Harvard astronomer Avi Loeb has argued at length that 3I/ATLAS — the third-ever interstellar object ever detected, currently screaming through the solar system at incredible speed — could be an enormous alien spacecraft measuring miles across.
While there’s a wide consensus in the scientific community that we’re looking at a comet largely made up of carbon dioxide ice, Loeb maintains that the object has many unusual properties that leave him suspicious it’s something even more exotic.
On his blog, Loeb outlines nine “anomalies” that he says support his eyebrow-raising hypothesis that we could be looking at an “alien mothership” that could be releasing “mini-drones” as it passes behind the Sun — despite admitting that the most likely explanation is that the 3I/ATLAS is simply a “comet of natural origin.”
1. Its Trajectory Is Closely Aligned With the Solar System’s Planets
Loeb points out that the mysterious visitor’s trajectory falls within just five degrees of the Earth’s path around the Sun, or the ecliptic plane. He argues there’s only a 0.2 percent likelihood of this happening.
2. It Visited Several Planets
In addition to its near alignment with the ecliptic plane, 3I/ATLAS’ arrival time takes it on a course right past Mars and Jupiter — both worlds that intrigue our own scientists in the search for life beyond Earth — in what Loeb calls a “remarkable fine-tuning of the object’s path.”
Earlier this month, the object passed by Mars closely enough for two of the European Space Agency’s spacecraft orbiting the Red Planet to snap photos of it. It’s expected to come within just 33.3 million miles of Jupiter in March 2026, which could allow NASA’s Juno spacecraft to intercept its path as well, Loeb argues.
3. It Grew an Anti-Tail
Astronomers have also observed 3I/ATLAS growing a second tail, which appears to point in the direction of the Sun.
Many other comets have been observed to have developed an “anti-tail,” in an optical illusion resulting from our relative positioning as it passes between the Earth and Sun. However, Loeb argues that 3I/ATLAS’s second tail is an outlier.
“This anomalous anti-tail, not a result of geometric perspective, had never been reported before for solar system comets,” Loeb wrote.
“The ice fragments evaporate after some time but because of the enhanced mass loss in the Sun-facing side, more of the bigger fragments can reach a large distance,” Loeb told Futurism in an email earlier this month.
4. It Appears to Be Enormous
According to Loeb’s calculations, the “diameter of its solid-density nucleus must be larger than [3.1 miles],” a measurement he inferred from an estimated mass of more than “33 billion tons.”
That would make it “three to five orders of magnitude” more massive than either ‘Oumuamua and 2I/Borisov, the only two other interstellar objects to have ever been observed careening through our solar system — which raises a confounding statistical question: why haven’t we observed way more smaller interstellar objects?
“Given the limited reservoir of heavy elements, we should have discovered on the order of a hundred thousand interstellar objects on the 0.1-kilometer scale of 1I/’Oumuamua before finding 3I/ATLAS, yet we only detected two interstellar objects previously,” he argued in a September blog post.
5. It’s Nickel-to-Iron Ratios Are Off the Charts
Scientists have found that 3I/ATLAS shows an “extreme abundance ratio” of nickel and iron in its gas plume, making it a major outlier when compared to 2I/Borisov and other more familiar solar system comets.
“At the distances at which comets are observed, the temperature is far too low to vaporize silicate, sulfide, and metallic grains that contain nickel and iron atoms,” an international team of astronomers wrote in a yet-to-be-peer-reviewed paper. “Therefore, the presence of nickel and iron atoms in cometary coma is extremely puzzling.”
Loeb argues that the findings could indicate the presence of “industrially-produced nickel alloys.”
6. Its Plume Is Mostly Carbon Dioxide Ice
Researchers have concluded, by examining data from the Spectro-Photometer for the History of the Universe, Epoch of Reionization and Ices Explorer (SPHEREx), that 3I/ATLAS’ coma surrounding its nucleus appears to be a mere four percent water by mass, bearing a much higher proportion of carbon dioxide gas than other comets.
While Loeb asserts that this makes the object an outlier, scientists have argued the opposite.
“SPHEREx’s finding very large amounts of vaporized carbon dioxide gas around 3I/ATLAS told us it could be like a normal solar system comet,” Johns Hopkins University astronomer Carey Lisse told Space.com last month.
In a separate preprint paper, an international team of researchers suggested that the object may contain “ices exposed to higher levels of radiation than Solar System comets,” or it could’ve “formed close to the CO2 ice line in its parent protoplanetary disk.”
7. It’s Extremely Negatively Polarized
The mysterious object has also shown “extreme negative polarization,” as detailed in a September paper, making it a major outlier.
“The combination of low inversion angle and extreme negative polarization is unprecedented among comets and asteroids, marking 3I/ATLAS the first object known with such polarimetric behavior and representing a previously unobserved population,” Loeb wrote in a blog post.
The findings suggest it has more in common with trans-Neptunian objects, minor planets, and other smaller objects orbiting the Sun beyond Neptune’s orbit, according to the authors of the September research paper.
8. It Could Be Behind the Famous “WOW! Signal”
Loeb has gone as far as to suggest that 3I/ATLAS may have emitted the “Wow! Signal,” a highly unsuual narrowband radio signal that was spotted by the Ohio State University’s Big Ear radio telescope in 1977. The signal led to widespread excitement about the possibility that it’d come from an extraterrestrial entity, and has remained a mystery for decades.
Loeb argues that “3I/ATLAS arrived from a direction coincident with the radio ‘Wow! Signal’ to within nine degrees, with a likelihood of 0.6 percent.”
9. It’s Much Bluer Than the Sun
Loeb initially only listed eight reasons he was suspicious of the 3I/ATLAS’ true nature. But this week, as 3I/ATLAS approaches its closest point to the Sun, or its perihelion, scientists observed a “rapid rise” in its brightness, appearing “distinctly bluer than the Sun,” Loeb wrote in a new blog post.
To the astronomer, it’s a “very surprising” finding. “Dust is expected to redden the scattered sunlight, and the surface of the object is expected to be an order of magnitude colder than the 5,800 degrees Kelvin at the photosphere of the Sun, resulting in it having a redder color than the Sun.”
“We must therefore add the blue color at perihelion as a ninth anomaly to the list of unexpected properties… of this strange interstellar object,” he wrote. “Does it employ a power source that is hotter than the Sun?”
If It Smells Like a Comet…
Whether these nine “anomalies” outlined by Loeb add up to make a convincing enough argument that 3I/ATLAS is “technological” in nature remains debatable.
NASA’s lead scientist for solar system small bodies, Tom Statler, told The Guardian last month that there’s plenty of evidence we’re simply looking at a rare visitor in the form of a natural comet from another star system.
“It looks like a comet,” he said. “It does comet things. It very, very strongly resembles, in just about every way, the comets that we know.”
“It’s a comet,” Statler concluded at the time.
Meanwhile, Loeb argued on his blog that “we have to collect as much data as possible to figure out the nature of this anomalous object.”
“The implication of alien technology would be huge and therefore we must take this possibility seriously,” he added. “Our biggest rocket, [SpaceX’s] Starship, is a hundred times smaller than 3I/ATLAS, so in case 3I/ATLAS were technological — its senders would have mastered capabilities that go well beyond our technologies.”
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