Why is the Anti-Tail Sunward-Jet of 3I/ATLAS Tightly Collimated?
My latest essay on the 14th anomaly of the interstellar object 3I/ATLAS (available here) focused on the alignment of its rotation axis with the sunward direction at large distances. The fact that a tightly collimated jet appears as the anti-tail in the direction of the Sun both before and after perihelion has a tiny probability of occurring at random, 0.000025.
But the collimation of the jet to within 8 degrees out to a distance of half a million kilometers, as seen in the latest images of 3I/ATLAS from December 15, 2025 (and discussed here), is also a highly unlikely occurrence.
My brilliant colleagues, Dr. Eric Keto and Dr. Frank Laukien, independently offered their important insights on this matter.
Eric wrote:
“The pre-perihelion anti-tail is a sunward jet located near the rotation axis that happens to align with the sunward vector. This makes it spin like a rifle bullet around its direction of travel which was sunward. There is no necessary connection between the jets on either side of perihelion.”
The paper that Eric and I co-authored about the Hubble Space Telescope image from July 21, 2025 (available here), concluded that the anti-tail before perihelion must be a tightly collimated jet that is about ten times longer than it is wide. This is because its long axis extends in the Hubble image towards the Sun twice as far as its width, but the jet is viewed from an angle of 10 degrees relative to its long axis — which adds an extra projection factor of [1/sin(10)]=5.8, making the actual length-to-width ratio about 11.6. Indeed, the latest images of 3I/ATLAS from this week show a sunward jet that is about ten times longer than it is wide, with an opening angle of order 6–8 degrees.
What natural mechanism could explain a tightly-collimated anti-tail jet both before and after perihelion in the direction of the Sun?
The rotation axis of 3I/ATLAS in July-August 2025 was aligned to within 8 degrees with the sunward direction according to a new report here. This implies that the base of the new anti-tail jet after perihelion must have been on the nightside of 3I/ATLAS before perihelion and the base of the old anti-tail jet must be on the nightside of 3I/ATLAS after perihelion. For them to be active only when facing the Sun, they must be well insulated on the nightside, a non-trivial 15th anomaly for a natural comet.
Why would these independent bases near the opposite poles of the rotation axis both produce tight jets with an opening angle of order 6–8 degrees?
Frank wrote:
“Avi,
Only a typical natural cometary tail (not anti-tail) could be tightly collimated by sunlight, since the Sun is essentially a point source from the point-of-view of the comet, and gas or dust that gets sublimated by sunlight into a full hemisphere of 2pi solid angle, then quickly gets pushed away in a tightly collimated comet tail by the solar wind and light.
On the other hand, I cannot see how a tightly collimated natural anti-tail could get created: any large or object-covering ice field would generate a forward plume that would fill a 2pi solid angle, assuming an approximately spherical object and sublimation primarily in a direction that is orthogonal to the surface, and not primarily colinear with the incident sunlight.
Hypothetically, a very deep ice pocket, shaped like a gun barrel, may emit a tightly collimated natural gas and dust beam, but the sunlight would only shine down that ‘gun barrel’ of a rotating object for a brief moment.
If the collimated, modulated anti-tails pointing towards the Sun are technological, they could be:
· for propulsion (doesn’t make sense), unless propulsion away from the Sun had some intentional navigational effects to achieve or avoid ‘something’, or
· as directed weapons (doesn’t make sense after perihelion, as they no longer ‘clear the way’ of the object of debris), or
· to create a directed shield against sunlight and solar wind to protect the technological object’s electronics or biological content or surface?
Best wishes,
Frank”
As it turns out, I was just contemplating the last possibility in the context of a technological thruster before Frank’s message arrived. His insights are important.
Observing 3I/ATLAS on a retrograde trajectory which is aligned to within 5 degrees with the ecliptic plane of the planets around the Sun was the initial trigger to consider a technological origin for it. The near alignment of its rotation axis with the direction of the Sun at large distances is another reason to consider this possibility. Finally, the appearance of tightly collimated anti-tails before and after perihelion add to the mystery.
These are all rare geometric coincidences that cannot be easily brushed aside by NASA’s narrative at the press conference here that: “3I/ATLAS is definitely a comet with qualities that can be naturally explained by its different birth environment.” How can a different birth environment explain these geometric anomalies which are unique in reference to the Solar system orientation?
NASA’s suggestion that “rare things happen” must attend to the fact that the probability for the 5-degrees trajectory-alignment with the ecliptic plane (0.002) times the probability for the 8-degrees rotation-axis alignment with the direction of the Sun at large distances (0.005) times the probability of two independent bases that produce tightly-collimated jets to within 8-degrees from the rotation poles (0.000025), gives a net probability of one part in 4 billion!
This resulting probability of 0.00000000025 does not factor in other anomalies (as listed here), like the detection of much more nickel than iron as found in industrially-produced nickel alloys. This raises two questions:
1. What is 3I/ATLAS?
2. Why are self-declared “comet experts” not curious about the first question.
ABOUT THE AUTHOR
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.
