Avi Loeb’s Extraterrestrial Theories on the Three Confirmed Interstellar Objects

Avi Loeb, the Harvard astrophysicist known for his provocative work on extraterrestrial intelligence, has indeed proposed “wild” alien hypotheses for all three confirmed interstellar objects (1I/’Oumuamua, 2I/Borisov, and 3I/ATLAS—also referred to as 2024 PT₅ or the third interstellar interloper). These ideas stem from anomalies like non-gravitational acceleration, unusual shapes or compositions, and trajectories that Loeb argues defy natural explanations without invoking advanced technology. His claims often prioritize the simplest hypothesis that fits the data, even if it involves intelligent design, and they’ve drawn sharp criticism from peers who favor naturalistic models (e.g., hydrogen outgassing or icy fragments). Below, I outline his key theories for each, highlighting the wildest elements with supporting evidence from his papers, books, and public statements.

1. 1I/’Oumuamua (Discovered 2017)Loeb’s most famous speculation centers on this cigar- or pancake-shaped object, which tumbled through our solar system without showing typical cometary dust or gas. In his 2021 book Extraterrestrial: The First Sign of Intelligent Life Beyond Earth and a 2018 paper co-authored with Shmuel Bialy, he argues ‘Oumuamua’s peculiarities—extreme elongation (up to 10:1 aspect ratio), non-gravitational acceleration (0.1% deviation from orbit), and lack of a coma—make it unlikely to be a natural body like a fractured asteroid or hydrogen iceberg. Instead, he posits it as alien technology, specifically a lightsail (a thin, reflective sheet propelled by stellar radiation pressure, akin to concepts in Breakthrough Starshot). The wildest twist: It could be a fully operational probe dispatched intentionally to Earth’s vicinity by an extraterrestrial civilization, possibly for reconnaissance, having traveled interstellar distances for billions of years before tumbling into dysfunction. Loeb estimates the odds of a natural origin at under 0.1% based on its brightness variations and speed, calling it a “wake-up call” for humanity to prepare for cosmic neighbors.

2. 2I/Borisov (Discovered 2019)Unlike ‘Oumuamua, this comet displayed a classic tail and coma, leading Loeb to concede it’s likely a natural interstellar comet in his writings (e.g., a 2022 paper on interstellar objects). However, he hasn’t shied from speculative ties to alien origins, grouping it with the others as potential “messengers” from distant systems. In a 2023 Medium post and interviews, Loeb highlights Borisov’s hyperbolic orbit (eccentricity ~3.36) and composition (high carbon monoxide) as consistent with an ejected body from another star, but he floats the wild idea that it could be part of a coordinated flotilla of probes, with ‘Oumuamua as a scout and Borisov as a “mothership” or backup craft from the same civilization—perhaps designed to seed or survey habitable zones. This builds on his broader framework in Extraterrestrial, where he suggests interstellar objects might carry microbial life or technosignatures, estimating a 50%+ chance of extraterrestrial intelligence in the Milky Way. The wildest element here is less direct (as Borisov fits cometary models better), but Loeb uses it to argue for urgent missions to intercept future visitors, implying hidden artificiality in its pristine, “shiny” state upon arrival.

3. 3I/ATLAS (Discovered 2024, Perihelion 2025)For this massive (~20-46 km diameter), fast-moving comet (velocity >60 km/s), Loeb has gone full throttle in 2025 blog posts and a preprint paper with Adam Hibberd and Adam Crowl. Anomalies include no visible water coma (only CO₂ and dust), a retrograde orbit aligned with inner planets, a nickel-rich plume (ratio defying known comets by <1% probability), and post-perihelion “non-gravitational acceleration” suggesting thrusters or an intact nucleus too large for natural survival. Loeb calculates its size makes it a 1-in-500 to 1-in-1,000,000 rarity if natural, implying design. His core theory: It’s alien technology, possibly a hostile probe navigating the solar system deliberately, with its trajectory allowing a secret thrust to orbit the Sun or target Earth. The wildest claims: An active engine “revving” for rapid escape (blue hue and anti-tail as exhaust), or a “Dark Forest” weapon per the Fermi Paradox resolution—sent to silently eliminate threats like humanity, potentially “obliterating a continent” on impact (though it’s safely passing 167 million miles away in December 2025). In a Fox News interview, he urged global preparedness, calling it a “pedagogical exercise” in astrodynamics but warning of existential risks.

Loeb’s overarching view, reiterated in his Galileo Project, is that these objects demand “space archaeology” to probe for artifacts, as natural explanations strain plausibility. Critics like Jason Wright dismiss them as unfalsifiable hype, but Loeb counters that ignoring them echoes historical scientific conservatism (e.g., rejecting meteorites). With more interlopers expected via telescopes like Vera Rubin, his theories keep fueling debate—substantiated by data fits but unsubstantiated by direct proof.

Avi Loeb looked at three random interstellar tourists and declared them all alien spacecraft. Turns out they were just rocks, comets, and more rocks.

So congrats, Avi: you’ve officially achieved a perfect 0-for-3 batting average, which means you’re not an astronomer anymore; you’re the guy who screams “UFO!” every time a pigeon flies past a streetlight. At this point, the only thing these objects have in common is that they all came from another star system just to get the hell away from your press releases.