Interstellar object that invaded our solar system might be the 'oldest ever seen'

Astronomers often search the skies for the familiar. Planets, moons, comets. But in early July 2025, something entirely unexpected arrived. The discovery sparked excitement and awe. A mysterious object, likely older than our solar system, made its presence known. This was no ordinary comet. Its name? 3I/ATLAS.

This comet’s journey has been billions of years in the making. Its story may rewrite what we know about the galaxy’s ancient building blocks. The discovery didn’t just add a new name to the comet list. It unlocked a time capsule from a part of the Milky Way we have never seen up close.

3I/ATLAS might be the oldest comet ever seen. Older than the Sun, the planets, and every familiar object in our celestial backyard.

Ancient comet enters our solar system

3I/ATLAS is only the third object ever spotted entering our solar system from interstellar space. Unlike the famous 1I/’Oumuamua in 2017 and 2I/Borisov in 2019, this new arrival may hold secrets from even deeper in time.

Its trajectory is unlike the others. It is not held on track by the Sun’s gravity and is on a steep path through the galaxy that hints at a unique origin.

The object appears to come from the Milky Way’s thick disk, an area populated by some of the galaxy’s oldest stars. These stars orbit above and below the thin disk where our Sun resides. This region has remained mostly unexplored by astronomers until now.

“All non-interstellar comets, such as Halley’s Comet, formed with our solar system, so are up to 4.5 billion years old,” said Matthew Hopkins, astronomer at the University of Oxford.

“But interstellar visitors have the potential to be far older and, of those known about so far, our statistical method suggests that 3I/ATLAS is very likely to be the oldest comet we have ever seen.”

3I/ATLAS may be older than the Sun

What makes this object even more compelling is its composition. Hopkins and his team believe 3I/ATLAS likely formed around a thick-disk star. This leads them to think it is rich in water ice.

That would be significant. It points to conditions that existed long before our solar system was born.

The comet was first spotted by the ATLAS survey telescope in Chile. It appeared when it was 670 million kilometres from the Sun. Since then, astronomers have watched it closely. It has already begun to show signs of activity.

“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 the 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.”

Comet shows gas and dust activity

As 3I/ATLAS moves closer to the Sun, its frozen surface begins to react. Sunlight warms the surface, triggering what astronomers call cometary activity. Ice turns to vapour, releasing gas and dust. A glowing coma forms, followed by a tail.

These signs are already visible. It is possible that 3I/ATLAS could be larger than the two earlier interstellar comets.

That scale makes a difference. It improves the chance that telescopes can study the object in detail. Already, some of the most powerful observatories are watching the comet as it awakens.

“We’re in an exciting time: 3I is already showing signs of activity. The gases that may be seen in the future as 3I is heated by the Sun will test our model,” said Dr Michele Bannister, of the University of Canterbury in New Zealand.

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

More like 3I/ATLAS

The timing of 3I/ATLAS’s appearance could not be more perfect. It came just as researchers were preparing the Vera C. Rubin Observatory for its survey operations. This new telescope, designed for sweeping sky scans, could detect many more interstellar objects.

Until now, such objects have been rare. That may soon change.

The discovery gives researchers hope that Rubin could detect between 5 and 50 more such visitors over the next decade. If some are as large and bright as 3I/ATLAS, they could reveal even more about ancient galactic regions.

“The solar system science community was already excited about the potential discoveries Rubin will make in the next 10 years, including an unprecedented number of interstellar objects,” said co-researcher Dr. Rosemary Dorsey, of the University of Helsinki.

“The discovery of 3I suggests that prospects for Rubin may now be more optimistic; we may find about 50 objects, of which some would be similar in size to 3I. This week’s news, especially just after the Rubin First Look images, makes the upcoming start of observations all the more exciting.”

Predicting the unknown

Hopkins developed a model during his doctoral research to simulate how interstellar objects behave based on their orbits and stellar origins. Named the Ōtautahi–Oxford Model, it was ready just in time for this discovery.

Hopkins had just finished defending his thesis when the news broke. He was planning a quiet holiday, but fate had other plans.

“Rather than the quiet Wednesday I had planned, I woke up to messages like ‘3I!!!!!!!!!!’,” related Hopkins. “It’s a fantastic opportunity to test our model on something brand new and possibly ancient.”

This marked the first real-time use of predictive modelling on an interstellar comet. Matching predictions to actual data gives the team confidence in their approach. It may also help guide future discoveries.

You can see 3I/ATLAS from Earth

For those hoping to see 3I/ATLAS with their own eyes, there is good news. The comet should become visible through amateur telescopes by late 2025 or early 2026.

Though it will not be as dramatic as some comets that pass close to Earth, its uniqueness makes it special.

This is a chance to look into the past. Possibly seven billion years into the past. As its glow becomes clearer, it carries with it the story of stars and planets long gone.

3I/ATLAS reminds us that the galaxy is full of untold stories. They drift silently through space, waiting for the right moment to be seen.

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates. 

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–