Interstellar comet 3I/ATLAS has made a striking appearance in our solar system, recently observed by the Gemini South telescope in Chile on August 27. This comet has shown to be significantly altered by cosmic radiation through billions of years of its journey across the Milky Way, as revealed by new research conducted with the James Webb Space Telescope (JWST).
Over an estimated lifespan of 7 billion years, comet 3I/ATLAS has absorbed an enormous amount of galactic cosmic rays, leading to the formation of a deeply irradiated crust that deviates sharply from the original composition of its home star system. The study, which has been shared on the preprint server arXiv but has not yet undergone peer review, indicates that the comet’s “extreme” carbon dioxide (CO2) levels are a result of alterations caused by these cosmic rays.
Galactic cosmic rays, consisting of high-energy particles from beyond our solar system, transform carbon monoxide (CO) into CO2 upon striking it in space. In the heliosphere surrounding our solar system, the Sun’s radiative influence protects planets from most cosmic radiation; however, this protective barrier is absent in interstellar space, where comet 3I/ATLAS has spent a substantial portion of its existence.
The researchers, led by Romain Maggiolo from the Royal Belgian Institute for Space Aeronomy, concluded that the physical state of the comet’s ices has been extensively altered to a depth of approximately 50 to 65 feet (15 to 20 meters). Maggiolo remarked, “It’s very slow, but over billions of years, it’s a very strong effect.”
These findings represent a significant shift in how scientists study interstellar objects, suggesting that they are primarily composed of materials processed by cosmic radiation rather than untouched material that reflects their origins.
Comet 3I/ATLAS is currently on a trajectory around the sun, having reached its closest approach (perihelion) on October 29. As it nears the sun, the comet heats up, causing the ices on its surface to release gas. The researchers speculate that the gases emitted from the comet before perihelion were primarily from its irradiated surface. After perihelion, solar erosion might expose the original materials within the comet, offering potential insight into its initial composition.
Since its discovery in July, astronomers have been eager to study 3I/ATLAS, which is traveling through the solar system at speeds exceeding 130,000 mph (210,000 km/h). Some studies even suggest that it may be the oldest comet ever observed, potentially around 3 billion years older than our own solar system.
Additionally, this new research enhances previous studies that identified the comet’s rich CO2 content based on observations from JWST and NASA’s SPHEREx orbiter. Maggiolo and his team adapted models originally used to study the irradiation of domestic comets to apply to 3I/ATLAS, merging laboratory experiments with simulations to understand the long-term effects of cosmic radiation.
The implications of these findings are vast, providing researchers with a better understanding of the aging processes that interstellar comets undergo. While the changes in 3I/ATLAS present challenges for scientific analysis, it continues to offer fascinating insights into the nature of these ancient celestial wanderers.