When astronomers first spotted a faint, fast-moving object racing through the outer Solar System in mid-2025, few expected it to challenge what we know about cosmic history. Now known as 3I/ATLAS, the object has become one of the most intriguing astronomical discoveries of the decade. Early observations suggest it did not form alongside our Sun, or even within our galaxy’s familiar stellar neighbourhood. Instead, researchers believe it may be a relic from the Milky Way’s earliest era, possibly billions of years older than Earth and even predating the Sun. As scientists race to study it before it vanishes back into interstellar space, 3I/ATLAS is offering a rare chance to study material forged around ancient stars, and, for some, it has even revived controversial questions about extraterrestrial technology.
How 3I/ATLAS was discovered and why it stands out
3I/ATLAS was detected on 1 July 2025 by the Asteroid Terrestrial-impact Last Alert System (ATLAS) observatory in Chile. Almost immediately, its trajectory raised eyebrows. Unlike ordinary comets bound to the Sun’s gravity, this object was moving far too fast to belong to the Solar System. Calculations confirmed it was on a hyperbolic path, meaning it had arrived from interstellar space and would eventually leave again.This made it only the third confirmed interstellar visitor ever observed, following 1I/‘Oumuamua in 2017 and 2I/Borisov in 2019. Officially designated C/2025 N1 (ATLAS), it quickly became known informally as 3I/ATLAS, reflecting its place in this rare class of objects.
3I/ATLAS stuns astronomers with its ancient age and unique chemistry
As also found that the one thing that truly puts 3I/ATLAS in a category of its own is its age. Research carried out by Associate Professor Michele Bannister of the University of Canterbury has revealed that the comet is anywhere between 8 and 14 billion years old. To put this in some kind of perspective, the Solar System is no older than 4.6 billion years. The comet’s incredible speed of 58 kilometres per second compared to the Sun’s pulling on it has a lot to do with this age classification. An object of this velocity would have originated in the Milky Way’s thick disk region, which houses some of the oldest stars in the entire Milky Way. If proven true, this means that 3I/ATLAS formed around a star that has very possibly died out well before the Sun existed.Spectroscopic observations yielded the fact that 3I/ATLAS has a chemical composition unlike Solar System comets. When 3I/ATLAS approached the Sun, strong spectral lines of atomic iron and extremely rare atomic nickel appeared in its spectrum. The James Webb Space Telescope also threw further light on the object. The comet seems to have a remarkable amount of carbon dioxide, which implies that it formed in a greatly colder region well beyond its parent stars. Thus, these compositions further support the theory that the origins of 3I/ATLAS lie in a stellar system that is quite alien compared to ours.
3I/ATLAS’s fleeting visit offers a rare window to study an interstellar comet
According to NASA, 3I/ATLAS reached its closest point to the Sun in late October 2025 and its closest point to Earth in December. As 3I/ATLAS is not a threat to Earth, its brief passage is considered a challenge for scientists.Following a predicted gravitational encounter in March 2026, the comet will again be ejected back into interstellar space. However, scientists believe that they only have a few hundred days to study the comet’s material properties and behaviour before this window of opportunity to unlock the secrets encoded in this cosmic relic of the early galaxy disappears back into the vast unknown. Despite the consensus that comet 3I/ATLAS is a natural comet, the comet has been surrounded by controversy. Avi Loeb, a Harvard University astrophysicist, proposes that certain properties of the comet–such as unexplained brightness patterns and what he refers to as the comet’s “anti-tail,” which points towards the Sun instead of away from the Sun–should be examined further.