Could the tail of a comet possibly point towards the Sun and possibly signify something extraordinary? This is the question that is fascinating scientists as the interstellar comet 3i/ATLAS continues to pass through the solar system, complete with an inexplicable “anti-tail.”
Since its detection inJuly of 2025 by the NASA ATLAS survey telescope situated in Chile, the object designated 3I/ATLAS has remained observable by a host of earth- and space-based telescopes such as the Hubble Space Telescope and the newly launched Webb Space Telescope. A typical comet will transmit one or more tails away from the Sun as its molecules are affected by solar pressure and the solar wind. Interestingly, high-resolution photographs of the object on the 21st ofJuly and the 13th of December by the Teerasak Thaluang telescope located in Thailand depict an object that trails an extended structure aimed at the Sun.
Harvard astrophysicist Avi Loeb dubs it a “real physical jet” and contends that it is not just an optical perspective. This premise stems from the fact that there are thousands of images which have persisted in the same orientation even after the comet’s perihelion passage in late October. Loeb associates the phenomenon with “non-gravitational acceleration” the subtle increase in speed that cannot be attributed to the Sun’s gravitational pull and speculates that the phenomenon might have been the result of propulsion engineering. As Loeb says: “a swarm of objects lagging behind an artificial craft or even a mothership designed to release small probes.’”
There is a mainstream explanation for comets based on the physics of heat and the dynamics of particles. The day side of the comet is strongly heated by the sun, and the larger dust particles and ice grains are scattered towards the sun. The particles, some of which are bigger than 100 microns, are too heavy to be effectively propelled by the radiation pressure and take a while to be deflected into the antisolar tail. UCLA’s David Jewitt explains: “All these things are consistent with a comet nucleus of typical size or smaller, sublimating in sunlight and blowing out dust particles. Nothing really shocking there.”
The anti-tail extent in Hubble’s July observations, with a Haser-type density model, is found to be longer in the sunward direction, at 29,600 km, than perpendicular directions, as required by a physical model that correlates the life-length of ice grains with their terminal velocity and sublimation time, with greater life-length of ice grains with lower velocities and longer lifetimes in the sunward direction, producing the anti-tail. The physical model also reveals that ice grains are dominated by volatile ice, which corresponds to an exponential scattering decrease.
The composition is also important. The nucleus may consist of 80% H₂O ice and 20% CO₂ ice, according to analysis. CO₂ ice sublimates readily at lower temperatures, cooling the surface. Water ice sublimation is also inhibited, though ice grains may undergo sublimation after gas drag if they enter the coma. The variability of the snow-line radius, a factor of seven, is a function of hour angle, ∼ ± 90°, and is consistent with illumination angle asymmetry.
Such detail requires sophisticated imaging methods. Observers use techniques such as the Larson-Sekanina rotational gradient filter to improve jet signatures, although, as a broad anisotropy, it is only apparent on a scale of some 60 pixels, as predicted by sublimation-induced disruption as opposed to jets. The simulation run by NASA’s Eyes on the Solar System depicts its hyperbolic orbit, indicating that it is an unbound comet to our Sun, which will pass out of the solar system upon its close Earth Approach of 170 million miles on December 19.
Non-gravity accelerations in comets are estimated with multiple orbits, whereas for interstellar travel objects such as 3I/ATLAS, only a single orbit is possible, with acceleration sensitivity of a few hundred millionths of Earth gravity achieved via new methods involving interplanetary spacecraft flybys. In the case of 3I/ATLAS, the acceleration of its speed increased from 137,000 mph at discovery to 153,000 mph due to gas forces near perihelion passage.
For amateur astronomers in the Northern Hemisphere, the comet can be seen at a magnitude of 11 in other words, an eight-inch telescope is required to observe the comet at this time. At closest approach, the comet can be found in the area of star system Regulus in the constellation of Leo in the pre-dawn sky.
More than one tail or the anti-tail can be seen with long exposure photography. Regardless of whether the anti-tail is a manifestation of the thermal physics effect or alien engineering, the fact is that interstellar comets prove challenging not only to the observation abilities but also to the models of theoretical physics. As quoted byLoeb, “By recognizing anomalies, we can learn something new. By ignoring them, we remain ignorant.”
