Interstellar customer 3I/ATLAS might be the oldest comet we have ever seen

Is it a fowl? Is it a airplane? No, it’s a mysterious interstellar interloper noticed passing by way of our Solar System.

The comet, named 3I/ATLAS, was found by NASA’s Asteroid Terrestrial-impact Last Alert System (ATLAS) survey telescope.

Currently 675 million km (420 million miles) away, 3I/ATLAS might be the oldest comet ever seen. 

“Rather than the quiet Wednesday I had planned, I woke up to messages like ‘3I!!!!!!!!!!’,” says Matthew Hopkins, one of many astronomers who found the comet.

Hopkins and the group developed the Ōtautahi–Oxford mannequin to foretell the properties of interstellar objects primarily based on their orbits and attainable origins.

How outdated is 3I/ATLAS?

Non-interstellar comets, like Halley’s Comet, fashioned inside our Solar System and aren’t any older
than the Solar System’s 4.5-billion-year lifespan.

Interstellar guests, nonetheless, are usually not fashioned across the Sun and could be a lot older.

The group’s modelling suggests 3I/ATLAS is greater than seven billion years outdated – the oldest comet recognized so far. 

“It’s a fantastic opportunity to test our model on something brand new and possibly ancient,” Hopkins continues.

A customer from deep area

3I/ATLAS is simply the third-known interstellar object to have been noticed, following 2I/Borisov in 2019 and ‘Oumuamua in 2017.

Unlike its predecessors, it’s travelling on a a lot steeper path by way of the Galaxy, implying it originated in a very totally different area of the Milky Way. 

It’s thought the comet fashioned within the Milky Way’s ‘thick disc’, a area of historic stars that comprises about 10 per cent of our Galaxy’s stellar mass.

If it does originate from round an outdated star within the thick disc, that suggests that the comet needs to be wealthy in water-ice.

“This is an object from a part of the Galaxy we’ve never seen up close before,” says Professor Chris Lintott, who co-authored the research.

As 3I/ATLAS nears the Sun, its floor will warmth up, permitting scientists to look at whether or not the expulsion of vapour and dirt will type a basic glowing tail.

As effectively as having implications for the way we detect interstellar comets, astronomers additionally hope 3I/ATLAS will present clues in regards to the position of interstellar objects in star and planet formation inside our Galaxy.

Was Earth an interstellar wanderer?

Words: Chris Lintott

Five billion years in the past or so, one other interstellar object handed by way of our a part of the Galaxy.

This wanderer, maybe much like 3I/ATLAS, turned trapped within the nebula from which the Sun was forming.

Within the disc of fabric round our newly born star, the item started to accrete materials, rising rapidly right into a extra substantial physique – one that will change into the planet Earth.

Is this true?

Astronomers Suzanne Pfalzner and Michele Bannister proposed this concept following the arrival of ‘Oumuamua, and the romance of it grabbed me instantly.

Maybe the arrival of 3I will assist us perceive whether or not this concept about our cosmic origins holds up. 

This article appeared within the September 2025 subject of BBC Sky at Night Magazine