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 Approach referred to as the thick disk. In that case, there’s a two-thirds likelihood that it’s a comet over 7 billion years previous. 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 which you can simply learn,” says research coauthor Chris Lintott, an astrophysicist on the College of Oxford. “All we actually know is the course it’s coming in, and to go from that to say something concerning the age is admittedly rewarding.”
Others warning that extra information are required to verify the article’s origin and age.
Relating 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 identical time, it may have had its orbit modified dozens of instances by 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 will be moderately positive it hasn’t encountered one other star.” He provides that 3I/ATLAS is transferring up and down within the galactic aircraft, which occurs when one thing has been in the thick disk of historic stars above and beneath the galaxy’s skinny aircraft for a very long time — bolstering the speculation that 3I/ATLAS is previous 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 Approach, each dwelling and useless, and consists of their possible asteroids and comets. Combining this simulation with precise telescope information, researchers can then predict the place an interstellar object got here from — and based mostly on the age and composition of the celebs there, the properties of the article too.
Making use of the mannequin to 3I/ATLAS suggests the customer got here from the Milky Approach’s thick disk. If it did kind there, the relative lack of heavy parts in these stars means the comet might be wealthy in water, versus rock or mud.
Composition information will assist relaxation the case, each Homosexual and Lintott say. Within the coming weeks, daylight will set off outgassing, revealing vapor and mud signatures. Particularly, astronomers shall be wanting to measure its water abundance and elemental make-up, which may assist confirm whether or not 3I/ATLAS got here from an previous, thick-disk star.
Till then, 3I/ATLAS’s origin stays a guessing recreation. “It’s like Wheel of Fortune,” Homosexual says. “We now have 4 letters out of 20 proper now, and somebody may be capable of guess your entire phrase, however they is also very incorrect.”
