The interstellar visitor, known as 3I/ATLAS, is perplexing astronomers. Unlike normal comets, which develop a trail of dust and gas as they heat up during a pass near the Sun, this comet hasn’t displayed such a tail in recent observations. This bizarre behaviour has confounded researchers and given rise to speculation about what the comet really is and where it came from.
Discovery and Initial Observations
3I/ATLAS was discovered near our Solar System in June 2025 by the NASA-sponsored ATLAS telescope, also located in Chile. As the third interstellar object detected passing through, it immediately became a focus of attention. Its highly eccentric orbit verified that it came from outside our Solar System, and early observations even showed a coma—a hazy envelope of gas and dust—surrounding its icy core, which was believed to be no more than 5.6 km across.
Astronomers thought that when 3I/ATLAS got closest to the Sun (perihelion), the heat would make it lose materials, which would make the bright tail that is typical of comets. Recent pictures taken on November 5, 2025, from the R. Naves Observatory in Spain, on the other hand, showed no tail at all.
The Missing Tail Mystery
Certainly, the absence of a tail challenges long-held beliefs about comet behaviour. Typically, solar radiation pressure and solar wind blow away gas and dust from the comet’s centre, creating a tail that points away from the Sun. The images of 3I/ATLAS revealed a small, compact spot of light with no trailing rubble or gas clouds.
Avi Loeb, an astrophysicist at Harvard, and other scientists have stated that, based on standard comet models, approximately 13% of the object’s mass should have clearly dispersed into a tail by now. Instead, it is still a whole, small object with no clear signs of losing mass.
One potential reason the comet’s tail is hidden from our view could be that it lines up perfectly behind the comet when viewed from Earth, compared to its angle in relation to the Sun. Therefore, it may not be visible to telescopes on Earth due to perspective effects. However, it is presently difficult to confirm this hypothesis before the other perspective changes.
The Green Glow and Unusual Composition
One possible explanation why we aren’t seeing the comet’s tail might be that its relative location due to the viewing point (Earth) is in a position where it lines up perfectly behind the comet, but not necessarily when regarded from another angle with respect to the Sun, and so isn’t visible with any telescope on Earth because of perspectival considerations. However, it is not easy to validate this point of view at the moment, as another one may shift.
Studies show that the comet contains a significant amount of carbon dioxide, with levels that are 16 times higher than those of most other comets in the Solar System. The high level of CO2 in 3I/ATLAS suggests that it formed in a very cold, faraway place, far from its original star.
Scientists believe that billions of years of exposure to cosmic rays may have significantly altered the comet’s surface, which would have impacted its chemical and physical behaviour. Experiments in the lab that mimic cosmic ray bombardment on comet-like ices show similar levels of CO2 and dark, carbon-rich residues, which support this idea.
Speculations on the Nature of 3I/ATLAS
Some scientists have wondered whether 3I/ATLAS is a natural comet or an artificial object, such as an alien probe, because it exhibits peculiar motion and lacks a tail. These ideas are controversial and speculative, but the comet’s unusual properties continue to spark discussion and draw people’s attention.
There is a consensus that 3I/ATLAS remains a mystery and may prompt astronomers to reevaluate their understanding of how interstellar objects form and survive in space.
What Lies Ahead?
As 3I/ATLAS recedes from the Sun and attitudes shift, observations will presumably become more detailed. Future data may confirm whether the tail is indeed absent or obscured. The object is still being studied through spectral and imaging observations to determine its composition and behaviour, which would inform our knowledge base of interstellar visitors in general and cosmic phenomena at large.