An unprecedented sun-directed structure on interstellar object 3I/ATLAS has exhibited an unexpected wobble near the Sun, prompting intense scientific debate.
Harvard University astrophysicist Professor Avi Loeb has called for a rigorous investigation into this behaviour. Loeb states that the object's 'anti-tail' and its subsequent change in orientation cannot be fully explained by conventional cometary physics alone.
Anatomy of an Anomaly
Astronomers have been observing the interstellar visitor since its discovery on 1 July 2025. They anticipated normal cometary behaviour as it neared perihelion on 29 October 2025. Instead, they witnessed a rare 'anti-tail' pointing toward the Sun. That structure recently displayed a change in orientation, or wobble.
Anti-tails are a seldom-observed feature. They are typically an optical illusion caused by Earth's viewing angle, where large dust grains appear to point toward the Sun. 3I/ATLAS defies this explanation. Detailed analyses show the structure was a physical presence, visible both before and after its perihelion.
In a series of technical papers, Loeb and colleague Eric Keto proposed the anti-tail could arise from physical processes within the comet's coma. Their models describe how large ice grains, formed by the sublimation of volatiles like carbon dioxide (CO₂), could scatter sunlight toward the sun.
Some astronomers accept this explanation. Others emphasise that such a pronounced and persistent anti-tail is rare. The prevailing view among traditional comet specialists is that these features can arise naturally. Loeb disagrees. He argues the anti-tail's persistence and its wobble suggest a complexity beyond common models. According to Loeb's posts on Medium, the structure was a genuine physical jet. Its unusual behaviour could signal gaps in current understanding.
The wobble, if confirmed, could indicate a variation in the jet's emission or its interaction with solar radiation, raising unresolved questions about the forces shaping the comet's structure.
A Debate Over Interstellar Visitors
The scientific debate centres on whether established comet physics can reconcile all observed phenomena. 3I/ATLAS is only the third confirmed interstellar visitor. The first was 1I/'Oumuamua in 2017. The second was 2I/Borisov in 2019. Each object presented unique characteristics. 2I/Borisov behaved like a typical solar system comet. 'Oumuamua did not. Its elongated shape and non-gravitational acceleration—pushing away from the Sun faster than gravity alone could explain—led to intense speculation.
Professor Loeb famously co-authored a paper suggesting 'Oumuamua could be an object of artificial origin. This controversial stance has positioned him as a figure willing to consider exotic explanations for astronomical anomalies. That reputation informs the current debate over 3I/ATLAS.
Supporters of the conventional viewpoint point to astrophysical studies showing how large dust grains might remain sunward long enough to create an anti-tail. They explain that the structure's evolution from an anti-tail to a traditional antisolar tail near perihelion matches known thermodynamic effects. Critics of Loeb's interpretation note that astronomers have documented anti-tails in other comets.
Loeb highlights additional anomalies in 3I/ATLAS, including its large inferred mass. He argues these features compound the mystery. The astrophysicist has emphasised the need for the scientific community to keep an open mind.
🚨 Interstellar Object 3I/ATLAS Behaves Unlike Normal Comets
— Astronomy Vibes (@AstronomyVibes) December 16, 2025
Harvard astrophysicist Avi Loeb says 3I/ATLAS is displaying an unusual sun-facing anti-tail that may not be explained by a simple viewing-angle effect, unlike what is seen in ordinary comets.
Recent observations… pic.twitter.com/AEgMbINSMR
A Closing Window for Observation
3I/ATLAS will make its closest approach to Earth on 19 December 2025. Astronomers are preparing a coordinated suite of observations. Ground-based telescopes, space observatories, and ESA's JUICE spacecraft are poised to capture further data on the object's activity, composition, and tail morphology.
High-precision measurements over the coming weeks are essential. They will resolve the nature of the anti-tail's wobble and test competing hypotheses. If the behaviour can be mapped against predictive models, scientists may determine whether the structure arises purely from sublimation and radiation or if alternative mechanisms are at play. One of the most enigmatic visitors ever observed continues its passage through the solar system, challenging long-held assumptions about cometary science.
