For generations, UFO enthusiasts have longed for claims of aliens visiting Earth to be seriously investigated by scientists. Now they are getting their wish. This month prominent peer-reviewed journals have published two papers that link apparent flashes of light seen by a telescope 70 years ago to potential artificial objects in space. But there are many simpler explanations, providing an opportunity for UFO enthusiasts to see how extraordinary claims are tested—and often undone—by ordinary science.
“I think there are many in the UFO community who really want to know what’s going on,” says Adam Frank, an astrophysicist at the University of Rochester, who has written frequently about the prospects of alien life. “I think it is worthwhile for us to have these open, transparent investigations. This is a great way to show people how science works.”
Beatriz Villarroel, an astronomer and theoretical physicist at the Nordic Institute for Theoretical Physics in Sweden, is the driving force behind both papers. The first was published in the Nature journal Scientific Reports on October 20, after a six-month peer review process, and the second was published in the Publications of the Astronomical Society of the Pacific on October 17, after a shorter review process. Both concern data gathered at the Palomar Observatory in California from 1949 to 1958 for a project called the Palomar Sky Survey, which was one of the first detailed astronomical surveys of the sky.
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About 2,000 photographic plates were used as part of the survey. Each was a glass sheet coated in an emulsion, or a layer of chemicals, that reacted to incoming light, mostly from stars across the sky. This was the main method of recording astronomical images before the advent of digital cameras. Each photographic plate was the size of a vinyl record cover and was physically lifted into and removed from the telescope that conducted the survey, the 1.2-meter Palomar Schmidt telescope, later renamed the Samuel Oschin Telescope. The plates were digitized in the 1990s and 2000s.
Villarroel and her team used the digitized scans to study the night sky as it was before the 1957 launch of the first artificial satellite, the Soviet Union’s Sputnik 1, to eliminate the possibility of seeing space-based interference from human activity. They used image processing software to look for transients—short-lived celestial events, such as stars flaring in brightness or fading from view, that are often associated with extreme astrophysics. Under the auspices of Villarroel’s Vanishing & Appearing Sources during a Century of Observations (VASCO) project, they identified more than 107,000 transients.
In principle, besides fluctuating stars transients can be associated with other things, too, such as extreme space weather events impinging on the upper atmosphere, sunlight glinting off reflective objects near Earth, as well as flaws in the telescope or the imaging process. Among the events that the researchers identified, they noted several examples where multiple transients appeared aligned in a straight line across a single photographic plate, a configuration that Villarroel argues is unlikely to occur by any known natural phenomenon. (Other experts, such as Princeton University astrophysicist Robert Lupton, say that finding several such patterns in thousands of star-spangled plates could easily be mere coincidence.)
In the Scientific Reports paper, Villarroel and Stephen Bruehl, a Vanderbilt University Medical Center anesthesiologist with an interest in UFOs, found that many of the transients occurred on or near dates of nuclear testing, with multiple nuclear test sites known to be near the Palomar Observatory at the time. They wrote that transients appeared to be 45 percent more likely on dates within 24 hours of a nuclear test. “On days when there was no nuclear test, you saw transients on 11 percent of those days,” says Bruehl, the paper’s lead author. “On the day after a nuclear test, you saw transients on almost 19 percent of those days.” From the 2,718 days of observations made by the Palomar Sky Survey, Villarroel’s team identified transients occurring on 310 days, with the most being 4,528 transients in one day.
In their paper, Bruehl and Villarroel linked these transients to global reports of UFO sightings and found a small association, with transients being identified on the same day as a UFO, or UAP (unidentified anomalous phenomenon), sighting. They claimed an 8.5 percent increase in the number of transients identified on days with UAP reports and suggested this might mean the two were linked, referencing “a well-known strand of UAP lore suggesting that nuclear weapons may attract UAP” to observe the events.
A candidate transient is highlighted (blue circles) in this figure from an associated paper by Beatriz Villarroel and colleagues. Derived from digital scans of photographic plates from the Palomar Sky Survey and color-inverted to emphasize detail, these images show what the authors say could be flashes of light from artificial objects in outer space, years before humans sent spacecraft into Earth orbit.
“Aligned, Multiple-Transient Events in the First Palomar Sky Survey,” by Beatriz Villarroel et al., in Publications of the Astronomical Society of the Pacific, Vol. 137; October 2025 (CC BY 4.0)
The link to nuclear weapons can be simpler, says Michael Wiescher, a nuclear astrophysicist at the University of Notre Dame in France. “Nuclear tests obviously have an impact on the atmosphere,” he says. For example, the first telecommunications satellite, NASA’s Telstar 1, was knocked out by an electromagnetic pulse from the American high-altitude nuclear test Starfish Prime in November 1962. Nuclear tests can also leave “a lot of junk in the outer atmosphere,” Wiescher says, such as bits of metal and radioactive dust, that could appear briefly as starlike bursts of radiance to a telescope.
In their Publications of the Astronomical Society of the Pacific paper, Villarroel and her team suggested that the number of transients dropped by about 30 percent in regions of the overhead sky that would have fallen within Earth’s umbral shadow, directly in line with the sun. This pattern could be explained if the transients were caused by sunlight-reflecting objects that were orbiting Earth, they wrote. “It looks like we are dealing with something that looks pretty artificial in a time when there shouldn’t be anything there,” Villarroel says.
Each photographic plate took a 50-minute exposure of the sky, leading Villarroel to suggest that these putative objects were stationary in space, possibly in geostationary orbit some 22,000 miles (35,000 kilometers) above Earth. Bright objects in lower orbits—or other less sensational possibilities such as meteors—would have left a streak instead of a starlike dot of light, she says.
Frank says that the two papers are a chance for scientists to have something tangible to scrutinize regarding UFOs. Often, he says, evidence has been little more than “fuzzy blob photos” or hearsay. “What’s interesting about these two papers is: they played by the rules by which science can evaluate evidence,” he adds, referencing Carl Sagan’s famous adage that “extraordinary claims require extraordinary evidence.”
Whether there is “extraordinary evidence” here is up for some debate. The papers were not accepted by arXiv.org, an online preprint server where nonpaywalled scientific papers are often uploaded, with the website noting to Villarroel that the Scientific Reports paper in particular “does not contain sufficient or substantive scholarly research.”
There are also a host of simpler explanations for Villaroel’s transients—which have drawn previous scrutiny from skeptical astronomers—that don’t require the extraordinary claim of UFOs. Sean Kirkpatrick, who was head of the Pentagon’s UFO-investigating All-Domain Anomaly Resolution Office (AARO) from July 2022 to December 2023, says he thinks the link to nuclear testing and Earth’s shadow is key. “Taken together, that tells me that these transients have both a solar and nuclear overlap,” he says. “The first thing that comes to mind is solar flare radiation or ionized particle radiation from nuclear testing,” split-second bursts of light in the upper atmosphere that would manifest as a point source rather than a streak. Another possible explanation is high-altitude balloons, which were used to do nuclear monitoring. “You’re going to have a lot of those around nuclear testing, and so if people see them, a lot of people are going to report them,” he says.
Kirkpatrick says Villarroel and her team could use today’s geostationary satellites to see if they could reproduce the transients seen by Palomar, building a replica photographic plate and determining if it produces similar transients from known orbiting objects. “What they have not done is prove this technique works on today’s geostationary objects,” he says. If it does, that could open the avenue to other non-UAP explanations to explore, such as pieces of sunlight-catching ice or rock lingering in trapped orbits far above Earth. “There are things that get captured up there and just kind of float around,” Kirkpatrick says.
There are astronomical explanations, too, Lupton says, because “things go bang and vary all over the place.” He points to the example of gamma-ray bursts, extremely bright cosmic explosions that were discovered serendipitously by nuclear-monitoring satellites in the 1960s. “We were trying to see if the Russians were [secretly] blowing up nuclear weapons, and it turned out to be stars destroying themselves on the other side of the universe,” he says. The Vera C. Rubin Telescope in Chile is expected to find millions of transients from supernovae—exploding stars—alone, among many other types of transients, when it begins a 10-year survey of the sky later this year.
The most prosaic explanation is that Villarroel’s transients are simply artifacts in the photographic plates such as speckles of dust, blobs in the emulsion or even radioactive particles. Nigel Hambly, an astronomer at the University of Edinburgh, who has previously analyzed Villarroel’s work and who has extensive experience with photographic plates from Palomar and other observatories, says one way to check would be to study the original plates themselves rather than using digital copies. “I’ve been caught out many times by apparently real things turning up in my data,” he says, especially when working with plates that weren’t stored in pristine conditions. “When you actually physically examine the plates under a microscope, you begin to get a feeling for what’s real and what’s spurious,” he says. “There’s no shame in being wrong.”
Eliot Gillum, director of optical SETI (search for extraterrestrial intelligence) at the SETI Institute in California, says that whatever the transients really are, it will be interesting to apply the scientific process to them. “It’s wonderful to take a set of phenomena we don’t understand and study them,” he says. He adds that Villarroel and her team could test their same methodology on other photographic plate archives to see if the transients show up elsewhere. “There are plenty of other sets of digitized plates,” Gillum says. “It’s quite possible that there are multiple causes here. It would be great to figure them out.” He says that another possibility could be meteors that flew straight down into the telescope’s view rather than across it; that would make the objects appear as dots of light instead of streaks.
Villarroel says that she welcomes alternative ideas for what these transients might be. “Even if this turns out to be some new physical phenomenon, that’s super exciting,” she says. “That would mean we have discovered something new that nobody knew existed.” If that does turn out to be the case, there are plenty of other searches for extraterrestrials—such as NASA’s upcoming Habitable Worlds Observatory—that can whet the appetite of those longing for signs of life elsewhere in the cosmos.
“It’s one of the most important scientific questions that we have,” Frank says. “The great thing is: we now finally have the capacity to start answering this.”
