14th anomaly detected in 3I/ATLAS: Rotation axis points toward Sun
A recent article published on Medium by Avi Loeb, head of the Galileo Project and founding director of Harvard University’s Black Hole Initiative, highlights the discovery of a new anomaly in the interstellar object 3I/ATLAS, highlighting a rare alignment of its rotation axis with the Sun.
The study, which observed a periodic wobble in the anti-tail jet of 3I/ATLAS during July and August 2025, indicates that the jet base is offset by less than 8 degrees from the poles of the nucleus’s rotation axis. As the nucleus spins, the jet precesses along a cone surrounding this axis, News.Az reports.
This alignment suggests that, at large distances from the Sun, 3I/ATLAS maintains a steady dayside and nightside, which switch roles at perihelion due to the rotation axis being nearly sunward. If the jet originates from a natural pocket of ice that sublimates under sunlight, this configuration represents a 14th anomaly for 3I/ATLAS, adding to the 13 previously identified anomalies.
The anomaly is significant because the probability of the rotation axis aligning within 8 degrees of the Sun at a heliocentric distance greater than five astronomical units is only 0.5%. Without this alignment, the anti-tail jet would have deviated more sharply from the rotation axis, showing a larger wobble in position angle and potentially exhibiting prominent gaps in activity as its base moved between the dayside and nightside of 3I/ATLAS.
This coincidence applies to the geometry of the anti-tail and the rotation axis of 3I/ATLAS before perihelion. However, the remarkable new revelation after its perihelion on October 29, 2025,gleaned from the latest images taken by the Hubble Space Telescope and ground-based telescopes, is that 3I/ATLAS still shows a prominent anti-tail jet in the direction of the Sun. This is despite the fact that 3I/ATLAS is currently receding away from the Sun and its Sun-facing side used to be on its night-side when 3I/ATLAS was approaching the Sun in July-August 2025.
Images of the interstellar object 3I/ATLAS. Thin purple lines indicate the position angle of the detected anti-tail jet at a projected distance of 6,000 kilometers from the brightness peak (dotted red circle). For each frame, the observation date and the start and end times in UTC are shown above the panels, along with the total number of sidereal-tracking exposures and the cumulative integration time. The projected velocity vector (red arrow) and the anti-solar direction (yellow arrow) are marked, as well as the image scale and orientation. Degraded orange lines denote the projected rotation-axis direction, derived from mean value of the anti-tail positions angles, while yellow lines trace the tail direction. Brightness contours are overplotted using ten logarithmically spaced levels between the 20th and 95th percentiles of pixel intensity in each frame. The anti-tail refers to the narrow, linear, black feature extending roughly northwest in the direction of the Sun. (Image credit: Serra-Ricart, Licandro & Alarcon 2025)
The base that launched the anti-tail jet in July 2025 is now on the night-side of 3I/ATLAS. The comet interpretation of 3I/ATLAS requires a new pocket of ice near the opposite pole of the rotation axis, that gives rise to a prominent new anti-tail jet after perihelion. In addition, it requires insolation of the previously active jet before perihelion, so as for it to become dormant after perihelion — constituting yet another anomalous feature.
Since the new anti-tail is observed to be collimated to within 8 degrees out to half a million kilometers in the latest image of 3I/ATLAS — taken on December 15, 2025, the proximity of the new jet base relative to the rotation axis and the Sun’s new direction raises the 14th anomaly to the second power. In other words, the chance of two major pockets of ice being located near the rotation poles of 3I/ATLAS, so that one of them would be on the dayside when 3I/ATLAS approaches the Sun from a great distance and the other is on the dayside when 3I/ATLAS is on its way out of the Solar system, while both being within 8 degrees of the nearest rotation pole when facing the Sun, is the square of 0.005 or a tiny probability of merely 0.000025.
Of course, a technological spacecraft might have a reason for aligning the outflow of gas from its thrusters in the direction of the Sun. We do not have high-resolution images of the jet direction near perihelion.
The tight collimation of the anti-tail out to a distance of half a million kilometers, larger than the distance to the Moon, despite the solar radiation pressure and wind after perihelion, raises new questions. Why does the sunward jet maintain its collimation without being broadened or pushed away from the Sun? What is its speed and mass loss rate? Hopefully, upcoming spectroscopic observations of the material it carries will clarify the launch mechanism of the anti-tail.
The derived periodicity of 7.74 (± 0.35) hours in July-August 2025, could imply a nucleus rotation period of 15.48 (± 0.70) hours if the anti-tail originates from a single active spot at any given time. This value is indeed consistent with the rotation period derived during July 2025 from the periodic brightness variability of 3I/ATLAS: 16.16 (± 0.01) hours.
For a nucleus radius of 2 kilometers with a rotation period of 15.5 hours, the centrifugal acceleration of the surface of 3I/ATLAS is 0.0025 centimeters per second squared. This value is tiny, just 2.6 millionths of the gravitational acceleration on the surface of Earth, 1-gee. The rotation period needs to be shortened to 1.5 minutes in order to create an artificial gravity similar to 1-gee.
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