Avi Loeb highlights tightly collimated anti-tail jet of interstellar object 3I/ATLAS

Harvard physicist Avi Loeb has published a new essay on Medium on December 17, 2025, drawing attention to another anomalous feature of the interstellar object 3I/ATLAS, as seen in the latest images obtained on December 15. 

Loeb pointed out that 3I/ATLAS has a “tightly collimated” jet as its sun-facing anti-tail, meaning that it appears as a thin, straight, well-directed stream which does not blur or fan out. 

He believes that for a natural comet to showcase this feature of a tight anti-tail jet before and after perihelion is extremely rare and unusual. 

To be precise, Loeb stated that the odds of such a strange occurrence happening at random are 0.000025. 

Noting how the stream of the jet remains well-focused rather than fanning out despite traveling an enormous distance, Loeb contemplates the possibility that 3I/ATLAS has a technological origin. 

While he remains open-minded about the anomalies of the interstellar object, he called out the “experts” for not paying any heed to the unusual properties of the visitor as it prepares to make its closest approach on December 19, 2025. 

More details on Harvard physicist Avi Loeb’s deep dive into the geometry of the collimated anti-tail jet of 3I/ATLAS

After pointing out the unusual behavior of the sunward anti-tail of the interstellar object, Loeb shared the inputs of two of his colleagues – Dr. Eric Keto and Dr. Frank Laukien – on the latest observation.

According to Dr. Keto, the jet seen before perihelion and the one seen after that appear to have emerged from different sources, as he wrote that there is “no necessary connection” between them. 

“The pre-perihelion anti-tail is a sunward jet located near the rotation axis that happens to align with the sunward vector. This makes its spin lie a rifle bullet around its direction of travel, which was sunward,” he explained.

With that explanation, Loeb added that when he and Dr. Keto wrote a paper on the July 21, 2025, image of the interstellar object, they deduced that the “anti-tail before perihelion must be a tightly colimated jet,” which should be longer than wide. 

The latest images substantiated their observations were correct, but raised another important question. 

“What natural mechanism could explain a tightly-collimated anti-tail jet both before and after perihelion in the direction of the sun?” Loeb asked. 

Loeb’s other colleague, Dr. Laukien, added his thoughts, saying that “only a typical natural cometary tail” can show such a well-focused jet by sunlight, clarifying that such behavior was rare in anti-tails.

He explained that cometary tails facing the sun get heated and sublimate gas and dust in all directions.

Then, the solar wind and sunlight push the substances away, creating a well-focused tail pointing away from the sun. 

However, he noted that it was difficult to explain why a sunward anti-tail is displaying similar qualities. 

According to him, a “very deep ice pocket” may have caused such an unusual event to occur, but even so, since the object is spinning, the sun would only have shone on it for a brief moment.

As a result, the narrow jet would not stay for long. 

That said, Dr. Laukien noted that if 3I/ATLAS is technological, the anomaly of the jets can hint at a few things. 

It can be engines, which do not seem logical if the object intends to move forward, or “directed weapons,” which, Dr. Laukien believes, are useless since the object has nothing to clear in its path. 

A third possibility that he noted was the creation of a “shield” to protect itself from the solar winds. 

Keeping the points in mind, Loeb wrote that the collimated anti-tail jet only added to the mystery of the interstellar object. 

He then called out NASA for declaring 3I/ATLAS a comet, asking if there is an explanation for the geometric anomalies. 

Loeb further mentioned that the recent anomalies, including the alignment of the jet with the spin axis and the collimated jet, present “a net probability of one part in 4 billion!”

He concluded his essay, asking two prominent questions. First, “What is 3I/ATLAS?” and second, why are the “comet experts” not more invested in finding out that the interstellar visitor is? 

Stay tuned for more updates.