When astronomers search for life beyond Earth, they usually start with a familiar question: could a particular exoplanet support biology like ours? Liquid water, mild temperatures, and Earth-like conditions often dominate the conversation. However, a recent study argues that when it comes to finding intelligent life, habitability may be beside the point.
Instead of limiting themselves to potentially life-friendly worlds, researchers working with the Breakthrough Listen initiative examined radio observations of 27 exoplanets as they passed through secondary eclipses—moments when a planet slips behind its host star from Earth’s perspective.
The study was built on the idea that if a technologically capable civilization were transmitting radio signals from a planet or its immediate surroundings, those signals should briefly disappear during the eclipse, then reappear once the planet emerged again. That on-off signature would be difficult to mistake for natural astrophysical noise.
This approach allowed researchers to cast a much wider net by recognizing that, in principle, technology does not require Earth-like climates to exist.
“While this study does focus particularly on exoplanets (both candidate and confirmed), the physical characteristics of each target was not considered in the target selection process, and thus includes a range of non-terrestrial bodies,” researchers write. “The search for technosignatures as a sign of intelligent life is, in effect, a search for transmitter technology: technology that need not be located on or around traditionally habitable, nor necessarily inhabited, astronomical bodies.”
This perspective shaped one of the most unique SETI surveys to date. Rather than asking which exoplanets might resemble Earth, researchers asked where alien transmitters would be easiest to verify. The answer led them to eclipses.
In a paper published on arXiv, researchers analyzed radio observations of 27 exoplanets as they passed behind their host stars during secondary eclipses—brief moments when a planet disappears from view and provides a rare, powerful test for detecting artificial signals.
If a technologically capable civilization were transmitting radio signals from a planet, a moon, or even an artificial platform nearby, those signals should abruptly cut off as the planet slipped behind its star—then reappear when it emerged again.
Such a clean on-off pattern, synchronized with a precisely predicted celestial event, would be extremely difficult to explain as a natural astrophysical phenomenon or as human-made interference.
This approach marks a departure from most traditional SETI searches, which typically scan stars continuously for unusual radio emissions and then struggle to rule out terrestrial contamination. By tying the search to a known geometric event, the eclipse method offers a built-in verification mechanism.
To test the idea, researchers analyzed archival data collected by the Murriyang radio telescope—formerly known as Parkes—in Australia between 2018 and 2022. Using its ultra-wideband receiver, the team scanned a broad slice of the radio spectrum from 704 to 4,032 megahertz, covering frequencies commonly considered promising for interstellar communication.
The team cross-referenced these observations with data from NASA’s Transiting Exoplanet Survey Satellite, or TESS, identifying 27 confirmed or candidate exoplanets that underwent secondary eclipse during 30-minute observing windows.
Significantly, the targets were selected purely on geometric timing, not on whether the planets were Earth-like. The sample includes gas giants, ultra-hot worlds, compact systems, and planets orbiting a wide range of stellar types.
Each target was observed using a carefully structured cadence. The telescope alternated between pointing directly at the star system and at a nearby patch of sky offset by half a degree. This “on-source/off-source” pattern allows researchers to quickly identify radio frequency interference (RFI) from Earth-based sources, such as satellites, aircraft, and telecommunications systems.
Once collected, the data were processed using TURBOSETI, a specialized software pipeline developed to detect narrowband, drifting radio signals—exactly the kind expected from engineered transmitters rather than natural cosmic sources. The analysis searched for signals with specific Doppler drift rates indicative of relative motion between the transmitter and Earth.
The scale of the search was immense. The pipeline initially flagged nearly two million potential signals, which automated filters narrowed to 14,639 events requiring closer scrutiny.
Each of these was then examined visually, with researchers looking for narrowband drifting signals that appeared only during on-source observations and not in reference pointings—criteria designed to identify potential technosignatures, including those that might be interrupted during a predicted eclipse.
Unfortunately, none passed all three tests or confirmed any technosignatures from distant alien worlds.
Despite the lack of a detection, the researchers emphasize that the outcome is far from a failure. By not finding signals, the team was able to place quantitative limits on what kinds of alien transmitters current instruments could realistically detect.
Using standard metrics in the field, the study calculated the minimum Equivalent Isotropic Radiated Power, or EIRP, required for a transmitter at each exoplanet to be detectable from Earth. Across the sample, those thresholds ranged from about one trillion watts to more than a quadrillion watts, depending on distance and observing conditions.
For context, the now-collapsed Arecibo Observatory—the most powerful planetary radar ever built by humanity—had a transmission capability of roughly 20 trillion watts. According to the study, more than half of the surveyed exoplanets would have been detectable if they hosted transmitters comparable to Arecibo’s peak power.
The team also calculated a broader figure of merit used by Breakthrough Listen to compare different technosignature surveys. By that measure, the project meaningfully expanded the parameter space explored by SETI, even without a confirmed signal.
Beyond the numbers, the study’s most important contribution may be methodological. By demonstrating that eclipse-based technosignature searches are feasible using existing data, the research opens a new pathway for future surveys—one that does not depend on assumptions about alien biology or habitability.
This is especially important as astronomers increasingly recognize that advanced civilizations, if they exist, may not confine their technology to planetary surfaces. Transmitters could be located in orbit, on moons, or on artificial structures that have little to do with traditional concepts of life-friendly environments.
Looking ahead, the researchers suggest several ways to improve the approach. Future observations could cover broader frequency ranges, search for weaker signals by lowering detection thresholds, and stack data around eclipse times to amplify faint but consistent emissions. Improved algorithms for filtering radio interference, many of which are already under development, could further reduce false positives.
Ultimately, the silence detected in the study does not rule out intelligent life elsewhere in the universe. However, it does refine where—and how—scientists should listen next.
In reframing SETI as a search for technology rather than biology, the work underscores a subtle shift in perspective. If alien intelligence exists, it may not live where we expect—or look anything like us. However, its machines, if they transmit, may still leave fingerprints we can learn to recognize.
“Calculations suggest that if our targets had the 20TW transmission capabilities of the late Arecibo radio telescope, 59.3% would be capable of sending a signal powerful enough to be detectable from Earth,” researchers conclude. “These are the first statistical limits on hypothesized technosignatures during exoplanetary eclipses for TESS targets observable in the southern hemisphere.”
Tim McMillan is a retired law enforcement executive, investigative reporter and co-founder of The Debrief. His writing typically focuses on defense, national security, the Intelligence Community and topics related to psychology. You can follow Tim on Twitter: @LtTimMcMillan. Tim can be reached by email: tim@thedebrief.org or through encrypted email: LtTimMcMillan@protonmail.com