[Artist’s impression of the Palomar Observatory Sky Survey telescope searching the night sky; credit: Caltech/Palomar Observatory]
A team of researchers has published a rigorous critical evaluation of recent studies that claimed to have found evidence of artificial objects — so-called technosignatures — in photographic plates from the first-epoch Palomar Observatory Sky Survey (POSS1-E). The new paper, accepted for publication in the Publications of the Astronomical Society of Australia (PASA), systematically dismantles key statistical and methodological arguments used to support the extraordinary claim that unidentified features in these decades-old plates represent glinting artificial objects near Earth.
The paper, “Critical Evaluation of Studies Alleging Evidence for Technosignatures in the POSS1-E Photographic Plates” (arXiv:2601.21946), was authored by Wesley Andres Watters, Laura Domine, Sarah Little, Cameron Pratt, Kevin H. Knuth, and Matthew Szenher. It targets a series of studies led by Beatriz Villarroel and colleagues that analyzed digital scans of photographic plates captured by the Palomar Observatory in the pre-Sputnik era, before humanity began extensively populating Earth orbit with satellites.
The Original Claims Under Scrutiny
The Villarroel studies, published in 2024 and 2025, drew attention to three principal findings: a purported deficit of unidentified features within Earth’s shadow, the sporadic presence of linear clusters of such features, and a positive statistical correlation between the timing of feature observations and historical nuclear weapons tests as well as Unidentified Aerial Phenomena (UAP) sighting reports. The authors of those studies argued that these patterns were consistent with sunlight glinting off artificial objects in orbit around Earth — potentially satellites or other technology of extraterrestrial origin.
The claims generated widespread interest in both scientific and popular circles, as they touched on the long-standing search for technosignatures: any detectable sign of technology created by an extraterrestrial civilization. The search for technosignatures has traditionally focused on radio signals, Dyson spheres, and atmospheric pollutants on exoplanets, but the possibility of finding evidence in archival photographic plates represented a novel and potentially groundbreaking approach.
Systematic Methodological Failures
Watters and his co-authors examined the Villarroel claims using two previously published datasets closely related to those used in the original studies. Their analysis reveals a cascade of methodological problems that collectively undermine the reported findings.
The Earth Shadow Analysis. The most prominent claim — a statistically significant deficit of features within Earth’s shadow — relies on the assumption that background features are distributed in a spatially uniform-random pattern across each photographic plate. Watters et al. demonstrate that this assumption is false. After constructing the correct null distribution of feature count deviations from the actual background, they find no statistically significant deficit in the shadow. “For these datasets, the assumption of a spatially uniform-random background distribution of features, essential to the Earth shadow analysis, is shown to be false,” the authors write in their abstract.
The Nuclear Test Correlation. The reported correlation between the timing of feature observations and nuclear tests becomes statistically insignificant after properly normalizing by the relevant number of observation days. The apparent correlation, the team found, is almost entirely determined by the observation schedule of the Palomar telescope rather than any physical relationship to nuclear detonations. This finding highlights a classic statistical pitfall: when observation opportunities themselves are clustered in time, apparent correlations with external events can emerge spuriously.
Problematic Datasets. The critical evaluation uncovered important inconsistencies in how datasets were defined across the Villarroel studies. The datasets used contained unvalidated entries, including catalogue stars, scan artefacts, and plate defects. More than 95 percent of features in the primary dataset used for analysis had previously been flagged as matches to known catalog objects or digitization artifacts in a rigorously vetted reference dataset constructed by Solano et al. (2022) — yet that cleaner dataset was sidelined in the Villarroel analyses.
Spatial Artifacts. The team documented systematic spatial patterns in the feature distributions that point to instrumental or processing artifacts rather than real astronomical phenomena. These include a gradual increase in feature number density toward the corners and edges of plates, empty north-south strips spanning multiple plates, clusters and voids with geometric shapes, and amorphous clusters. Such patterns are hallmarks of digitization and plate-scanning artifacts, not of artificial objects in orbit.
Circular Reasoning. The authors highlight what they describe as a circular argument in the original studies: the results of an inferential analysis were leveraged to simultaneously justify conclusions about both the origin of the features and the validity of the measurements themselves.
Historical Context: The Difficulty of Archival Transient Searches
To contextualize their critique, Watters et al. review the decades-long literature of searches for optical transients in photographic plates corresponding to gamma-ray bursts (GRBs). Despite extensive work, researchers in that field were unable to make a confident identification of a GRB-associated optical transient in archival plates — underscoring the formidable challenges of working with historical astronomical data.
“The historical record of GRB searches in photographic plates serves as an instructive case study,” the authors note. “If decades of targeted searches could not confidently identify GRB optical counterparts — events we know occurred — claims of identifying artificial transients in the same plates demand extraordinary evidentiary standards.”
The Debate Continues
The Villarroel team has not taken the critique quietly. In a response paper (arXiv:2602.15171), Beatriz Villarroel, Alina Streblyanska, Stephen Bruehl, and Stefan Geier argue that Watters et al. conflate object-level validation with ensemble-level statistical inference and rely on an aggressively filtered subset of data that has been reduced twenty-fold in sample size, rendering it statistically underpowered for testing the Earth shadow deficit.
The response maintains that the principal findings of the original studies “are not invalidated by the analyses presented in Watters et al. (2026)” and questions whether the filtered subset used in the critique demonstrates any meaningful improvement in sample purity.
Broader Implications for SETI
The exchange highlights a fundamental tension in the search for extraterrestrial intelligence: how to balance the scientific imperative to explore provocative anomalies with the equally important requirement for rigorous statistical methodology. The Watters et al. paper does not argue that technosignature searches are illegitimate; rather, it demonstrates how easily subtle biases, dataset contamination, and inappropriate statistical assumptions can produce false patterns that superficially resemble genuine signals.
For the broader SETI community, the paper serves as a cautionary tale about the importance of dataset validation, proper null hypothesis testing, and the need for transparency in how candidate features are selected and filtered. As searches for technosignatures expand beyond radio astronomy into optical, infrared, and archival domains, the methodological standards established in fields like high-energy astrophysics will become increasingly relevant.
The paper is available on arXiv at https://arxiv.org/abs/2601.21946 and has been accepted for publication in the Publications of the Astronomical Society of Australia.