3I/ATLAS: Interstellar Comet May Be the Oldest Relic Ever Observed
A Rare Visitor From Interstellar Space
If you think our solar system is old, imagine something wandering into our cosmic neighborhood that formed long before Earth even existed. That's what astronomers believe they've found with interstellar comet 3I/ATLAS. First spotted on July 1, 2025, by the ATLAS survey telescope in Chile, this icy object has been darting toward the Sun at around 60 kilometers per second. This makes it just the third confirmed interstellar visitor we've ever caught—a true cosmic celebrity, right after 1I/ʻOumuamua and 2I/Borisov.
The catch? 3I/ATLAS could be the most ancient comet ever seen, possibly predating our entire solar system by millions of years. Nobody has ever gotten such a close look at something this old, so naturally, astronomers worldwide are eager to hunt for clues hidden in its trail of ice and dust.
Chasing Clues From the Galactic Center
3I/ATLAS isn't your typical comet. It first showed up in the data about 670 million kilometers from the Sun, already headed straight for the inner solar system. Astronomers dug into old data and found it had actually been visible since mid-June. This fast-moving comet will make its closest pass just inside Mars' orbit in October 2025, coming within 210 million kilometers of the Sun—safely far from Earth, thankfully.
Where did it come from? Its trajectory traces back to the constellation Sagittarius, near the dense, star-packed heart of the Milky Way. That region makes life tough for astronomers, thanks to the sheer number of stars in the background. Still, their calculations suggest a 66% chance that this object is even older than our solar system itself, which formed about 4.6 billion years ago.
Physically, estimates put 3I/ATLAS at a possible 20 kilometers across, but getting an exact measurement isn’t easy with something moving this fast and coming from so far away. Its icy composition hints that it formed around an ancient, cold star in the older part of the Milky Way that we call the thick disk—an area believed to be rich in water ice and primitive material from early in the galaxy’s history.
What’s particularly exciting? Interstellar visitors like this are cosmic time capsules. Studying their makeup helps scientists piece together what the galaxy looked like in its youth. Every time sunlight heats 3I/ATLAS and vaporizes its ices, hints about ancient interstellar chemistry are released for telescopes to capture before the comet slips out of view.
The spotlight is now on tracking 3I/ATLAS. As the comet swings closer to the Sun, leading teams like the ones led by Larry Denneau and Karen Meech are scrambling to gather as much data as they can before it becomes hidden by our star’s glare after September. International telescopes—including the big names like Gemini and the Southern Astrophysical Research Telescope—are all joining in, hoping to catch a detailed look before 3I/ATLAS disappears again until December. By then, astronomers hope to have gathered enough information to answer their big questions about just what this icy wanderer can teach us about our place in the cosmos.