When the object now known as 3I/ATLAS was first spotted racing through the Solar System earlier this year, astronomers thought they were witnessing a familiar type of cosmic visitor: a comet, dusty and icy, tossed into our planetary neighborhood from deep space. But new observations have thrown that assumption into question—perhaps entirely out the window.
At first glance, 3I/ATLAS behaved like other interstellar interlopers before it, notably ʻOumuamua in 2017 and 2I/Borisov in 2019. It moved fast. It was inbound from beyond the Solar System. And like Borisov, it appeared to carry a gaseous envelope, a telltale sign of volatile ices warming under the Sun. But then came the data—specifically, the composition of the material it was emitting.
Using high-resolution spectroscopy from the Keck II telescope in Hawaii, a team of astronomers detected a compound that caught them by surprise: nickel tetracarbonyl (Ni(CO)₄). This molecule, a toxic and volatile organometallic gas, is well known to engineers. It’s used in industrial metallurgy, particularly in refining and plating processes. But in nature? It has never been seen—certainly not in space.
3I/ATLAS as seen by the Hubble Space Telescope’s Wide Field Camera on in July. Credit: NASA
The detection, recently detailed in a peer-reviewed preprint study by W.B. Hoogendam et al., presents a puzzle. The object is emitting roughly four grams of nickel per second, with no trace of iron—an unusual chemical signature that, to date, has not been recorded in any known comet.
An Unnatural Balance
In nearly all documented comets, nickel and iron occur together, a well-established fact backed by a 2021 study in Nature, which analyzed ultraviolet and optical spectra from dozens of comets, including distant ones. That study showed consistent Fe/Ni ratios across various types and orbital classes.
Infrared data from the James Webb Space Telescope reveals the thermal emission profile of 3I/ATLAS. The brightest area corresponds to high infrared activity, consistent with the release of volatile compounds. Credits: NASA/James Webb Space Telescope
Nickel tetracarbonyl is highly volatile—it vaporizes easily under moderate heating. That could explain why it’s being released at relatively low solar distances. But it doesn’t explain how the molecule formed in the first place. On Earth, producing Ni(CO)₄ requires highly specific industrial conditions: purified nickel metal, carbon monoxide gas, and carefully maintained pressures and temperatures. There’s no verified natural process in space known to replicate this.
While the research team from Keck suggested a natural mechanism might still be possible, no confirmed model has emerged. The exotic chemistry of 3I/ATLAS, they admit, may involve processes not previously observed in planetary science.
A Plume With No Tail
Complicating matters is the object’s physical behavior. Unlike typical comets, which grow long, luminous tails that stream away from the Sun, 3I/ATLAS doesn’t have one. Instead, it’s ejecting material toward the Sun—an inversion of what comet physics predicts. The stream is composed of carbon dioxide, water vapor, and trace amounts of cyanide and nickel, but again, no iron.
This behavior was first reported by The New York Post, quoting Harvard astrophysicist Avi Loeb, who said the data resembles something more engineered than natural. “Why are we seeing a jet pointed at the Sun?” Loeb asked. “This was never observed for any other object.”
Spectral data from the Keck Cosmic Web Imager (KCWI) showing a concentrated plume directed sunward—a striking contrast to the classic comet tail, which always points away from the Sun. Credit: W. B. Hoogendam et al. 2025
This directional plume and strange composition have drawn comparisons to ʻOumuamua, another interstellar mystery that Loeb controversially suggested may have been artificially constructed. While most scientists reject that idea, 3I/ATLAS is raising similar questions—and at the very least, highlighting major gaps in our understanding of what interstellar debris can look like.
Mars Flyby and Missing Images
From October 4 to 7, 3I/ATLAS passed within 12 million miles of Mars, providing an extraordinary opportunity for observation. NASA’s Mars Reconnaissance Orbiter used its HiRISE camera to capture the object at unprecedented resolution.
Yet, due to a U.S. government shutdown, the images have not been released—a delay that’s frustrated scientists and space enthusiasts alike. In the New York Post interview, Loeb voiced his impatience: “We don’t need polished press releases. We need raw data.”
Other observatories have also targeted 3I/ATLAS. According to the original arXiv paper, the research team relied heavily on data from the Keck Cosmic Web Imager (KCWI). Their spectral analysis detected clear signatures of CN (cyanogen) and nickel tetracarbonyl, but not a hint of Fe I lines—again breaking with cometary norms. Supporting observations by the James Webb Space Telescope (JWST) and Hubble’s Wide Field Camera 3 have added to the picture, but the full datasets are still under review.
New Data, New Questions
If the compound and its origin are confirmed, 3I/ATLAS could become the first celestial object known to produce an exclusively human-made metal compound. The implications reach beyond cometary science. They touch on fields as wide-ranging as astrochemistry, planet formation, and even the search for extraterrestrial technology.
To be clear, no one is claiming the object is alien in origin. The majority of researchers remain firmly grounded in natural models, even if those models require speculative chemistry. Yet, as the paper’s authors note, the absence of iron and the presence of a volatile industrial compound remain unresolved.
References
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