On a crisp August morning in Copenhagen, a roomful of physicists gathered to discuss the latest cosmic puzzles, but none captured the imagination quite like the interstellar visitor known as 3I/ATLAS. Hurtling through our solar system at 58 kilometers per second, this enigmatic object has upended expectations, challenging everything scientists thought they knew about comets from beyond our star’s reach.
According to a series of papers and observations published in late August 2025, 3I/ATLAS is not just another icy wanderer. Spectroscopic data from the Very Large Telescope (VLT) in Chile revealed a striking anomaly: a plume of nickel gas, but without the accompanying iron that always appears in natural comets. As reported by Daily Mail and echoed by Harvard physicist Avi Loeb, this nickel-only signature is typically found in industrial production of nickel alloys—a process that, on Earth, is the domain of advanced technology, not nature. Loeb posed the question on many minds: “Is this anomaly another clue for a possible technological origin of 3I/ATLAS?”
The VLT data, as discussed in a new study by Chilean astrophysicists, showed that 3I/ATLAS is shedding nickel at a rate of about 5 grams per second at a distance of 2.8 astronomical units (AU) from the Sun. The rate rises dramatically as the object approaches the Sun, following a steep power-law relationship. Even more curious, the gas plume also contains cyanide (CN), released at about 20 grams per second, with an even steeper rise as it gets closer to our star. These emissions are not typical for natural comets, which generally release nickel and iron together—both forged in the fiery crucibles of supernovae. The absence of iron, paired with the presence of cyanide, has left scientists scratching their heads.
NASA’s SPHEREx space observatory and the James Webb Space Telescope have added to the intrigue. Their observations, conducted in August 2025, showed that the gas cloud around 3I/ATLAS is dominated by carbon dioxide—an astonishing 95%—with only 5% water vapor. This is a far cry from the water-rich comets that populate our solar system, which typically release water, carbon monoxide, and carbon dioxide in much more balanced proportions. As Loeb wrote in his blog, “These results add to the chemical anomalies implied by the SPHEREx space observatory and Webb space telescope [and] are very different from an expected water-rich comet.”
The mystery deepens when considering the object’s size. Radiation data at a wavelength of one micron collected by SPHEREx suggest that the nucleus of 3I/ATLAS could be as large as 46 kilometers in diameter—making it millions of times more massive than the previous interstellar visitor, comet 2I/Borisov. If the nucleus truly is that large, it should have a dense coma of dust reflecting sunlight, resulting in a prominent cometary tail. But Hubble Space Telescope images revealed no such tail, despite expectations. The object’s brightness, then, must come from either a massive, reflective core or some other, as yet unexplained, mechanism.
The trajectory of 3I/ATLAS adds yet another wrinkle. Using Monte Carlo simulations and the GalPot galactic potential model, researchers traced its path back over a billion years, estimating its age at 4.6 billion years and suggesting it originated in the thick disk of the Milky Way. Its hyperbolic orbit, with an eccentricity of 6.2, and alignment with the ecliptic plane of the planets suggest it was ejected from its home system by a gravitational encounter with a giant planet—yet the close alignment with our solar system’s plane has led some, like Loeb, to speculate about a “technological design.”
While the notion of an artificial or extraterrestrial origin is controversial—Oxford astronomer Chris Lintott dismissed Loeb’s theory as “nonsense on stilts”—the anomalies demand explanation. The chemical formation of nickel through the nickel carbonyl channel is extremely rare in comets, but a standard technique in industrial nickel refining. Could nature have found a way to mimic industry, or is something more extraordinary at play?
Not all scientists are convinced by the artificial hypothesis, pointing to possible natural explanations. One theory suggests that intense radiation exposure could have selectively evaporated water, leaving behind the CO2-rich, water-poor composition. Alternatively, internal structures within the object could have shielded water ice from solar heat, limiting its sublimation. Regardless of the cause, the absence of water gas is particularly puzzling because 3I/ATLAS was observed near the “water ice line,” where water sublimation is expected to be robust.
The story of 3I/ATLAS is also a story of scientific curiosity and debate. At a conference in Copenhagen, Loeb described the lively discussions sparked by these findings. Nobel laureate David Gross, present at the event, pressed for further investigation: “We should also observe 3I/ATLAS with radio telescopes for any technological radio transmission coming from it.” The suggestion was met with agreement, as radio observations could provide a definitive test for artificial activity.
The timing of 3I/ATLAS’s arrival is, perhaps, poetic. As Loeb noted, the first nuclear explosion on Earth occurred on July 16, 1945—almost exactly 80 years before these observations. If 3I/ATLAS originated from the inner edge of the Oort Cloud, it could have begun its journey around the time humanity first broadcast its presence into the cosmos. “This act might have triggered the visit,” Loeb mused, highlighting the tantalizing, if speculative, connection between Earth’s technological awakening and the arrival of this interstellar mystery.
On October 3, 2025, 3I/ATLAS will make its closest approach to Mars, passing within 29 million kilometers of the Red Planet. The HiRISE camera aboard the Mars Reconnaissance Orbiter will attempt to image the object at a resolution of 30 kilometers per pixel, potentially allowing scientists to distinguish between the nucleus and the surrounding coma. Such data could finally pin down the object’s true size and composition, bringing clarity to a debate that has captivated the astronomical community.
For now, 3I/ATLAS remains an enigma—a cosmic messenger from the depths of the galaxy, carrying secrets that defy easy explanation. Whether its peculiar chemistry is the product of unknown natural processes or something more remarkable, its passage through our solar system is a reminder of how much we have yet to learn about the universe—and perhaps, about ourselves.
