The 15 Anomalies of 3I/ATLAS: Should We Pay Attention to Them if They Were Not Forecasted?

[Avi Loeb Medium]

Image of the interstellar object 3I/ATLAS (top left panel) from a 0.25-meter telescope in Calabria, Italy, taken on December 15, 2025 at 1:58 UTC with 1.38 arcseconds per pixel — corresponding to 3,850 kilometers at the source distance. The other three panels show a brightness map at different wavelength bands centered on 0.658 [R], 0.53 (Green) and 0.445 (Blue) micrometers, using a Larson-Sekanina gradient filter. Their field of view spans 1.6 by 0.7 million kilometers and shows a prominent tightly-collimated anti-tail jet from 3I/ATLAS in the sunward direction, towards the bottom left corner. (Image credit: Toni Scarmato)

My latest essay, available here, listed 15 anomalies of the interstellar object 3I/ATLAS. The following morning before my routine jog at sunrise, I had the following exchange with my esteemed colleague, the astrophysics Professor Josh Winn from Princeton University. He wrote:

“Dear Avi,

I’ve been following this story, and your interpretations, with interest and enjoyment. But there has been something bothering me and I finally feel moved to write you about it.

To my knowledge, none of the anomalies were predicted, and hence, I cannot take seriously the very low probabilities that have been assigned to them. For example, it is interesting that the trajectory is nearly anti-aligned with the ecliptic, but it also would have been interesting if the orbital plane had been aligned, perpendicular to, exactly 45° from, …, the ecliptic. Or aligned with the Sun’s equatorial plane, or Pluto’s orbit, or Halley’s Comet … Or if the trajectory had pointed back to a known star, or the galactic center, or the anti-center, or the galactic poles, or the LMC, etc. It is interesting that the trajectory makes close passes to a few planets but not Earth, but it also would have been interesting if the trajectory made close passes to any subset of planets, or only to the Earth, or if it avoided any close approaches with planets despite being near the ecliptic.

This problem is avoided if predictions are made in advance. Can we make definite predictions for the future behavior of the object under the hypothesis that it is technological?

Did anyone predict that coming close to a planet’s Hill radius would be a sign of technological origin? Or that the nickel/iron ratio would be unusual? That jets would emerge in special directions? I remember reading about a prediction that the object would perform a certain maneuver near perihelion — can that be ruled out?

Noticing anomalies is obviously important, but without trying to make and test predictions, there is something important missing.

Best wishes,

Josh”

My reply was as follows:

“Dear Josh,

A predictable anomaly is an oxymoron, a contradiction in terms. The nature of an anomaly is that it is unexpected, an outlier. Quantum mechanics stemmed from anomalies of classical physics. And even after it was discovered, Albert Einstein insisted that quantum mechanics cannot have `spooky action at a distance’. When discovering new knowledge, we should not assume that our imagination is good enough to forecast this knowledge. When I started astrophysics 38 years ago, the possible existence of hot Jupiters was definitely not forecasted or included as a target to search for in the folklore of observers.

Regarding my list of anomalies for 3I/ATLAS: the existence of nickel without iron is a result of the carbonyl pathway for the industrial production of nickel alloys. We have never seen it in comets so it is an anomaly. It is a technological signature in the same way that artificial light on the nightside of an exoplanet would be.

When detectives arrive at the scene of a crime, your methodology would ask them to ignore unusual facts because they did not forecast them before arriving there. I say that this is the wrong approach to crack the mystery of the crime, and any practicing detective — including fictional ones like Sherlock Holmes, would have agreed with me.

Happy Hannukah!

Avi”

Josh replied promptly:

“Thanks, Avi, for taking the time to reply — and Happy Hannukah!

I agree that it’s very important to notice anomalies and take them seriously. My point was that to convince oneself and other people of a hypothesis, one needs to go further — one must use the anomalies to construct theories that make predictions that are then confirmed.

A problem with the hypothesis that 3I/ATLAS is of technological origin is that it is very flexible, because of the unknown goals and technologies involved, and can therefore be retrospectively considered compatible with just about any anomaly.

I’d like to see some predictions that can be tested, and likewise, a list of possible observations that would rule out the possibility that 3I/ATLAS is of technological origin. Think about how the situation would differ if you’d written a paper a year ago with rational arguments that technological visitors would likely arrive on retrograde orbits and come to perihelion at solar opposition!

Relatedly, I think the “a posteriori” probabilities that you refer to in various messages are misleading, because the statistical questions are constructed after already knowing the observations. The probability of interest is not “how likely is it that a random trajectory would be so close to retrograde” — rather, it is “how likely is it that a random trajectory will have any combination of parameters that can be regarded retrospectively as interesting”? The latter probability is difficult to calculate but is probably high. It’s like picking a random integer and then afterward trying to see if there’s anything interesting about it … it’s almost always possible to find something interesting (see, e.g., https://mathigon.org/almanac)

If you disagree, would you like to make a bet with an odds ratio of (0.2%) * (0.5%) * (0.5%)² = 0.00000000025, the product of probabilities cited in your recent message, that the object will turn out to be of technological origin? That is, if it is of technological origin, I pay you $1, and if it is not of technological origin, you pay me $4 billion? I’ll lower the payout to $1 billion to make it even more enticing.

Josh”

In concluding our exchange, I wrote:

“What you’d like to see in terms of a prediction is irrelevant as to the question of whether a conjecture is real. The fact that hot Jupiters were not predicted does not mean that the anomalies they represented in the minds of traditional thinkers were not real just because they were not predicted ahead of time. There is a sense of arrogance in the way you formulate the idea that we should predict or expect new knowledge. In fact, the most exciting aspect of science is the unknown unknowns, even though we usually fund projects that search for the known unknowns. The foundation of science is the humility to learn, not the arrogance of expertise.

I am not claiming that 3I/ATLAS is technological but only stating that we should consider its anomalies with this possibility in mind.”

Interestingly, the Chronicle of Higher Education published here a couple of days ago an article by Sally Satel titled: “Are Bad Researchers Bad People: The absence of humility, integrity and open-mindedness isn’t just a moral failure. It’s a methodological one.” The opening sentence of the article states:

“Charles Darwin set a “golden rule” for his study of nature. Whenever he encountered information that ran counter to his ideas, he would make a note of it “without fail and at once.” Why? Because, as Darwin wrote in his autobiography, “such facts and thoughts were far more apt to escape from the memory than favourable ones.”

In another passage, Sally writes: “In addition to epistemic humility, other virtues, as…, Intellectual Virtues, include open-mindedness, love of knowledge, and generosity (sharing intellectual goods), alongside such traits as ‘intellectual courage’ (willingness to consider difficult, unpopular, or counterintuitive ideas) and ‘intellectual firmness’ (the ability to balance one’s belief against letting go in the face of compelling evidence).”

I rest my case, Josh.

ABOUT THE AUTHOR

(Image Credit: Chris Michel, National Academy of Sciences, 2023)

Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011–2020). He is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. The paperback edition of his new book, titled “Interstellar”, was published in August 2024.

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