Comet 3I/ATLAS found may be the earliest one ever discovered in space

In the vast expanse of the Milky Way, a new visitor has arrived. The comet 3I/ATLAS, discovered by NASA's Asteroid Terrestrial-impact Last Alert System (ATLAS) survey telescope, is not a native of our Solar System. Instead, it is thought to have originated from the Milky Way's 'thick disc', a region of ancient stars that contains about 10 per cent of our Galaxy's stellar mass.

This interstellar visitor is much older than non-interstellar comets like Halley's Comet, with an estimated age of over seven billion years. This makes 3I/ATLAS the oldest comet identified to date, about three billion years older than the Solar System.

The discovery of 3I/ATLAS has sparked excitement among astronomers. Chris Lintott, one of the scientists involved in the discovery, expressed his enthusiasm, stating, "It's a fantastic opportunity to test our model on something brand new and possibly ancient."

The romance of the idea that Earth was once an interstellar wanderer was initially proposed by astronomers Suzanne Pfalzner and Michele Bannister following the arrival of 'Oumuamua. The arrival of 3I/ATLAS may help astronomers understand whether this idea about Earth's cosmic origins holds up.

If 3I/ATLAS originated from an old star in the thick disc, it could be rich in water-ice, offering valuable insights into the formation of planets in different regions of the Milky Way. As 3I/ATLAS nears the Sun, its surface will heat up, allowing scientists to observe the expulsion of vapour and dust, potentially forming a glowing tail.

Currently, 3I/ATLAS is approximately 675 million km (420 million miles) away, making it an exciting prospect for astronomers worldwide. Unlike its predecessors, 3I/ATLAS is travelling on a much steeper path through the Galaxy, implying it originated in a completely different region of the Milky Way.

As we welcome 3I/ATLAS into our Solar System, it presents a unique opportunity to learn more about the Milky Way's history and the role of interstellar objects in star and planet formation within our Galaxy. This article about 3I/ATLAS appeared in the September 2025 issue of our website.