The photo voltaic system’s latest customer, 3I/ATLAS, could also be 3 billion years older than the solar and its planets.
First found on July 1, 3I/ATLAS is a uncommon interstellar object — solely the third ever noticed. Since then, astronomers have been racing to uncover its origins. A brand new calculation predicts that 3I/ATLAS originated from part of the Milky Means known as the thick disk. If that’s the case, there’s a two-thirds probability that it’s a comet over 7 billion years outdated. That will make it the oldest comet identified, researchers reported July 11 on the Royal Astronomical Society’s Nationwide Astronomy Assembly 2025 in Durham, England.
Interstellar objects don’t include “a label you can simply learn,” says research coauthor Chris Lintott, an astrophysicist on the College of Oxford. “All we actually know is the path it’s coming in, and to go from that to say something in regards to the age is actually rewarding.”
Others warning that extra knowledge are required to verify the thing’s origin and age.
With regards to origin, “it may have been an amazingly fortunate object that encountered nothing,” says Pamela Homosexual, an astronomer with the Planetary Science Institute, headquartered in Tucson, Ariz. “On the similar time, it may have had its orbit modified dozens of instances via encounters with different photo voltaic techniques or rogue planets.” Or, it even may have come from someplace nearer alongside the identical trajectory, she provides.
Lintott agrees that extra proof is required. However as a result of 3I/ATLAS’s velocity is typical for an interstellar object, he says, “we might be fairly positive it hasn’t encountered one other star.” He provides that 3I/ATLAS is shifting up and down within the galactic aircraft, which occurs when one thing has been within the thick disk of historical stars above and beneath the galaxy’s skinny aircraft for a very long time — bolstering the speculation that 3I/ATLAS is outdated and originated there.
Underpinning the prediction is a chance simulator for learning interstellar objects, Lintott and colleagues additionally report in a paper submitted July 7 to arXiv.org. Extrapolating from the measured positions and velocities of roughly a billion stars noticed by the Gaia satellite tv for pc, the simulator fashions the trajectories of each star within the Milky Means, each dwelling and lifeless, and consists of their possible asteroids and comets. Combining this simulation with precise telescope knowledge, researchers can then predict the place an interstellar object got here from — and primarily based on the age and composition of the celebrities there, the properties of the thing too.
Making use of the mannequin to 3I/ATLAS suggests the customer got here from the Milky Means’s thick disk. If it did type there, the relative lack of heavy parts in these stars means the comet might be wealthy in water, versus rock or mud.
Composition knowledge will assist relaxation the case, each Homosexual and Lintott say. Within the coming weeks, daylight will set off outgassing, revealing vapor and dirt signatures. Specifically, astronomers might be desperate to measure its water abundance and elemental make-up, which may assist confirm whether or not 3I/ATLAS got here from an outdated, thick-disk star.
Till then, 3I/ATLAS’s origin stays a guessing sport. “It’s like Wheel of Fortune,” Homosexual says. “We have now 4 letters out of 20 proper now, and somebody may be capable to guess the complete phrase, however they is also very incorrect.”
