The just lately found interstellar customer 3I/ATLAS could also be one of many oldest comets ever seen by humanity.
The item was already thrilling to astronomers as solely the third area object seen coming into the photo voltaic system from past its limits, the opposite two being 1I/’Oumuamua seen in 2017 and 2I/Borisov detected in 2019.
Nonetheless, new analysis has proven this doubtlessly “water ice-rich” customer may very well be much more extraordinary than initially believed. 3I/ATLAS may very well be round 3 billion years older than our 4.5 billion-year-old photo voltaic system and thus any comet ever earlier than noticed.
College of Oxford astronomer Matthew Hopkins is a part of a group of scientists that assume 3I/ATLAS, found on July 1, 2025 by the ATLAS survey telescope, is round 7 billion years outdated.
“All non-interstellar comets, akin to Halley’s comet, shaped similtaneously our photo voltaic system, so they’re as much as 4.5 billion years outdated,” Hopkins stated in a press release. “However interstellar guests have the potential to be far older, and of these identified about to this point, our statistical methodology means that 3I/ATLAS could be very more likely to be the oldest comet we’ve ever seen.”
The key to 3I/ATLAS’ outdated age
The important thing to the superior age of 3I/ATLAS is the truth that it comes from a very completely different area of the Milky Manner than earlier interstellar guests.
Primarily based upon the steep trajectory that 3I/ATLAS seems to be taking by means of our galaxy, Hopkins and colleagues theorize that it originated within the Milky Manner’s “thick disk” of stars.
The thick disk is a band of our galaxy’s most historic stars that sandwiches the skinny disk, which shaped extra just lately and accommodates our comparatively younger star, the solar, and the photo voltaic system.
“That is an object from part of the galaxy we have by no means seen up shut earlier than,” College of Oxford astrophysicist Chris Lintott stated. “We expect there is a two-thirds likelihood this comet is older than the photo voltaic system, and that it has been drifting by means of interstellar area ever since.”
If 3I/ATLAS originates from the Milky Manner’s thick stellar disk, and thus shaped round an historic star, this additionally has implications for its chemical composition. Hopkins and crew counsel the interstellar interloper could also be wealthy in water ice.
As 3I/ATLAS will get nearer to the solar, it’s going to get hotter. Frozen ices will flip to gasoline, a course of known as sublimation, and erupt from the floor of the comet.
This outgassing will give 3I/ATLAS a cometary aura, or “coma,” and a brilliant tail, the acquainted and distinctive traits of comets.
Observations have already indicated that 3I/ATLAS is bursting to life with cometary exercise. These observations additionally appear to point that 3I/ATLAS is greater than earlier interstellar invaders 1I/’Oumuamua and 2I/Borisov.
“We’re in an thrilling time, 3I/ATLAS is already exhibiting indicators of exercise. The gases which may be seen sooner or later as 3I/ATLAS is heated by the solar will take a look at our mannequin,” group member Michele Bannister, of the College of Canterbury in New Zealand, stated. “A number of the largest telescopes on the earth are already observing this new interstellar object – considered one of them might be able to discover out!”
One of many telescopes that will probably be attempting to get a take a look at 3I/ATLAS would be the Vera C. Rubin Observatory.
In truth, this interstellar customer was first noticed as scientists had been getting ready to make observations with Rubin, which they predict will uncover between 5 and 50 interstellar objects passing by means of the photo voltaic system because it conducts the 10-year-long Legacy Survey of Area and Time (LSST).
“The invention of 3I/ATLAS means that prospects for Rubin might now be extra optimistic; we might discover about 50 objects, of which some could be comparable in dimension to 3I/ATLAS.
“This week’s information, particularly simply after the Rubin First Look photos, makes the upcoming begin of observations all of the extra thrilling.”
The mannequin the group used to analyze the origins of 3I/ATLAS was developed by Hopkins as a part of his doctoral thesis, one he defended only one week earlier than the interstellar object was found.
Somewhat than heading on trip, Hopkins discovered himself making use of the mannequin, dubbed the Ōtautahi–Oxford Mannequin, in real-time for the primary time. The take a look at topic: 3I/ATLAS.
“Somewhat than the quiet Wednesday I had deliberate, I woke as much as messages like ‘3I!’ It is a improbable alternative to check our mannequin on one thing model new and probably historic,” Hopkins concluded.
Hopkins mentioned the 3I/ATLAS findings on Friday (June 11) on the Royal Astronomical Society Nationwide Astronomy Assembly (NAM) 2025 at Durham College within the UK.
