The newly discovered object 3I/ATLAS (officially designated C/2025 N1) has taken the astronomical community by surprise. Detected in early July 2025 by the ATLAS survey in Chile, it quickly became clear that this wasn't an ordinary comet. Its hyperbolic orbit, meaning it is not gravitationally bound to the Sun, confirmed that 3I/ATLAS came from beyond our Solar System. It is only the third interstellar object ever observed, following 2017's ʻOumuamua and 2019's 2I/Borisov.
The discovery triggered an immediate international response. Astronomers from NASA, ESA, and observatories across the globe scrambled to point their instruments at the object, eager to capture data before it drifted too far into the darkness. Within days, observations confirmed that it had a visible coma, the hazy envelope of gas and dust that gives comets their distinctive appearance. Unlike ʻOumuamua, which remained oddly asteroid-like and without a tail, 3I/ATLAS is visibly active -- a clear sign of volatile material evaporating as it approaches the Sun.
Early estimates suggest the nucleus measures only a few kilometres across, but the dust and gas trail it leaves behind stretches tens of thousands of kilometres. Its closest approach to the Sun (perihelion) will keep it at a safe distance, oughly 1.4 astronomical units away, ensuring it poses no threat to Earth. Still, the scientific importance of the find cannot be overstated. Each interstellar visitor provides a snapshot of material that formed around another star, offering rare insight into how other planetary systems are built.
What has truly captured scientists' attention is the comet's chemical composition. Spectral data from the James Webb Space Telescope and other instruments have revealed an unusually high ratio of carbon dioxide (CO₂) to water (H₂O) in its coma. In simple terms, this comet contains far more carbon dioxide than the ones we're used to seeing closer to home.
This discovery raises several fascinating possibilities. The high CO₂ levels might suggest that 3I/ATLAS formed in an extremely cold part of its home system, where carbon dioxide could freeze easily while water remained locked away. Alternatively, its long interstellar journey may have altered its outer layers, allowing CO₂ to sublimate more readily when it entered our Sun's warmth. Astronomers have also noticed that its jets, streams of gas erupting from the nucleus, behave in an asymmetric way, with one side of the comet showing much more activity than the other. This could mean that the surface is patchy, with different areas heating unevenly. For researchers, this is a clue to the comet's internal structure and its journey through the interstellar medium.
In the media, some have sensationalised these unusual readings, referring to them as a mysterious "signal" or even suggesting that NASA had issued a "cosmic alert." In reality, there is no evidence of anything artificial or alarming. The "signal" is a scientific term referring to the spectral data, the light signature that helps astronomers identify the materials making up the comet. The only "alert" NASA issued was to encourage global observatories to collect as much data as possible before the comet fades from view.
These key details show why 3I/ATLAS has become such a focus of scientific excitement. Its chemistry and activity levels differ significantly from those of comets that formed in our Solar System, suggesting that planetary systems across the galaxy may vary far more than once thought.
For the public, it's a reminder that "interstellar" doesn't mean "dangerous." The comet's arrival offers a rare scientific opportunity, a glimpse into the material that formed around another star, travelling for millions of years before briefly visiting our cosmic neighbourhood.
While the comet will not be visible to the naked eye, it is accessible with moderate telescopes and astrophotography setups. Observers are advised to:
This careful observation allows scientists and hobbyists alike to document the comet's changing behaviour, contributing valuable data to ongoing studies.
Scientists hope 3I/ATLAS will reveal how common interstellar objects really are. Until a few years ago, none had ever been seen; now, three have been detected in under a decade. This hints that fragments from other planetary systems are passing through our cosmic backyard more often than anyone realised.
Each interstellar visitor tells a slightly different story. ʻOumuamua was oddly cigar-shaped and may have been a fragment of a larger body. Borisov looked more like a typical comet, and now 3I/ATLAS offers yet another twist, one rich in carbon dioxide and marked by strange outgassing behaviour. Together, these findings could reshape our understanding of how planets and comets form around other stars.