The James Webb Space Telescope has observed something rather fascinating about 3I/ATLAS, the third interstellar visitor to our solar system. Not just JWST, but Spectro-Photometer for the History of the Universe, Epoch of Reionisation, and Ices Explorer (SPHEREx) have also noticed how the ratio of carbon dioxide to water in the comet’s coma is not normal. “The ratio measured for the amount of CO2 gas relative to H2O is among the highest ever observed in a solar system comet, demonstrating that the coma of 3I/ATLAS is very CO2-rich,” NASA said some time back. “This may indicate that 3I/ATLAS was exposed to higher levels of radiation than comets from inside the solar system or that it formed in a region of its original planetary disk where CO2 ice naturally freezes out from the gas,” it added. Now, a new study has also pointed out that the comet is a battered and bruised version of itself following billions of years of interstellar journey.
Two theories that did not explain the odd CO2 and water ratio in 3I/ATLAS
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A team of astronomers from Belgium and the USA studied the composition of 3I/ATLAS and posted the findings on the preprint server arXiv. They tried to explain the odd ratios seen by JWST and others, and why they were observed when the object was so far from the radiation of our Sun. “JWST/NIRSpec measurements show CO2/H2O = 7.6 ± 0.3, placing 3I/ATLAS 4.5σ above solar system trends at the observed heliocentric distance,” the authors wrote in the paper. Two of their hypotheses did not fit the bill – Either the protoplanetary disks where it originated had certain physical conditions that could alter carbon monoxide and carbon dioxide presence, or Co was destroyed mid-plane in the protoplanetary disk, causing CO2 to spike.
3I/ATLAS is hiding original material inside
The one that explained it aptly was the galactic cosmic ray (GCR) processing. Under this, galactic cosmic rays converted carbon monoxide into carbon dioxide. This led to the creation of an organic-rich, irradiated crust on the comet’s nucleus over a billion years. “Laboratory experiments demonstrate that GCR irradiation efficiently converts CO to CO2 while synthesising organic-rich crusts, suggesting that the outer layers of 3I/ATLAS consist of irradiated material whose properties are consistent with the observed composition of 3I/ATLAS coma and with its observed spectral reddening,” the authors wrote. The outgassing data show that the material inside the comet remains untouched.
What does this discovery mean?
If this is true for 3I/ATLAS and other interstellar objects, then it means humans would never be able to use them to study other star systems. “Rather than being pristine messengers from distant planetary systems, interstellar objects may instead carry signatures of processed material shaped by Gyr-scale cosmic-ray exposure,” the paper states. These changes could have happened in their “parent stellar systems, prior to ejection, and during their interstellar transit to the solar system.”
So, while the original material sits carefully cocooned inside the outer shell, what we are able to see are the scars it endured during its trip and not its true self.