The Tale of 3I/ATLAS and Sterile Neutrinos

[Avi Loeb Medium]

An image of 3I/Atlas on December 9, 2025 (left panel) shows a sunward jet (right panel, Larson-Sekanina gradient filter) that was also apparent in the Hubble Space Telescope image from November 30, 2025. (Image Credit: Toni Scarmato)

There is no doubt that we can learn something new from the interstellar object 3I/ATLAS, irrespective of whether it is an icy rock or a spacecraft. The only obstacle to learning is comet experts who display the arrogance of expertise. How can anyone claim to be an expert of interstellar objects when the sample size includes only two previously known examples, 1I/`Oumuamua and 2I/Borisov and when 3I/ATLAS displays 13 anomalies relative to these two (as listed here)?

The anti-tail of 3I/ATLAS appears in our highest-resolution images from the Hubble Space Telescope, one obtained before (here) and the second after (here) perihelion. The orientation of the anti-tail flipped relative to the direction of motion at perihelion and is definitely not a matter of perspective as is the case for some comets. What is the physics of the anti-tail of 3I/ATLAS?

Micrometer-scale, refractory dust particles would have been swept away from the Sun by the solar radiation and wind. The anti-tail must therefore contain something else. To account for its properties, I wrote three papers so far explaining it as being made of fragments of ice that evaporate before turning around (here and here) or large objects that are not affected much by the solar radiation or wind (here).

Why are comet experts and NASA officials so reluctant in displaying curiosity about the anti-tail or other anomalies of 3I/ATLAS?

To gain further insight, let us consider another news story that garnered attention over the past week. Two major experiments were motivated by anomalies in past data and searched for ghost neutrinos that do not couple to matter. They both failed to find these sterile neutrinos, as reported in two Nature magazine papers (here and here).

The Standard Model of particle physics lists three neutrino flavors of the electron, muon and tau types. Quantum-mechanical oscillations allow a neutrino of one flavor to be detected at a later time as a different flavor. Anomalies reported in previous experiments were inconsistent with this three-flavor picture and have motivated the hypothesis that an additional neutrino state exists of a sterile neutrino that does not interact with matter. The anomalous data included oscillations observed by the Liquid Scintillator Neutrino Detector (LSND) experiment and Mini-Booster Neutrino Experiment (MiniBooNE).

The first paper (here) from the MicroBooNE used oscillation data from two neutrino beams to exclude a single sterile neutrino interpretation of the LSND and MiniBooNE anomalies at the 95% confidence level. The second paper (here) used tritium beta-decay (electron emission) in the Karlsruhe Tritium Neutrino (KATRIN) experiment, to search for sterile neutrinos. A sterile-neutrino signal would appear as a distortion in the beta-decay energy spectrum, characterized by a discontinuity related to the sterile-neutrino mass. The analysis of the energy spectrum of 36 million tritium beta-decay electrons recorded in 259 measurement days excluded most of the parameter space suggested by previous claims for a sterile neutrino.

These experiments cost a total of (20+70)=90 million dollars. But their goal to explain past anomalies was not a waste. Testing potential explanation of anomalies, here in terms of a new ghost particle, is at the foundation of scientific frontiers that attempt to expand our scientific knowledge.

Yet, self-declared experts insist that anomalies of interstellar objects like 1I/`Oumuamua or 3I/ATLAS should only be framed in the context of our past knowledge on asteroids or comets. Any discussion that goes beyond these categories is “nonsense on stilts” as phrased here by the dogmatist Chris Lintott, only a few weeks after the interstellar object 3I/ATLAS was discovered and well before we had any detailed data about its properties.

By now, I had written 11 papers on 3I/ATLAS (available here). At the end of my first paper (posted here), I included the concluding sentence: “If 3I/ATLAS is a solid object with a physical radius larger than 10 kilometers, then the limited interstellar reservoir of rocky materials would suggest that its trajectory favored a plunging orbit towards the inner Solar system, perhaps by technological design”. As editor of the journal where my paper was submitted, Lintott insisted that I remove this sentence before the paper gets accepted for publication. His insistence motivated me to co-author a full paper on the technological interpretation (accessible here), which was peer-reviewed and accepted for publication in another journal.

No dogmatist commented on the anomalies leading to the notion of sterile neutrinos as “nonsense on stilts” even after the effort to validate this notion failed. Why is the idea of a technological origin for interstellar objects far more controversial than the failed idea of sterile neutrinos? In terms of risk management, the search for sterile neutrinos clearly does not hold more promise given the latest experimental data. Moreover, alien technology has more relevance to the future of humanity and hence deserves scientific attention.

This was the question I discussed with the president of the Templeton Foundation, Tim Dalrymple, and his daughter, during their visit to my home today, when we pondered over the latest frontiers of science.

A genuine curiosity about anomalies is common among science enthusiasts outside academia. Over the past day, I received the following two messages which shed more light on this state of affairs.

***

Letter 1:

“Dear Professor Avi Loeb,

I hope this email finds you well.

Please accept my deepest gratitude for the extraordinary work you continue to do. Through your bold ideas, rigorous scientific inquiry, and fearless exploration of the unknown, you have truly opened a new universe of learning — not only for the scientific community but for our entire planet and for generations yet to come. Your willingness to challenge conventional thinking and pursue evidence wherever it may lead has rekindled humanity’s sense of wonder about the cosmos and our place within it.

Like millions of others around the world, I am now following the trajectory of the interstellar visitor 3I/ATLAS with bated breath. The coming days, culminating in the critical observational window around December 19th, feel historic. We await with great anticipation whether this mysterious object will make a close approach to Earth — offering us an unprecedented opportunity to study an object from another star system up close — or whether it will continue its silent journey toward Jupiter and the outer solar system.

Whatever its path, the mere possibility of such an event reminds us how fragile, precious, and interconnected our perspective of the universe truly is. Your voice has been instrumental in helping us recognize these moments when they arrive.

Thank you once again for your inspiration, courage, and dedication to the pursuit of truth. With profound admiration and excitement for what the coming weeks may reveal.

3I/ATLAS

On the night of 19 December

we stand barefoot on terraces,
the city finally silent,
our palms open to the sky
as if a comet can be held
the way a child holds a firefly — 
not to trap it,
but to believe for a moment
you belong to hearts
a silver needle sewing inky velvet of space

with hope, we wonder if we will never part…


Warm regards,

Rina Tripathi”

Letter 2:

“Dear Avi,

I honorably think your colleagues fall into four categories, but not all are the same: (1) Jealousy; (2) Extreme jealousy with possible antisemitism operative; (3) A fundamental belief that there’s a close to zero percent chance that an artifact will ever or has ever come through the solar system; and (4) A basic misunderstanding of what you are doing.

Mostly you’re looking at the binary discourse comet/asteroid comet/asteroid and saying, “Gang, let’s always include a third category when objects arrive that behave in unfamiliar ways. If we don’t even imagine the possibility, then like 1I/’Oumuamua, we’ll force the comet/asteroid slipper to fit any foot.” Somehow, 1I/’Oumuamua has been rendered a comet in the history books. The truth is that you can offer a natural hypothesis for 1I/’Oumuamua, but the problem is self-evident. The crush of explanations to avoid the possibility of including an artificial object was so emphatic that, “Me thinks the… [self-declared experts] … doth protest too much.” What I think everyone misses, is that you’re not so interested in rocks and comets anymore. You’re interested in first seeing if an object might be something far more interesting. When I go to the beach, and poke around a tide pool, I know that there’s a lot of rocks and sand, but I’m looking for something more interesting.

A particle physicist is searching for a new particle. They search the debris from the supercollider for something other than up or down quarks. I don’t see the difference between that wholly accepted search and your search which is criticized. Particle physicists search the familiar data endlessly for an anomaly. Nobody expresses public animosity.

And Avi, the few substantial astrophysicists who feel the need to criticize your work reveal a blind spot and something misguided in their fundamental make-up. It’s an admission of conventionality. An interstellar meteor has properties that are curious. You mount an expedition to take a look. And because someone can find a road with trucks, that one data point dismisses your entire endeavor. It’s a search to discredit, not a search for truth.

Unless I missed something, we don’t know what 1I/’Oumuamua was, and my own sense is that even an interstellar comet might have been visited by another curious civilization so there could be probes on the surface from long ago. And my new thought is that if an interstellar comet is coming through the solar system, why not use that existing infrastructure to place a variety of sensory on it without having to launch the core infrastructure. Billions of years is a long time and it could be many things we don’t even consider even if it’s a comet also.

I am certain of one thing, you are the one scientist going to, “take a look”. Nobody else will find anything more than a marginal (2-sigma) possibility of life from dimethyl sulfide in an exoplanet atmosphere or phosphine in Venus’ atmosphere. I’d be excited to find a prokaryote somewhere, but why are we setting our sights so low?

Josh Ravetch

Playwright, Los Angeles”

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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