"Aligned, Multiple-transient Events in the First Palomar Sky Survey" and "Transients in the Palomar Observatory Sky Survey (POSS-I) may be associated with nuclear testing and reports of unidentified anomalous phenomena" are the names of two companion papers published in October 2025 in Publications of the Astronomical Society of the Pacific and Scientific Reports, respectively. The principal authors of the two papers were Beatriz Villarroel and Stephen Bruehl.
The authors of the two papers contended that their research indicated the potential presence of UFOs orbiting the Earth in the 1950s. Their conclusion was criticized by other scientists, and preprints of both papers were rejected from archiving by arXiv for lacking "sufficient or substantive scholarly research".
Background
In the 1950s, San Diego's Mount Palomar Observatory photographed the northern sky in small sections. Subsequent research observed that some features present in the Palomar survey did not appear in later surveys. The difference was generally attributed to faults in the Palomar Observatory's glass photographic plates.[1] In a 2021 paper, Beatriz Villarroel and several co-authors concluded the plate fault explanation for the Palomar artifacts was unlikely.[1] The paper's conclusion was rejected in a rejoinder paper by University of Edinburgh astronomers.[1]
Content
"Transients in the Palomar Observatory Sky Survey (POSS-I) may be associated with nuclear testing and reports of unidentified anomalous phenomena", published in Scientific Reports, and its companion paper, "Aligned, Multiple-transient Events in the First Palomar Sky Survey", published in Publications of the Astronomical Society of the Pacific, studied digital scans of the original Palomar photographic glass plates and determined that the frequency of the transients increased around the time of nuclear tests and purported civilian "UFO sightings".[1][2][3][4][5] In "Transients in the Palomar Observatory Sky Survey", the authors present arguments against several "prosaic explanations", such as plate defects, and advance two hypotheses to explain their findings: that of a "previously undocumented atmospheric phenomenon triggered by nuclear detonations" or that "nuclear weapons may attract UAP [UFOs]".[6] Of the two, the authors claim the first hypothesis is unlikely.[6]
Both papers were published in October 2025.[1][7][8]
Authors
"Transients in the Palomar Observatory Sky Survey" was authored by Beatriz Villarroel, an astronomer at the Nordic Institute for Theoretical Physics and by Stephen Bruehl, a psychologist at Vanderbilt University, Bruehl serving as corresponding author.[6][9][2] "Aligned, Multiple-transient Events in the First Palomar Sky Survey" was authored by Villarroel and Bruehl, Villarroel serving as corresponding author. They were joined by Enrique Solano, Hichem Guergouri, Alina Streblyanska, Vitaly M. Andruk, Lars Mattsson, Rudolf E. Bär, Jamal Mimouni, Stefan Geier, Alok C. Gupta, Vanessa Okororie, Khaoula Laggoune, Matthew E. Shultz, and Robert A. Freitas Jr.[10][11]
Reception
The two papers, principally authored by Beatriz Villarroel and Stephen Bruehl, were based on scans of images created by the Mount Palomar Observatory (pictured) in the 1950s.
The papers' conclusions were met with skepticism by the scientific community, and arXiv declined to archive preprints of either paper, asserting they lacked "sufficient or substantive scholarly research".[12][13]
Scientific American noted that there were many simpler explanations, and that this provided an opportunity for UFO skeptics and enthusiasts to see how extraordinary claims are scientifically tested.[12]Michael Wiescher suggested Villarroel, Bruehl, and their coauthors had actually been observing debris that resulted from earlier nuclear tests and that would give the appearances of "bursts of radiance" when seen through a telescope.[12]SETI's Eliot Gillum noted that Villarroel's results could be explained by meteors that flew directly towards the telescope's view, instead of perpendicular to it, resulting in the appearance of specks of light as opposed to streaks.[12]Sean M. Kirkpatrick stated the results were probably the result of either solar flare radiation or high-altitude balloons.[12]
Princeton University's Robert Lupton, a research astronomer, commented he was left unimpressed with the strength of the statistical analysis undertaken in Villarroel and Bruehl's research.[14]Nigel Hambly, who specializes in digitized optical sky surveys,[14] suggested that examining the actual plates—instead of digital copies as Villarroel and Bruehl did—might result in a different conclusion, and that "there's no shame in being wrong".[12]
Writing on his personal website, Adam Frank applauded the researchers' effort at peer review of the two papers, though cautioned that "getting your paper published in a peer-reviewed quality journal does not make it right".[15]
Other critics have noted that the 1950s were a "golden age" of UFO sightings and the results correlating the appearance of the artifacts with UFO reports could be attributed to observation bias.[16] The Center for UFO Studies maintains a historic database of UFO sightings (UFOCAT) which was used by Bruehl & Villarroel.[6]
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