11.07.2025
ESO's Very Large Telescope (VLT) has obtained new images of the path, shown as a dotted line of lights, of 3I/Atlas, an interstellar object discovered last week
A mystery interstellar object spotted last week by astronomers could be the oldest comet ever seen, according to scientists.
Named 3I/Atlas, it may be three billion years older than our own solar system, suggests the team from Oxford university.
It is only the third time we have detected an object that has come from beyond our solar system.
The preliminary findings were presented on Friday at the national meeting of the UK's Royal Astronomical Society in Durham.
"We're all very excited by 3I/Atlas," University of Oxford astronomer Matthew Hopkins told BBC News.
"I've just finished my PhD where I spent four years predicting the discovery of [more] interstellar objects, and then for the first time in my studies, we found one," he said.
Based on the object's speed, Mr Hopkins says it could be more than seven billion years old, and it may be the most remarkable interstellar visitor yet.
3I/Atlas was first spotted on 1 July 2025 by the Atlas survey telescope in Chile, when it was about 670 million km from the Sun.
It is currently visible only with very large telescopes, and it is about the distance of Jupiter from Earth.
Since then astronomers around the world have been racing to identify its path and discover more details about it.
Mr Hopkins believes it originated in the Milky Way's "thick disk". This is a group of ancient stars that orbit above and below the area where the Sun and most stars are located.
The top view of the Milky Way, below, gives a sense of the object's path around our galaxy. The estimated orbits of 3I/Atlas are in red and those of our Sun are in yellow.
The estimated orbits around the Milk Way of the object, in red, and our Sun, in yellow
The team believe that because 3I/Atlas probably formed around an old star, it is made up of a lot of water ice.
That means that as it approaches the Sun later this year, the energy from the Sun will heat the object's surface, leading to blazes of vapour and dust.
That could create a glowing tail.
The researchers made their findings using a model developed by Mr Hopkins.
"This is an object from a part of the galaxy we've never seen up close before," said Prof Chris Lintott, co-author of the study.
"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."
Interstellar objects form around other stars, at the start of those stars' lives, explains Mr Hopkins.
"This connection back to their parent stars means that we can look at the stellar population of the Milky Way," he adds.
Later this year, 3I/Atlas should be visible from Earth using amateur telescopes.
Before 3I/Atlas soared into view, just two others had been seen. One was called 1I/'Oumuamua, found in 2017 and another called 2I/Borisov, discovered in 2019.
Astronomers globally are currently gearing up to start using a new, very powerful telescope in Chile, called the Vera C Rubin.
When it starts fully surveying the southern night sky later this year, scientists expect that it could discover between five and 50 new interstellar objects.
Quelle: BBC
+++
Astronomers say new interstellar visitor 3I/ATLAS is 'very likely to be the oldest comet we have ever seen'
"This is an object from a part of the galaxy we've never seen up close before."
The recently discovered interstellar visitor 3I/ATLAS may be one of the oldest comets ever seen by humanity.
The object was already exciting to astronomers as only the third space object seen entering the solar system from beyond its limits, the other two being 1I/'Oumuamua seen in 2017 and 2I/Borisov detected in 2019.
However, new research has shown this potentially "water ice-rich" visitor could be even more extraordinary than initially believed. 3I/ATLAS could be around 3 billion years older than our 4.5 billion-year-old solar system and thus any cometever before observed.
University of Oxford astronomer Matthew Hopkins is part of a team of scientists that think 3I/ATLAS, discovered on July 1, 2025 by the ATLAS survey telescope, is around 7 billion years old.
"All non-interstellar comets, such as Halley's comet, formed at the same time as our solar system, so they are up to 4.5 billion years old," Hopkins said in a statement. "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."
The secret to 3I/ATLAS' old age
The key to the advanced age of 3I/ATLAS is the fact that it comes from a completely different region of the Milky Way than previous interstellar visitors.
Based upon the steep trajectory that 3I/ATLAS appears to be taking through our galaxy, Hopkins and colleagues theorize that it originated in the Milky Way's "thick disk" of stars.
The thick disk is a band of our galaxy's most ancient stars that sandwiches the thin disk, which formed more recently and contains our relatively young star, the sun, and the solar system.
"This is an object from a part of the galaxy we've never seen up close before," University of Oxford astrophysicist Chris Lintott said. "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."
If 3I/ATLAS originates from the Milky Way's thick stellar disk, and thus formed around an ancient star, this also has implications for its chemical composition. Hopkins and crew suggest the interstellar interloper may be rich in water ice.
As 3I/ATLAS gets closer to the sun, it will get warmer. Frozen ices will turn to gas, a process called sublimation, and erupt from the surface of the comet.
This outgassing will give 3I/ATLAS a cometary aura, or "coma," and a bright tail, the familiar and distinctive characteristics of comets.
Observations have already indicated that 3I/ATLAS is bursting to life with cometary activity. These observations also seem to indicate that 3I/ATLAS is bigger than previous interstellar invaders 1I/'Oumuamua and 2I/Borisov.
"We're in an exciting time, 3I/ATLAS is already showing signs of activity. The gases that may be seen in the future as 3I/ATLAS is heated by the sun will test our model," team member Michele Bannister, of the University of Canterbury in New Zealand, said. "Some of the biggest telescopes in the world are already observing this new interstellar object – one of them may be able to find out!"
Stacked images of interstellar comet 3I/ATLAS taken by ESO's Very Large Telescope (VLT) on July 8, 2025. (Image credit: ESO/O. Hainaut)
One of the telescopes that will be trying to get a look at 3I/ATLAS will be the Vera C. Rubin Observatory.
In fact, this interstellar visitor was first spotted as scientists were preparing to make observations with Rubin, which they predict will uncover between 5 and 50 interstellar objects passing through the solar system as it conducts the 10-year-long Legacy Survey of Space and Time (LSST).
"The discovery of 3I/ATLAS 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/ATLAS.
"This week's news, especially just after the Rubin First Look images, makes the upcoming start of observations all the more exciting."
The model the team used to investigate the origins of 3I/ATLAS was developed by Hopkins as part of his doctoral thesis, one he defended just one week before the interstellar object was discovered.
Rather than heading on vacation, Hopkins found himself applying the model, dubbed the Ōtautahi–Oxford Model, in real-time for the first time. The test subject: 3I/ATLAS.
"Rather than the quiet Wednesday I had planned, I woke up to messages like '3I!' It's a fantastic opportunity to test our model on something brand new and possibly ancient," Hopkins concluded.
Hopkins discussed the 3I/ATLAS findings on Friday (June 11) at the Royal Astronomical Society National Astronomy Meeting (NAM) 2025 at Durham University in the UK.
Quelle: SC