Overview
On July 1, 2025, a survey telescope in Río Hurtado, Chile — part of NASA's Asteroid Terrestrial-impact Last Alert System, or ATLAS — flagged a fast-moving point of light and reported it to the Minor Planet Center. Within days the orbit calculations settled the essential fact: the object was not bound to the Sun. It was passing through. Designated 3I/ATLAS, it became only the third interstellar visitor ever recorded, after 1I/ʻOumuamua in 2017 and 2I/Borisov in 2019, and at roughly 210,000 kilometers per hour it was the fastest thing anyone had clocked crossing the solar system.
Astronomers called it a comet. A sizable portion of the internet called it something else. Over the months that followed, a theory took shape that 3I/ATLAS was an alien spacecraft — a "mothership," in the most durable framing — steering itself through the planets, perhaps releasing probes, perhaps hiding its true nature behind a veil of cometary dust. When the University of Washington's Center for an Informed Public tallied the conversation in December 2025, it counted roughly 700,000 posts about the object on X between discovery and late November. About 280,000 of them — four in ten — invoked aliens or extraterrestrial technology.
The theory did not bubble up from anonymous forums alone. A significant share of it traced back to Harvard.
The Professor and the Preprint
Avi Loeb, the Harvard astrophysicist who years earlier argued that ʻOumuamua deserved consideration as a possible artifact, began raising the same question about 3I/ATLAS almost immediately. On July 26, 2025, the New York Post ran a story on a preprint Loeb had co-authored with Adam Hibberd and Adam Crowl exploring the artificial-origin hypothesis. The Center for an Informed Public found that before that story, the alien frame was absent from the top posts about the object; afterward, it never left.
The case assembled itself from a catalog of claimed anomalies. The object's size — "on the order of the width of Manhattan" — drew about 44,000 posts. Its trajectory, described as suspiciously fine-tuned to pass near multiple planets, drew around 100,000. Its non-gravitational acceleration, which some posts said "might be produced by an engine," fed roughly 87,000 more. Spectroscopy showing nickel vapor without the iron that normally accompanies it was read as the signature of industrial alloy production — the sort of thing a shipyard would leave behind, the argument went, not a dirty snowball. Jets from the nucleus became thrusters. Fragments became mini-probes. Some 60,000 posts connected the comet to the 1977 "Wow!" signal on the grounds of an alignment in the sky.
Loeb himself was named in about 130,000 posts, and 63 percent of those paired him directly with the alien hypothesis. The Seattle researchers summarized the dynamic in a single line: a scientist's speculation is somebody else's conspiracy theory. Loeb's caveats tended to fall away in transit.
The September Panic
A harder-edged strand emerged in the fall. A September 29 New York Post article went viral, and within days social feeds carried claims that the comet was on a collision course with Earth, that militaries were quietly convening, that secret missions to divert the object were underway. One widely shared post attributed a warning about "hostile reconnaissance" to physicist Michio Kaku; the accompanying image came from an interview he had given on February 20, 2025 — months before the comet existed in any catalog. Al Jazeera examined the collision rumors on October 3 and quoted NASA saying the comet "poses no danger to Earth," with its closest approach around 270 million kilometers away; ESA said the same. A companion claim that NASA had "activated planetary defense" traced back, on inspection, to a routine astrometry training exercise.
The conversation peaked in late October. Loeb's appearance on Joe Rogan's podcast was announced on October 21, and the episode landed almost exactly at perihelion, when the comet swung within about 210 million kilometers of the Sun on October 30 — briefly unobservable behind it, which did nothing to calm anyone. The Center for an Informed Public logged roughly 30,000 anomaly posts in three days. When NASA released new images of the object on November 19, cover-up rumors followed within hours.
470,000 Signals
On December 18, 2025, as the comet made its closest pass by Earth, the Breakthrough Listen program pointed the Green Bank Telescope in West Virginia at it and listened across four radio bands. The scan flagged 470,000 candidate signals. All but nine were eliminated because they persisted when the telescope pointed elsewhere; the final nine were identified as human-made radio interference. "There is currently no evidence to suggest that these objects are anything other than natural astrophysical objects," the study authors wrote in results reported in 2026, while noting that such rare visitors warrant thorough checking. Two other teams ran independent searches at different frequencies and reported the same silence.
The James Webb Space Telescope had been watching too. A NASA Goddard team led by Martin Cordiner analyzed the comet's chemistry from Webb's December observations and found deuterium levels about thirty times those of solar system comets, alongside unusually low carbon-13 — a fingerprint, the researchers reported in 2026, of formation some ten to twelve billion years ago, in a cold corner of the galaxy during its era of peak star formation. If the measurement holds, 3I/ATLAS predates the Sun by billions of years.
The Ledger, Mid-2026
As of mid-2026 the object is receding from the Sun and will not return. Loeb has continued publishing on its anomalies, and his readers note that a null result across four radio bands is not a survey of every frequency an unfamiliar technology might use. Others point to the age study, the cometary outgassing, and the scans, and consider the file closed. NASA, for its part, keeps releasing archival observations from the flotilla of spacecraft that watched the flyby. Both audiences are reading the same data. They are not reading the same object.