Key Takeaways:

• Comet 3I/ATLAS is only the third known interstellar object observed passing through our Solar System.
• This mysterious comet likely originated from the Milky Way’s “thick disk,” a region home to some of the galaxy’s oldest stars.
• If confirmed, 3I/ATLAS could be over 7 billion years old, making it older than our 4.6-billion-year-old Solar System.
• Astronomers are closely monitoring the comet as it approaches the Sun, which may reveal secrets about early galactic chemistry.

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A Rare Interstellar Visitor

Astronomers have identified a remarkable interstellar comet that may be the oldest ever observed—possibly predating our Solar System by billions of years.

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Dubbed 3I/ATLAS, this icy wanderer is only the third confirmed interstellar object to enter our cosmic neighborhood, following 1I/’Oumuamua (2017) and 2I/Borisov (2019). However, unlike its predecessors, this comet appears to have originated from a completely different part of the Milky Way—the “thick disk,” a region populated by ancient stars.

The discovery, led by University of Oxford astronomer Matthew Hopkins, was presented at the Royal Astronomical Society’s National Astronomy Meeting 2025 in Durham. His team’s findings suggest that 3I/ATLAS could be over 7 billion years old, making it a relic from a time long before our Sun and planets formed.

What Makes This Comet So Special?

Most comets in our Solar System, like Halley’s Comet, formed alongside it roughly 4.6 billion years ago. However, interstellar visitors like 3I/ATLAS have the potential to be far older, having drifted through the galaxy for billions of years before reaching us.

Hopkins explains:

*”All non-interstellar comets formed with our Solar System, so they’re up to 4.5 billion years old. But interstellar visitors have the potential to be far older—and our statistical method suggests that 3I/ATLAS is very likely the oldest comet we’ve ever seen.“*

A Journey from the Milky Way’s Thick Disk

What sets 3I/ATLAS apart is its unusual trajectory. Unlike ‘Oumuamua and Borisov, which came from the galaxy’s star-filled plane, this comet appears to have originated from the Milky Way’s thick disk—a sparsely populated region where stars orbit above and below the galactic plane.

“This is an object from a part of the galaxy we’ve never seen up close before,” said Professor Chris Lintott, co-author of the study and presenter of BBC’s The Sky at Night.
“We think there’s a two-thirds chance this comet is older than the Solar System, and that it’s been drifting through interstellar space ever since.”

How Was 3I/ATLAS Discovered?

The comet was first detected on 1 July 2025 by the ATLAS (Asteroid Terrestrial-impact Last Alert System) survey telescope in Chile, when it was about 670 million kilometers from the Sun. Follow-up observations confirmed its interstellar origins, and astronomers worldwide are now tracking its approach.

What Will Happen as It Nears the Sun?

As 3I/ATLAS moves closer to the Sun, solar heating will cause its icy surface to vaporize, creating a glowing coma (atmosphere) and tail—classic features of an active comet. Early signs suggest it is already outgassing, and it may be larger than its interstellar predecessors.

Dr. Michele Bannister, a co-author from the University of Canterbury in New Zealand, said:

“We’re in an exciting time: 3I is already showing signs of activity. The gases we detect as it heats up will test our model of its origins.”

Why Does This Discovery Matter?

1. Understanding Galactic History: If confirmed, 3I/ATLAS could provide insights into the chemical composition of the early Milky Way, helping astronomers piece together how our galaxy evolved.
2. Future Discoveries: Upcoming telescopes like the Vera C. Rubin Observatory may detect more such objects, revealing how common ancient interstellar comets are.
3. Planetary Formation Clues: Some scientists believe interstellar comets could have delivered water and organic molecules to young star systems, possibly aiding the emergence of life.

What’s Next?

Astronomers worldwide are training powerful telescopes on 3I/ATLAS, hoping to analyze its composition as it becomes more active. The findings could reshape our understanding of interstellar objects and their role in the cosmos.

“Some of the biggest telescopes in the world are already observing this new interstellar object—one of them may be able to find out!” said Dr. Bannister.

As scientists continue to study this celestial time capsule, one thing is clear: 3I/ATLAS is unlike anything humanity has ever seen—and its secrets may rewrite what we know about the universe.