New Analysis of the Periodic Wobbles of the 3 Jets Around 3I/ATLAS

A symmetric structure of three equally-separated jets is apparent near the nucleus of 3I/ATLAS, after applying the Larson-Sekanina rotational gradient filter to two exposures by the Hubble Space Telescope on 2025–12–27 UT. Two of the jets, separated by about 120 degrees, are prominent in both images, but their structure broadens into a wider fan on the right panel. Such morphological changes modulate the amplitude of the brightness variability. (Image Credit: T. Scarmato and A. Loeb 2026)

In a new paper (accessible here) that I co-authored with the Italian observer Toni Scarmato, we use images from the Hubble Space Telescope to study the motion of the symmetric system of three jets around the nucleus of the interstellar object 3I/ATLAS.

The Hubble images were processed through a Larson–Sekanina rotational-gradient filter -which removed the circularly symmetric glow around the nucleus. The remaining brightness map shows three close-in jets in addition to a sunward anti-tail on a much larger scale, as discussed in our previous paper here.

These post-perihelion Hubble Images were taken between November 30 and December 27, 2025. The most prominent jet among the three is directed opposite to the Sun and appears to wobble over a period of 7.20 (± 0.05) hours. The total brightness shows contemporaneous variability with a period of 7.136 (±0.001) hours and an amplitude of about 30%. We interpret the characteristic post-perihelion period of about 7.1 hours as an attitude precession or nutation associated with a misalignment of the rotation axis with the symmetry axes of the nucleus. The wobble around the rotation axis displays a characteristic angular excursion of order 20 degrees, while the rotation axis is aligned with the sunward direction to within 20 degrees.

The bottom panel shows the schematic geometry of the 3-jet system near the nucleus of 3I/ATLAS (excluding the prominent anti-tail outflow towards the Sun), based on the filtered Hubble brightness map in the top panel. The projected spin axis in the sunward direction appears at a position angle of PA= 110 degrees, and the anti-sunward direction is at PA= 290 degrees. The PAs and oscillation half- amplitudes of the 3 jets are as follows: Jet 1: 55 (± 12.8) degrees; Jet 2 (sunward): 290 (± 20) degrees; Jet 3: 170 (± 12.6) degrees. The anti-sunward jet at PA=290 degrees wobbles with period of 7.2 hours. (Image Credit: T. Scarmato and A. Loeb 2026)

Based on the inferred diameter of 2.6 kilometers for the nucleus of 3I/ATLAS (as reported here), only about a percent of the brightness of 3I/ATLAS originates from the reflection of sunlight by its nucleus. When rotation is misaligned with the symmetry axes of the nucleus, it can produce quasi-periodic wobbles and a non-sinusoidal variability. The new analysis links the inferred 7.1-hour period to an attitude precession or nutation of the multi-jet system. The brightness variability tracks transitions between collimated and fan-like morphologies of the jets.

The phase-folded light curve of 3I/ATLAS shows a period of about 7.14 hours. (Image Credit: T. Scarmato and A. Loeb 2026)

Whereas the position angle of the most prominent jet shows variability with a period of 7.20 (± 0.05) hours, shorter periods are also apparent. Jet 2 shows a period of 2.9 hours and Jet 3 shows a period of 4.3 hours. The sum of 2.9 plus 4.3 is 7.2 hours.

The phase-folded variability of the position angle of Jet 2 shows a period of about 2.9 hours. (Image Credit: T. Scarmato and A. Loeb 2026)

The phase-folded variability of the position angle of Jet 3 shows a period of 4.3 hours. (Image Credit: T. Scarmato and A. Loeb 2026)

Summary of the inferred periods in the wobble of the jet system around 3I/ATLAS. (Image Credit: T. Scarmato and A. Loeb 2026)

We interpret the ~7.1-hour periodicity as the result of the rotation of 3I/ATLAS being misaligned with the principal symmetry axes of its nucleus. The jet structure undergoes a quasi-periodic wobble as the nucleus exhibits precession and nutation about the rotation axis. This interpretation explains the orientation oscillations of the jets with morphology-dependent amplitudes and phases, the non-sinusoidal variability, and the sensitivity of the lightcurve to evolving collimation (fan opening) of the jets.

Multiple jets in different directions tend to balance each other and stabilize the rotation of 3I/ATLAS. Jet 2 — which is oriented approximately opposite to the Sun and close to the projected rotation axis — anchors the large-scale geometry, whereas Jets 1 and 3 trace the precession cone through their position angle oscillations. The wobble and changing collimation of the jets modulates both the projected jet directions and the total brightness.

The fundamental question that remains unresolved is whether the symmetric triple-jet system is a signature of technological thrusters or the sublimation of natural pockets of ice on the surface of a natural rocky iceberg.

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.

Professional website:

https://lweb.cfa.harvard.edu/~loeb/

Social media:

https://avi-loeb.medium.com/
https://www.youtube.com/@ProfessorAviLoeb

https://open.spotify.com/show/1zhndXkvSY2b8FdjspFpCd
https://x.com/ProfAviLoeb