The interstellar comet 3I/ATLAS has undergone an extraordinary transformation after spending billions of years traveling through the vast expanse of interstellar space. According to new findings based on data from the James Webb Space Telescope (JWST) and advanced computer simulations, the comet has developed a thick, irradiated crust that no longer resembles the composition of its original home star system. This revelation provides a groundbreaking look into how cosmic radiation can reshape interstellar objects over immense timescales.
Researchers found that 3I/ATLAS has been bombarded for billions of years by galactic cosmic rays—high-energy particles originating from outside our solar system. These cosmic rays have gradually altered the comet’s outer layers, fundamentally transforming its chemical and physical structure. The study, posted to the preprint server arXiv, suggests that this long exposure has given the comet a distinct identity, making it more a product of space radiation than a relic of its birthplace. The findings have yet to be peer-reviewed, but they mark a major step in understanding how interstellar visitors evolve.
The observations show that the surface of 3I/ATLAS, once rich in frozen gases and pristine material, is now coated in an irradiated shell up to 20 meters thick. This crust is the result of continuous bombardment from galactic cosmic rays over an estimated 7 billion years. As a result, what scientists are seeing today is a comet whose outer layers tell a story of endurance, transformation, and cosmic aging—a process that likely affects countless other interstellar bodies drifting between star systems.
The Long Journey of 3I/ATLAS
Discovered streaking through the solar system by astronomers using the Gemini South Telescope in Chile, comet 3I/ATLAS captured the scientific community’s attention with its unusual characteristics. Unlike typical comets originating within our solar system, 3I/ATLAS entered from interstellar space, marking it as only the third known interstellar object ever observed. Since its discovery, researchers have been eager to study its structure, composition, and trajectory to understand the mysteries of interstellar travel.
When observed through JWST’s Near-Infrared Spectrograph, 3I/ATLAS exhibited extremely high levels of carbon dioxide (CO2). Initially, scientists were puzzled by this enrichment, but further simulations showed that cosmic ray bombardment of carbon monoxide (CO) in the comet’s ice had gradually converted it into CO2. Without the protective shield of a heliosphere, as exists around our Sun, the comet was left exposed to the full brunt of interstellar radiation, reshaping its surface chemistry.
How Space Radiation Transforms a Comet
Galactic cosmic rays are streams of highly energetic protons and atomic nuclei that travel across the galaxy at near-light speeds. In our solar system, the Sun’s magnetic field and the heliosphere act as a buffer, shielding planets and comets from much of this radiation. However, interstellar comets like 3I/ATLAS have no such protection. Over billions of years, the continuous impact of these particles has deeply modified its ice, changing its structure down to depths of nearly 20 meters.
According to study lead author Romain Maggiolo from the Royal Belgian Institute for Space Aeronomy, the effect of cosmic radiation is slow but immensely powerful over geological timescales. Each collision between cosmic rays and the comet’s surface molecules triggers small-scale chemical reactions, gradually turning pristine ices into complex organic compounds and irradiated materials. The resulting outer crust now serves as a cosmic record of the harsh conditions of interstellar space.
A Paradigm Shift in Studying Interstellar Objects
The research team described their findings as a “paradigm shift” in how scientists interpret interstellar comets. Traditionally, such objects were thought to contain unaltered material from their parent star systems—pristine remnants that could offer clues to the environments in which they formed. But 3I/ATLAS challenges that assumption. The evidence indicates that its surface has been so thoroughly reprocessed by radiation that it no longer represents its original composition.
This means astronomers must approach interstellar studies differently, accounting for the possibility that many objects arriving from beyond our solar system may have undergone similar evolutionary processes. They may not be untouched messengers from other worlds but survivors—transformed and aged by cosmic exposure. This realization has far-reaching implications for our understanding of the galactic environment and how matter evolves across time and space.
The Comet’s Close Encounter with the Sun
3I/ATLAS recently reached its perihelion—its closest approach to the Sun—on October 29. As it approached, the heat from the Sun caused the comet’s outer layers to sublimate, releasing gases and forming its distinctive tail. However, researchers believe that the gases escaping during this phase come primarily from the irradiated outer shell, not from any untouched material beneath the surface. Only if solar erosion penetrates deeply enough might pristine ices from the comet’s core be revealed.
Maggiolo emphasized the importance of comparing observations made before and after perihelion to detect any compositional changes. If solar radiation manages to erode the surface significantly, it could expose layers that retain the original chemistry of the comet’s birth system. This would provide invaluable data about the building blocks of other star systems and the evolution of matter in interstellar space.
Tracing the Comet’s Origins and Movement
Since its discovery, 3I/ATLAS has been moving through the solar system at staggering speeds exceeding 130,000 mph (210,000 km/h). Its nearly straight and flat trajectory suggests that it was ejected from its home system billions of years ago, possibly after a gravitational interaction with a giant planet or a nearby star. Estimates indicate that 3I/ATLAS may be nearly 3 billion years older than our solar system, making it potentially the oldest comet ever observed.
Researchers used NASA’s JWST to capture infrared spectra of the comet, revealing unique features in its composition. These data were compared with earlier findings from NASA’s SPHEREx mission and prior models based on the European Space Agency’s Rosetta mission, which studied comet 67P. The results aligned closely, confirming that long-term cosmic irradiation plays a decisive role in shaping the outer structure of comets.
The Science Behind the Simulations
The team modeled how galactic cosmic rays affect the ice structure and chemical makeup of 3I/ATLAS over billions of years. Their simulations, based on laboratory experiments, showed that even 1 billion years of exposure was enough to produce an irradiated crust. Over longer timescales, the damage became extensive, leading to the thick, hardened shell now observed.
Although the researchers caution that lab conditions cannot perfectly replicate interstellar environments, their findings align with both theoretical predictions and JWST observations. The irradiated crust not only alters the comet’s appearance but also changes its physical properties, potentially influencing how it responds to solar heating, erosion, and gravitational forces.
The Legacy of 3I/ATLAS
Comet 3I/ATLAS represents a new frontier in the study of cosmic evolution. Once a frozen traveler from a distant star system, it now carries within its crust the story of interstellar survival. Its transformation reveals how radiation, time, and isolation sculpt the materials that drift between stars. For astronomers, it offers a living laboratory—a chance to study the effects of cosmic aging on matter and to understand the true nature of the galactic environment.
As 3I/ATLAS continues its journey, scientists will keep monitoring it using JWST and other telescopes. Whether or not future observations uncover pristine materials beneath its surface, the comet has already reshaped how we understand interstellar objects. Its irradiated crust stands as both a warning and a wonder: proof that time and cosmic radiation can erase the fingerprints of a world, leaving behind something entirely new and uniquely shaped by the universe itself.
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About the Author:
Harshit Raj
