In the infinite horizon of the cosmos, comets seem to follow a simple rule: when they approach the Sun, their ice sublimates (they go from solid to gas, without going through the liquid stage), releasing gas and dust, and forming a tail that extends in the opposite direction to the Sun, pushed by the solar wind and radiation. But our most famous interstellar visitor, 3I/ATLAS breaks that seemingly unbreakable rule in a way never seen before.
According to an image captured on August 2, 2025 by the Teide Observatory TTT (Two-meter Twin Telescope) telescope array, 3I/ATLAS shows an “anti-tail”: the gases released when approaching the Sun are directed towards it, not in the opposite direction. And that had never been seen before.
Composed of 159 exposures of 50 seconds each, the image shows a fine “jet” or current that is projected towards the Sun, identified by a purple line in the study illustration that extends about 6,000 km from the object’s core.
This anomaly raises two new questions that, in Loeb’s words, “They can change our understanding of what a comet is… or what 3I/ATLAS is”since the usual explanations do not work well in this case. In fact, the first thing they have confirmed is that it is not an effect caused by perspective (when the line of sight of the Earth and the orbital geometry make it appear that a tail is pointing towards the Sun) or distance, but that, in fact, the tail is directed towards it.
The study’s proposal is an answer based on the laws of physics. According to their calculations, when an object as fast and massive as 3I/ATLAS approaches the Sun, it does not heat up uniformly. Instead of melting equally over its entire surface, solar heat generates a kind of “uneven melting zone.”similar to a strip of snow that melts sooner on one sunny slope than on another. That stripe, called anisotropic snow line in technical terms, could cause the largest and heaviest particles to be released just on the side facing the Sun, rather than the opposite side, as occurs in common comets.
The visible result would be a stream of material pointing directly toward the Sun, a true anti-cola natural and, until now, unique in the observed universe. However, this explanation is still not entirely convincing, and many experts remain cautious. The idea that there is an unknown mechanism or a behavior that has never been documented opens the door to more radical hypotheses.: This object might not behave like the solar system comets we know.
And this is important not only for the case of this object. If 3I/ATLAS is a “normal” comet, we are seeing a new phenomenon that will require revising models of cometary activity. And, if it is not a “normal” comet, we could be looking at something different: an interstellar object that operates with different rules. And that has enormous implications for astronomy, the formation of solar systems and the search for interstellar objects.