The assumption that drives SETI, the Search for Extraterrestrial Intelligence, is that the primary evidence for extraterrestrial civilization will be electromagnetic: a radio or optical signal transmitted across interstellar distances, detected by a sufficiently sensitive receiver pointed in the right direction at the right time.
This assumption has produced fifty years of systematic sky surveys, thousands of hours of telescope time, the Allen Telescope Array, the Breakthrough Listen program with its hundred-million-dollar budget, and a complete absence of confirmed detections.
Whether the absence of confirmed detections means no transmitting civilizations exist, or means that electromagnetic transmission is not how advanced civilizations communicate, or means that we have been listening at the wrong frequencies or looking at the wrong places, is a question that the fifty-year null result raises without answering. The Fermi Paradox, which notes the apparent contradiction between the high probability of extraterrestrial civilizations existing somewhere in the galaxy and the complete absence of detected evidence for any of them, remains unresolved despite decades of serious scientific engagement.
A different research tradition, smaller and less funded but documented in the same peer-reviewed literature, starts from a different assumption. The Search for Extraterrestrial Artifacts, SETA, proposes that the primary evidence for extraterrestrial civilization is more likely to be physical than electromagnetic, and that the specific physical objects most likely to represent extraterrestrial technology are not unambiguously alien in appearance but are instead objects that could be mistaken for natural phenomena by a civilization that does not know what to look for.
SETA’s specific logic deserves development before its specific candidate locations are examined, because the logic is what distinguishes it from both SETI and from the popular extraterrestrial spacecraft hypothesis.
Why Probes Rather Than Signals
The fundamental argument for SETA over SETI is energetic and temporal.
Electromagnetic signals travel at the speed of light. An interstellar civilization attempting to survey the galaxy for life-bearing planets by signal transmission must either transmit continuously in all directions at enormous power cost, or must transmit directionally toward specific targets that it has identified as promising. If it transmits continuously in all directions, the signal power required to be detectable at interstellar distances is extraordinary and the energy cost over millions of years of transmission is prohibitive for any known energy source. If it transmits directionally, it must already know which stars have life-bearing planets before it transmits, which requires a prior survey capability that electromagnetic transmission alone cannot provide.
Physical probes solve both problems simultaneously. A probe sent to a target star system requires energy expenditure only at launch and course correction. Once deployed, it operates at no additional energy cost to its originating civilization. It can remain operational for millions or billions of years if constructed from appropriate materials. It can collect and transmit data continuously at very low power, since it is transmitting from within the target system rather than across interstellar distances. And it can be launched toward any star system identified as potentially interesting from astronomical observation, without requiring prior knowledge of the system’s biological status.
The von Neumann probe concept, proposed by mathematician John von Neumann and subsequently developed by physicist Frank Tipler, extends this logic further: a self-replicating probe that uses materials from the target system to build copies of itself and send them to neighboring systems could survey the entire galaxy in a time period that is short relative to the galaxy’s age, using only the initial energy expenditure of launching the first probe. The absence of evidence for von Neumann probes is itself one of the proposed resolutions to the Fermi Paradox, but the absence of evidence for self-replicating probes does not imply the absence of non-replicating surveillance probes of the type Benford describes.
The specific argument Robert Freitas made in his 1983 paper in the Journal of the British Interplanetary Society, the foundational SETA paper, is that a civilization conducting a reconnaissance survey of the solar system would place a probe in a stable, long-duration orbit that required minimal maintenance, in a location where it had good observational coverage of the target planet, and where it would not obviously attract attention. Co-orbital positions, Trojan points, and Earth-Moon Lagrange points all meet these criteria.
James Benford and the Co-Orbital Hypothesis
James Benford is a plasma physicist whose career includes work at the Lawrence Livermore National Laboratory and whose published work on microwave energy transmission for spacecraft propulsion is documented in the peer-reviewed literature. His co-orbital surveillance paper, published in Acta Astronautica in 2021, represents the most recent and most formally developed statement of the SETA hypothesis applied to Earth’s specific orbital environment.
Benford’s specific argument is that Earth co-orbitals, objects that orbit the Sun at approximately the same distance as Earth and therefore maintain relatively stable positions near Earth over long time periods, are the most probable locations for a surveillance probe deployed by an extraterrestrial civilization conducting a long-duration reconnaissance of the solar system.
The specific co-orbital objects of interest are the Earth Trojans, objects that orbit at the L4 and L5 Lagrange points sixty degrees ahead of and behind Earth in its orbit, and the Earth co-orbital asteroids, objects whose orbital period is close enough to Earth’s that they spend extended periods in Earth’s vicinity before diverging.
The Earth Trojans are particularly significant for the SETA hypothesis because objects at the Lagrange points are gravitationally stable over very long periods, meaning a probe placed there does not require active propulsion to maintain its position. The L4 and L5 points are the most stable parking locations in Earth’s orbital environment for a long-duration object. A civilization placing a surveillance probe in Earth’s vicinity for a multi-million-year deployment would select exactly these locations.
The current catalog of Earth Trojans is small. Only one confirmed Earth Trojan asteroid, 2010 TK7, has been identified. The low number reflects observational limitations rather than the actual population: the Earth Trojan regions are difficult to survey because they are close to the Sun’s direction from Earth’s perspective, making ground-based observation challenging. The Large Synoptic Survey Telescope, now operational as the Vera Rubin Observatory in Chile, is expected to substantially increase the known Earth Trojan population through its systematic survey capability.
Benford’s specific proposal is straightforward: survey the known co-orbitals and Lagrange point objects with both optical and radar instruments, looking for objects whose spectral properties, radar cross-section, or orbital behavior is inconsistent with natural asteroid composition and dynamics. Anomalous objects deserve follow-up investigation rather than default classification as unusual natural asteroids.
The cost of this survey program is low relative to the significance of a positive result. The negative result, finding that no co-orbital objects show anomalous properties, is itself informative: it establishes that no extraterrestrial probe with detectable physical properties has been placed in Earth’s orbital neighborhood, which constrains the parameter space of extraterrestrial technological activity in the solar system.
Freitas and the Documented SETA Tradition
The SETA research tradition predates Benford’s paper by four decades and has produced a documented body of peer-reviewed literature whose public profile is inversely proportional to its scientific seriousness.
Robert Freitas and Francisco Valdes published the first systematic SETA survey in 1983, reporting on their optical search for probes at the Earth-Moon Lagrange points using the 0.8-meter telescope at Kitt Peak National Observatory. They found no anomalous objects in their survey area, which covered approximately 1.5 square degrees around the L4 and L5 points. Their survey’s sensitivity was limited by the technology available in 1983, and their null result established only that no probes brighter than approximately 17th magnitude were present in the surveyed area at the time of observation.
Freitas subsequently published a series of papers in the Journal of the British Interplanetary Society developing the theoretical framework for SETA and identifying the specific physical properties that would distinguish an artificial probe from a natural asteroid. His 1985 paper on the physical and chemical signatures of probes constructed from asteroid materials provides the specific analytical framework for evaluating candidate objects.
The specific challenge Freitas identified is that a long-duration probe constructed to survive millions of years in the solar system’s radiation and micrometeorite environment would likely be constructed from the same materials available in the solar system, meaning its bulk composition would not obviously distinguish it from a natural asteroid. The distinguishing features would be more subtle: specific geometric regularity, anomalous density for its size and composition, specific radar reflectivity patterns inconsistent with natural surface texture, or orbital behavior showing evidence of active station-keeping.
Paul Davies, the physicist and astrobiologist at Arizona State University cited in the source, published a more recent treatment of the SETA concept in his 2010 book The Eerie Silence, arguing that the search for extraterrestrial intelligence should expand beyond electromagnetic signals to include physical artifacts, biological signatures, and information-theoretic anomalies. His specific proposal that extraterrestrial artifacts might be found in the solar system’s stable orbital positions or even encoded in terrestrial biology has been cited in multiple subsequent SETA papers.
Oumuamua and IM1 as SETA Candidates
The Avi Loeb piece in this library documents the most recent and most institutionally significant engagement with the SETA hypothesis, though Loeb’s work on Oumuamua and IM1 is typically framed in terms of the interstellar visitor hypothesis rather than the surveillance probe hypothesis.
The distinction is important. Benford’s co-orbital surveillance hypothesis proposes that probes would be placed in stable long-duration orbits within the solar system, remaining in the vicinity of Earth for extended periods. Loeb’s interstellar visitor hypothesis proposes that specific objects whose trajectories establish their origin outside the solar system, specifically Oumuamua and IM1, might be probes traveling through the solar system rather than stationed within it.
Whether an advanced civilization conducting surveillance of Earth would deploy stationary orbiters, as Benford’s hypothesis describes, or transit probes that pass through the inner solar system on flyby trajectories, as Loeb’s hypothesis describes for Oumuamua, or both simultaneously, is a question that the available evidence cannot distinguish between. Both hypotheses are physically coherent and both are consistent with the available evidence within their specific frameworks.
The Galileo Project that Loeb founded at Harvard represents the most rigorously institutionalized current SETA program, applying calibrated instruments and peer-reviewed methodology to systematic monitoring of anomalous aerial and interstellar phenomena. Its specific relevance to Benford’s co-orbital hypothesis is that its all-sky camera network, once fully deployed, will provide continuous monitoring of the sky that is capable of detecting anomalous objects in Earth’s vicinity, including potential co-orbital objects that transit the observable sky.
The specific convergence of Benford’s co-orbital survey proposal and Loeb’s Galileo Project’s systematic monitoring program represents the two ends of a coordinated SETA research strategy: Benford proposes searching the known co-orbital population for physically anomalous objects, and Loeb proposes monitoring the sky continuously for anomalous transient phenomena. Together they provide coverage of both the long-duration stationary probe scenario and the transit probe scenario.
What the Absence of Detection Means
The fifty-year null result of SETI and the much shorter but equally null result of the formal SETA surveys conducted to date carry different information about the probability of extraterrestrial intelligence than they are typically presented as carrying.
The SETI null result is typically presented as negative evidence for extraterrestrial civilizations: if they existed and were transmitting, we would have detected signals by now. This inference is much weaker than it appears, because it assumes that electromagnetic transmission is the primary mode of interstellar communication, that civilizations transmit at frequencies and power levels detectable by human technology, and that the survey coverage achieved in fifty years is sufficient to sample a significant fraction of the relevant parameter space. All three assumptions are contestable.
The SETA null result from the limited surveys conducted to date is weaker still: the surveys covered a tiny fraction of the potentially relevant orbital locations with technology that would miss any probe not brighter than approximately 17th magnitude. The Earth Trojan survey completed in 1983 with a 0.8-meter telescope at a single epoch is not a comprehensive survey of the co-orbital population by any current standard.
Benford’s specific point about the informational value of the search is the most useful framing: even a null result from a systematic modern survey of the co-orbital population with current instrument sensitivity would be genuinely informative, establishing that no probes with properties above the survey’s detection threshold are present in the surveyed locations. This is a tighter constraint than the current absence of search provides, which is simply the absence of constraint from an unsurveyed population.
The alternative, not searching the co-orbital population with modern instruments because a probe seems too unlikely to justify the telescope time, is a specific choice not to gather information that would be informative in both positive and negative results. Benford’s point that the search is cheap relative to its information value is the correct framing: the co-orbital survey is not an expensive program. It is a decision about whether to look at the specific locations where SETA theory predicts we would find evidence if it exists.
The Surveillance Hypothesis and the UAP Record
The co-orbital surveillance hypothesis raises a specific question that the UAP disclosure record documented in this library’s UAP cluster makes more interesting than the conventional SETI framing acknowledges.
If an extraterrestrial civilization has maintained surveillance of Earth from a co-orbital position over millions or billions of years, the specific detection of that civilization’s activity would not necessarily come from astronomical observation of the probe itself. It might come from observation of the probe’s operational behavior: the deployment of subsidiary observation platforms at lower altitudes, the retrieval of samples from Earth’s surface or ocean, or the monitoring of specific human activities that represented threshold events in the civilization’s development.
The UAP phenomena documented across this library’s cluster, objects demonstrating capabilities beyond current human technology, operating in military airspace, demonstrating specific interest in nuclear weapons facilities, and in some cases retrieved from impact sites for reverse engineering, are consistent with exactly this operational behavior from a long-duration surveillance platform in the co-orbital zone.
Whether the UAP phenomena represent the operational activity of a co-orbital surveillance probe, independent interstellar visitors, human black programs whose capabilities have been suppressed from the public record, or something else entirely, is the question that the convergence of Benford’s co-orbital hypothesis, Loeb’s interstellar visitor evidence, and the UAP disclosure record makes genuinely pressing.
The Stargate remote viewing piece in this library documents sessions in which trained viewers reported detecting non-human presences at non-terrestrial locations and reported that those presences detected the viewers’ attention. Whether the specific non-terrestrial locations targeted in those sessions correspond to the co-orbital positions that Benford’s hypothesis identifies as the most probable surveillance probe locations is a question that the partial release of the Stargate program’s archive does not permit answering from the available record.
The co-orbital population has not been systematically surveyed with modern instruments. The Earth Trojans are poorly catalogued. The L4 and L5 Lagrange points contain objects whose full inventory is not established.
Whatever is in those positions has been there since before any instrument capable of detecting it was built. The survey that would determine whether the positions are empty or occupied has not been conducted.
Benford’s proposal is on the table. The Vera Rubin Observatory is operational. The instruments exist.
The question is whether anyone with the authority to schedule the telescope time considers it worth asking.
