Billions of Years of Radiation Altered a Comet
Comets are small, icy bodies that formed billions of years ago when planets were born. They travel around stars in stretched-out orbits. When they get close to a star, heat turns their ice into gas, creating bright heads and long tails. Most comets stay in the same star system forever. A few, however, come from completely different stars. These rare travelers are called interstellar comets.
Interstellar comets spend most of their lives in the cold, space between stars. They face constant attacks from high-speed particles known as galactic cosmic rays. These rays come from exploding stars and other violent events across the galaxy. Over billions of years, the rays slowly change the comet’s surface ice and dust. The changes build up layer by layer, like paint on an old wall.
Via Live Science
Only three interstellar objects have been confirmed in the solar system. The first, 1I/’Oumuamua, appeared in 2017. It looked like a dark rock with no tail. The second, 2I/Borisov, arrived in 2019 and acted more like a normal comet. The third, Comet 3I/ATLAS, showed up in 2025. Each new visitor gives scientists a chance to study material that formed around another star.
How Comet 3I/ATLAS Was Found
Astronomers discovered Comet 3I/ATLAS on July 1, 2025. The ATLAS survey telescopes in Chile spotted a faint point of light moving faster than anything in the solar system. Teams around the world pointed their telescopes at it to confirm the find. Within days, the path proved it was not bound to the Sun.
Via Space
The comet follows a hyperbolic orbit. This means it will pass through the solar system once and leave forever. Its speed tops 130,000 miles per hour. The orbit is almost straight compared to the looping paths of local comets. Older images from other surveys were found, pushing the first sighting back to May 2025.
The name 3I/ATLAS shows it is the third confirmed interstellar object. The “C” in C/2025 N1 (ATLAS) marks it as a comet. The solid core, called the nucleus, is probably less than 3.5 miles wide. Dust and gas clouds make the exact size hard to measure. The comet started releasing gas when it was still very far from the Sun, more than three times the distance of Earth.
Via Universe Space Tech
The Comet’s Path Through the Solar System
Comet 3I/ATLAS entered the solar system from the direction of the galaxy’s center. It flew past Mars in October 2025. It reached its closest point to the Sun on October 29, 2025, at about 1.36 times Earth’s distance. The brightness increased more than expected as it approached the Sun.
Special spacecraft watched the comet when it passed behind the Sun from Earth’s view. It will swing past Earth in December 2025 at a safe distance of 1.8 times Earth’s distance from the Sun. After that, it will head out past Jupiter in 2026 and never return.
Via Space
The comet grew a huge, cloudy head, called a coma, over 200,000 miles wide. It also formed tails of gas and dust. Water poured out like a giant hose, even at great distances. Other gases included cyanide and nickel vapor.
James Webb Space Telescope Observations
The James Webb Space Telescope observed the comet on August 6, 2025. It used a tool called the Near-Infrared Spectrograph to split the comet’s light into a rainbow of colors. Each color reveals different chemicals.
Via NASA Science
The telescope found the coma filled with carbon dioxide gas. The comet released about 129 kilograms of carbon dioxide every second. Water vapor, water ice grains, carbon monoxide, and carbonyl sulfide were also present. The amount of carbon dioxide compared to water was 7.6 times higher than normal. Typical comets in the solar system have a ratio of only 0.12.
Another NASA telescope named SPHEREx confirmed the findings soon after. The high carbon dioxide broke all known patterns. Water ice grains were tiny and lacked a regular crystal shape. The results puzzled scientists. They suggested the comet either formed very far from its home star or had been changed in a major way.
Via Astronomy Magazine
An Ancient Object from the Early Galaxy
Studies of the comet’s motion trace it back to the Milky Way’s thick disk. This region contains old stars with fewer heavy elements. The comet’s age is between 3 and 11 billion years, possibly around 7.6 billion years or more. The solar system is only 4.6 billion years old.
The comet likely formed far from a dim star, beyond the distance where carbon dioxide can freeze. A giant planet or a passing star probably kicked it out of its home system. It then wandered the galaxy for billions of years, constantly hit by cosmic rays. This makes the comet a sample of early galaxy chemistry, but one that has been heavily altered.
Via ESA/Webb
The first interstellar object, ’Oumuamua, was dark and dry. Some think it was a chunk of hydrogen or nitrogen ice changed by radiation. Borisov had large amounts of carbon monoxide, suggesting it formed in a very cold region. Comet 3I/ATLAS continues the pattern. All three known interstellar objects show signs of long exposure to space. Future visitors will probably have similar altered surfaces.
Strange Chemistry Raises Questions
Most comets release large amounts of water vapor when heated. Comet 3I/ATLAS had water ice but little water vapor at first. Something seemed to block heat from reaching deeper layers. The dust appeared reddish, a sign of complex organic material. Some common comet gases were missing.
Via Live Science
Nickel vapor appeared without iron, which is rare but has been seen in comets that pass very close to the Sun. The extreme amount of carbon dioxide stood out the most. In the solar system, comets with high carbon dioxide form beyond a certain distance from the Sun where carbon dioxide ice can freeze. For this interstellar comet, another process had to explain the abundance.
Galactic Cosmic Rays Change Ice Over Time
Galactic cosmic rays are tiny, fast-moving particles. They come from supernovas and other powerful events. In the solar system, the Sun’s magnetic field blocks most of these rays. Outside the Sun’s influence, comets face the full force. The rays smash into ice and break molecules apart. New molecules form from the pieces.
Via Vox
The rays also pack the ice tightly and create dark organic material on the surface. Over millions of years, the changes add up. After one billion years, the altered layer reaches 15 to 20 meters deep. After four or five billion years, almost all surface carbon monoxide disappears, replaced by carbon dioxide.
Building a Hard Outer Shell
Computer models matched the telescope data exactly. They showed a crust 50 to 65 feet thick, full of carbon dioxide and organic material. This crust acts like a tough shell that protects the inside. The strongest radiation effects happen at the surface. The dose drops quickly deeper down. Ice becomes dense and traps gases in odd ways. Extra particles created by the rays extend the changes a little farther.
Via dlr
Gas release removes very little material before the comet reaches the Sun, less than three feet. Even after the closest approach, erosion might remove only tens of meters at most. Scientists mainly see the processed crust, not the original interior. Researchers explained that the changes are slow but powerful over billions of years. Future studies must remove the effects of radiation to guess what the comet was like when it formed.
Why the Discovery Matters
The findings change how scientists think about objects from other star systems. These comets are not perfect records of their birthplaces. The galaxy itself reshapes them over time. Cosmic rays act like weather in space, wearing down surfaces.
Via Futurism
Researchers now need to subtract the effects of the crust to learn about the original material. The extra step makes the work harder, but also reveals how chemistry works across the galaxy. The comet proves that small-scale lab tests can predict changes over billions of years in real space.
Plans for More Observations
Additional James Webb observations are scheduled after the comet passes the Sun. A different instrument will look for complex organic molecules. The Hubble Space Telescope studied the comet in November 2025 to measure sulfur compounds.
Via Earth
If large amounts of material erode away, fresh ice from deeper inside might appear. This would let scientists compare processed and unprocessed layers. Spacecraft near Mars took images during the flyby. Monitoring will continue as the comet moves away. A new large survey telescope called Rubin Observatory may soon find more interstellar objects.
What the Comet Teaches Us
Comet 3I/ATLAS shows how the harsh environment of space can transform even the most frozen objects. The thick crust built by radiation hides the comet’s original makeup. The discovery highlights the power of slow change over vast time.
Via Live Science
A comet that started as a simple ball of ice became a complex, layered body during its long journey. Scientists now have a better map of how cosmic rays affect small bodies. This knowledge will help interpret future interstellar visitors.
Explore the James Webb’s Findings on a Strange Comet
Comet 3I/ATLAS started as a simple icy body around a distant star. Billions of years of radiation turned its surface into a thick, complex crust. The James Webb Space Telescope revealed this hidden transformation.
Via Live Science
The comet reminds people that nothing in space stays the same forever. Even the coldest objects face constant change. As it speeds away from the solar system, it carries lessons about the galaxy’s power to reshape the small and the ancient.
The discovery opens new questions about the chemistry of the early universe. It shows how the space between stars is not empty but active. Future visitors will build on this knowledge, helping humans understand the place in a vast, changing cosmos.
