorithm capable of analyzing the scintillation patterns of narrowband signals. This algorithm identifies signals that undergo fluctuations in amplitude lasting less than a minute, indicating their passage through the ISM.

Imke de Pater explains the significance of this technique, stating, “This implies that we could use a suitably tuned pipeline to unambiguously identify artificial emission from distant sources vis-a-vis terrestrial interference. 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.”

Bryan Brzycki is currently conducting radio observations at the Green Bank Telescope in West Virginia to demonstrate the efficacy of the technique in swiftly distinguishing Earth-based radio signals and potentially detecting scintillation in narrowband signals—potential technosignatures.

The technique’s utility is limited to signals originating from over 10,000 light-years away from Earth, as these signals must pass through sufficient portions of the ISM to exhibit detectable scintillation. Signals originating from closer sources, like the BLC1 signal discovered by Breakthrough Listen in 2020, which seemed to originate from Proxima Centauri, our nearest star, would not display this effect.

The new technique, along with the scintillation technique, will be employed by Breakthrough Listen during SETI observations at the Green Bank Telescope and the MeerKAT array in South Africa.

The paper’s co-authors include James Cordes from Cornell University, Brian Lacki from BSRC, and Vishal Gajjar and Sofia Sheikh from both BSRC and the SETI Institute. Breakthrough Listen is managed by the Breakthrough Initiatives, a program sponsored by the Breakthrough Prize Foundation.

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More about SETI, extraterrestrial intelligence

• University of California, Berkeley
• The Astrophysical Journal
• Breakthrough Listen
• SETI Institute
• Green Bank Telescope
• MeerKAT Array
• Breakthrough Initiatives