While direct evidence of extraterrestrial life remains elusive unless aliens reside close to our solar system, the search for signs of life beyond Earth continues. Astrobiologists typically seek biological markers such as oxygen molecules and ozone in the atmospheres of exoplanets as indicators of potential life.

However, the presence of these chemicals doesn’t guarantee life; they could arise from unknown non-biological processes. More definitive proof of intelligent extraterrestrial beings might come from identifying signs of technological activities in space, known as technosignatures. Established in 1984, the Search for Extraterrestrial Intelligence (SETI) focuses specifically on detecting these technosignatures, particularly through radio signals.

From 2006 to 2020, the SETI@home project collaborated with researchers exploring excessive radio emissions from space via the Arecibo Telescope. Over 14 years, SETI@home collected approximately 400 days of observation time, resulting in billions of detected radio emissions. Unfortunately, most of these signals are likely due to radio frequency interference, benign celestial objects like pulsars or gas clouds, rather than a single extraterrestrial source.

To refine their data analysis, the team recently developed an algorithm designed to filter out interference and pinpoint signals from fixed sources. This advancement positions researchers to re-observe these locations using the 500-meter Fast Radio Telescope.

The algorithm’s goal is to differentiate between natural cosmic signals and potential technosignatures. The team established three criteria for detecting such signals: they must remain stable within a narrow frequency range, exhibit a consistent pulsation, and contain a periodic structure spanning several seconds.

A key consideration is that signals sent intentionally for detection may differ significantly from random radio waves emitted from an alien atmosphere. The principles governing these interactions, such as the Doppler shift, complicate the analysis. Researchers theorize that intelligent civilizations would generate radio signals at a near-constant frequency, easily distinguishable from natural noise.

In their algorithm development, researchers integrated artificial data points that simulate the potential detection of distinct technosignatures, referred to as birdie candidates. If a birdie is flagged for further analysis, it validates the algorithm’s effectiveness. Adjustments to the algorithm’s sensitivity were made based on whether birdies were included or excluded from deeper scrutiny.

To tackle the complexities of data filtering and scoring, the team divided tasks into manageable segments, allowing simultaneous processing on multiple machines. Running the algorithm on 2,000 connected processors, filtering took about 15 hours, while scoring required 1.6 days. Two iterations of the algorithm on SETI@home data were completed, including one with 3,000 birdies for comparative analysis. The Birdie system helped determine which algorithm settings surpassed specified energy thresholds, leading to the identification of 92 targeted signal candidates for re-observation using 23 hours of observation time gained through FAST.

Currently, work is ongoing to analyze these signals, and as of July 2025, researchers have re-observed 80 out of the 92 candidates. Although no direct evidence of extraterrestrial intelligence has been discovered yet, the team remains optimistic that future inquiries utilizing specialized radio telescopes will yield promising results. However, the high costs and demands associated with radio telescope usage mean that SETI will likely continue to collaborate with other astronomers to maximize data collection from available observations.

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