Loeb’s fifteen claimed anomalies of 3I/ATLAS

By mid December 2025, as 3I/ATLAS swept past Earth on its way toward Jupiter, Avi Loeb, Harvard Professor and FOunder of Project Galileon, tried to put a bow on months of blog posts, talks and interviews. In a Medium essay titled “3I/ATLAS Maintained a Sunward Jet After Its Gravitational Deflection by 16 Degrees at Perihelion,” he assembled what he called fifteen “anomalies” that, in his view, keep an artificial origin for the object on the table. (Medium)

He grouped them into three clusters: geometric coincidences in the orbit and jet geometry, strange chemistry, and unusual physical behavior. Below is a narrative summary of those fifteen points, following his own numbering but translated into plain language and placing them in the broader scientific context.

Geometric coincidences: how 3I/ATLAS threads the Solar System

1. Retrograde orbit almost in the planetary plane
   Most comets that visit the inner Solar System move in or near the ecliptic, which is the flat plane defined by the orbits of the planets. 3I/ATLAS is unusual because it is on a retrograde path, so it travels the “wrong way” relative to planetary motion, yet its orbital plane is still within about 5 degrees of the ecliptic. Loeb assigns this configuration a probability of roughly 0.2 percent and takes it as a hint that the trajectory might have been deliberately chosen rather than drawn randomly from interstellar space. (Medium)
   Critics counter that this is an example of “after the fact” probability making. Many different orbital orientations would have looked “interesting” once noticed, and survey telescopes are naturally more sensitive to objects near the ecliptic, which boosts the chance that a new interstellar object we actually find will lie close to that plane. (Penn State Sites)
2. Close passes by Mars and Jupiter, but not Earth
   The second anomaly is about timing and geometry. Loeb notes that the object’s path brings it tens of millions of kilometers from Mars and Jupiter while keeping it well away from Earth, and that at perihelion it was on the far side of the Sun and therefore essentially unobservable from terrestrial telescopes. He treats this pattern as “fine tuning” and suggests that a technological craft might wish to avoid flying close to a noisy, radar‑rich planet like Earth while still sampling other worlds. (Medium)
   Mainstream orbital dynamicists see the same geometry as a natural outcome of a random hyperbolic orbit that happens to cut through the inner Solar System. Given the enormous volume of space and the long look‑back time to when the object entered the system, there are many ways to draw “suspicious” lines between its path and the planets after the fact. (NASA Science)

3. Perijove distance and Jupiter’s Hill sphere “match”
   In March 2026, 3I/ATLAS will pass Jupiter at about 53.5 million kilometers, which is almost identical to Jupiter’s Hill radius, the zone where Jupiter’s gravity dominates over the Sun’s. Loeb notes that this distance matches to within observational uncertainties and builds a scenario where the object might be using the encounter to release smaller devices into quasi stable orbits near Jupiter’s Lagrange points, places where a probe can “park” with minimal fuel. (Medium)
   Planetary scientists agree the match is numerically striking but remind readers that Hill radii exist for every planet. If one starts from the assumption “an alien probe would like to visit some dynamically special surface,” then almost any close pass can be reinterpreted as a hit.

4. A tightly collimated sunward anti‑tail
   Comets sometimes show “anti‑tails,” dust structures that appear to point toward the Sun because of perspective. In 3I/ATLAS, analysis of a Hubble image from July 2025 and later ground based images suggests a very narrow sunward structure that Loeb describes as at least ten times longer than it is wide and extending roughly a million kilometers. He argues that sustaining such a straight, sunward jet is hard to reconcile with ordinary ice sublimation and instead imagines a beam of particles or plasma that could shield a technological craft from the solar wind. (Medium)
   Polarimetric and imaging studies by independent teams instead interpret the feature as an unusual but natural dust jet in a low gravity environment whose particles are shaped and oriented by sunlight and the solar wind. (arXiv)

5. Rotation axis aligned with the Sun at entry
   Loeb cites modeling that places the rotation axis of 3I/ATLAS within about 8 degrees of the direction to the Sun when the object entered the inner Solar System. He calculates that the odds of such an alignment for a random spin axis are about 0.5 percent. In his narrative, this can be read as the object “presenting its face” to the star as it arrives. (Medium)
6. Jet anchored close to the sun‑facing pole
   Before perihelion, observers reported a wobbling jet that always stayed close to the sunward direction. Loeb interprets this as evidence that the base of the jet sits within roughly 8 degrees of the pole that faces the Sun. He assigns that configuration another 0.5 percent probability and treats the repeated alignment between jet, spin axis and Sun as additional geometric fine tuning. (Medium)
7. Mirror symmetry of the jet before and after perihelion
   After the comet swung around the Sun, a similarly narrow jet again appeared to point almost directly at the Sun, now from the opposite side of the nucleus relative to the direction of motion. Loeb frames this as a kind of geometrical choreography: before perihelion the jet appears sunward ahead of the object’s motion, and after perihelion an equally collimated structure points sunward but now trails the motion. He multiplies his earlier 0.5 percent factors and gets what he calls a “tiny” probability for this pattern to occur by chance. (Medium)
   In response, dynamical modelers like Jason Wright have pointed out that using several small a posteriori probabilities and multiplying them together is statistically suspect when the “anomalies” themselves were chosen after examining the data. (Penn State Sites)

8. Nightside activity and thermal insulation puzzle
   Loeb adds a thermodynamic twist. In his reading of the geometry, the regions on the nucleus that host the anti‑tail jet are sometimes on the nightside for months at a time. For a natural icy body, heat would tend to conduct around the interior and gradually warm those regions anyway, which should make it hard to keep jet sources “off” when they are dark and “on” only when they face the Sun. He argues that this pattern would be easier to explain if the jets came from engineered thrusters controlled by an onboard system rather than by passive heating. (Medium)
9. Deflection angle equals twice the jet opening angle
   As 3I/ATLAS rounded the Sun at perihelion, the Sun’s gravity bent its velocity vector by about 16 degrees. Loeb notes that this is almost exactly twice the measured opening angle of the narrow anti‑tail, about 8 degrees. For him, this symmetry is another coincidence: before perihelion one edge of the jet cone overlaps the sunward direction, and after perihelion the opposite edge can also align with the Sun, if the spin axis stays fixed in space. He treats the match between these angles as suggestive rather than definitive, but it still enters his “anomaly ledger”. (Medium)
10. Arrival direction near the “Wow!” signal
    The final geometric coincidence is more psychological than dynamical. Loeb notes that the incoming direction of 3I/ATLAS lies within about 9 degrees of the patch of sky from which the famous 1977 “Wow!” radio signal was detected. He gives that angular coincidence a probability of about 0.6 percent and hints that repeated activity from one region could be meaningful. (Medium)
    Radio astronomers point out that many other directions would also have seemed special: the galactic center, the anti‑center, bright nearby stars, or famous exoplanet systems. This is another classic example of what Josh Winn, in an email exchange that Loeb later published, calls the problem of “retrofitted” probability, where one only decides what counts as special after seeing the result. (Medium)

Composition anomalies: nickel rich gas and low water

11. Nickel without much iron
    Spectroscopic studies of 3I/ATLAS show emission lines from gaseous nickel and cyanide that are much stronger, relative to iron and to each other, than in thousands of previously catalogued comets, including the earlier interstellar visitor 2I/Borisov. (Medium) Loeb highlights this pattern and links it to an industrial “carbonyl” process used on Earth to produce nickel alloys, where nickel carbonyl gas is an intermediate. He argues that this chemical fingerprint has not been seen in natural comets and could hint at processing by technology, or at least at material that has passed through an engineered environment. (Medium)
    Planetary chemists accept that the nickel signal is striking but suggest that unusual primordial environments or selective outgassing from a heterogeneous nucleus could also produce odd elemental ratios, especially in an object that formed around another star. (arXiv)

12. Only about four percent water by mass in the plume
    Remote sensing of the gas and dust around 3I/ATLAS indicates that water makes up only a few percent of the outflowing material by mass, whereas in typical Solar System comets water is the dominant volatile. (Medium) Loeb interprets this as evidence that the comet’s activity may not be powered by ordinary ice sublimation, and suggests an alternative story in which sunlight is liberating thin surface layers of volatiles and dust that were picked up as a technological object moved through cold interstellar clouds. (Medium)

Unusual physical properties: size, polarization and color

13. Very massive, very fast, and allegedly too common
    Based on Hubble and other data, mainstream analyses place the nucleus of 3I/ATLAS somewhere in the range of a few hundred meters to several kilometers in size, with a total mass tens of millions of tons or more. (NASA Science) Loeb notes that this makes it roughly a million times more massive than ʻOumuamua and a thousand times more massive than 2I/Borisov, while also moving faster through the inner Solar System than either of those earlier interstellar visitors. In his own probability calculations he argues that, given current estimates of how much rocky material gets ejected into interstellar space, it is hard to randomly receive such a massive natural object once per decade, which again nudges him toward a “targeted” arrival story. (Medium)
14. Extreme negative polarization
    Polarimetry measures how light becomes polarized when it scatters off dust. A consortium led by Zuri Gray found that 3I/ATLAS shows an unusually deep and narrow negative polarization curve, with values that are outside the range previously seen in comets and asteroids. (arXiv) Loeb highlights this as one of his anomalies and notes that the effect could be connected to the strange anti‑tail geometry. In his framing it is another hint that the object may belong to a completely different category of material, potentially even a “Trojan horse” that hides engineered structures inside a natural shell. (Medium)
    The authors of the polarimetric study, however, interpret their own result as evidence that 3I/ATLAS extends the diversity of natural cometary materials rather than as a sign of technology. (arXiv)

15. Fast brightening and a very blue color near perihelion
    Near closest approach to the Sun, 3I/ATLAS brightened more steeply than most catalogued comets and showed a reflectance spectrum that is bluer than the Sun in visible light. (Medium) Loeb includes this as his fifteenth anomaly and, in earlier writing, has floated the idea that such behavior might signal that some sort of “engine” turned on at perihelion.

How to reads these “anomalies”

From a strict scientific standpoint, each item on Loeb’s list is either:

• A real and interesting measurement, such as the extreme negative polarization or unusual nickel abundances. (arXiv)
• A geometric or probabilistic pattern that looks special once pointed out, but that can be framed as a “coincidence” in different ways depending on what you decide to measure. (Medium)

NASA, ESA and multiple independent groups continue to treat 3I/ATLAS as a natural interstellar comet whose quirks expand our understanding of how other planetary systems eject icy bodies. (NASA Science) Their interpretation is that outgassing, dust dynamics and survey selection effects are enough to explain the observed behavior, including the non gravitational acceleration and the odd polarization curve.

Loeb’s own December 2025 follow up essay, “The 15 Anomalies of 3I/ATLAS: Should We Pay Attention to Them if They Were Not Forecasted?”, documents an email exchange with Princeton astrophysicist Josh Winn, who pushes back hard on the way these probabilities are constructed. Winn’s central point is that low “p‑values” assigned after you have already inspected the data cannot be treated as strong evidence that something is artificial, because one could always have chosen a different set of “surprising” features. (Medium)

From a UAPedia perspective, the anomaly list is important less as a proof that 3I/ATLAS is a craft and more as a window into Loeb’s approach. He is deliberately scanning interstellar visitors for any hint of techno signatures and refusing to assume that non‑human technology is off the table by default. That stance aligns with our editorial view that government and agency pronouncements, including from NASA, are valuable but not definitive, and that high quality outliers deserve sustained attention rather than reflexive dismissal. (NASA Science)

Whether future data and mission‑class observations of other interstellar objects confirm or erase these specific anomalies, the “fifteen” have already secured their place in the evolving story of how the astronomical community reacts when a truly strange visitor appears from the dark between the stars.

References

Gray, Z., Bagnulo, S., Borisov, G., Kwon, Y. G., Cellino, A., Kolokolova, L., … Muinonen, K. (2025). Extreme negative polarisation of new interstellar comet 3I/ATLAS (C/2025 N1). arXiv preprint arXiv:2509.05181. https://arxiv.org/abs/2509.05181?utm_source=https://uapedia.ai (arXiv)

Loeb, A. (2025, November 23). Anomalies of 3I/ATLAS, organized by likelihood. Medium. https://avi-loeb.medium.com/anomalies-of-3i-atlas-organized-by-likelihood-af20fb3b6d21?utm_source=https://uapedia.ai (Medium)

Loeb, A. (2025, December 17). 3I/ATLAS maintained a sunward jet after its gravitational deflection by 16 degrees at perihelion. Medium. https://avi-loeb.medium.com/3i-atlas-maintained-a-sunward-jet-after-its-gravitational-deflection-by-16-degrees-at-perihelion-e6810be9b3d8?utm_source=https://uapedia.ai (Medium)

Loeb, A. (2025, December 18). The 15 anomalies of 3I/ATLAS: Should we pay attention to them if they were not forecasted? Medium. https://avi-loeb.medium.com/the-15-anomalies-of-3i-atlas-should-we-pay-attention-to-them-if-they-were-not-forecasted-77375f9974d5?utm_source=https://uapedia.ai (Medium)

NASA. (2025). Comet 3I/ATLAS: Overview. NASA Solar System Exploration. https://science.nasa.gov/solar-system/comets/3i-atlas/?utm_source=https://uapedia.ai (NASA Science)

NASA. (2025). Comet 3I/ATLAS facts and FAQs. NASA Solar System Exploration. https://science.nasa.gov/solar-system/comets/3i-atlas/3i-atlas-facts-and-faqs/?utm_source=https://uapedia.ai (NASA Science)

Wright, J. T. (2025, November 9). Loeb’s 3I/ATLAS “anomalies” explained. AstroWright blog, Penn State. https://sites.psu.edu/astrowright/2025/11/09/loebs-3i-atlas-anomalies-explained/?utm_source=https://uapedia.ai (Penn State Sites)

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