The mysterious object speeding through our solar system may be even more unique than many scientists originally thought.
New scans of the interstellar visitor known as 3I/ATLAS have found that it is likely an unusual comet that’s much smaller than it previously appeared and is unexpectedly releasing loads of carbon dioxide gas (CO2).
The large amount of CO2 pouring out, about 940 trillion molecules per second, is a major finding, suggesting 3I/ATLAS formed in a star system that doesn’t look anything like ours, where comets are much different than the ones we see orbiting our sun.
Based on all the light coming from 3I/ATLAS, scientists originally suspected the object was more than 12 miles in diameter.
Now, NASA‘s most powerful telescopes have cut that estimate down to 1.7 miles. The comet seemed larger because over 99 percent of the light observed came from a large, bright cloud of dust and gas surrounding it, called a coma. 3I/ATLAS is currently about 298 million miles from Earth.
Not only is the interstellar object much smaller, but a new study by NASA’s SPHEREx telescope has discovered that 3I/ATLAS is releasing a large amount of carbon dioxide gas (CO2) and is covered in water ice.
This makes it unlike the vast majority of comets seen because most of its brightness comes from the cloud of dust around it, not its solid core.
The comet also doesn’t show much water vapor or carbon monoxide gas being released, which is very unusual for comets traveling this close to our sun.
The interstellar object known as 3I/ATLAS is now believed to be a unique comet that’s releasing tons of carbon dioxide gas
A NASA study found that the object is not 12 miles in diameter as originally thought. It’s closer to 1.7 miles long
The object was first identified in July 2025 by the ATLAS telescope network, which looks for objects that might hit Earth.
Earlier images taken by the Vera C Rubin Observatory in Chile this summer had unknowingly photographed the object as well, but no one realized it was there at the time.
Until now, 3I/ATLAS has been a total mystery, as early scans suggested the object was larger than anything that had passed through the solar system before, and might even be generating its own light.
This led respected Harvard astrophysicist Avi Loeb to theorize that 3I/ATLAS might have been artificially created by an extraterrestrial civilization.
However, the new findings collected in mid-August point to the object being a rare comet made of mixed chunks of CO2 and water ice, where the CO2 has kept the water ice cold, preventing it from melting into vapor as it nears the sun.
Typical comets also have visible tails or jets of gas and dust flowing behind them, but 3I/ATLAS has a more uniform cloud, which is highly unusual, and scientists are still trying to figure out if the CO2 being released is the cause.
Additionally, it’s been following a path that’s not bound to the sun, meaning it will pass through our solar system and head back into deep space, unlike Halley’s comet, which keeps coming back every 76 years.
This strange path will bring it to within 223 million miles of Earth on December 17, and it will also make even closer passes by Venus, Mars, and Jupiter this year.
The intense light coming from 3I/ATLAS was previously believed to be coming from its surface, but new scans show the light comes from a cloud around the object
3I/ATLAS is following a strange course that will take it extremely close to 3 different planets: Venus, Mars, and Jupiter
3I/ATLAS is only the third interstellar object ever detected coming from outside our solar system. Most comets originate here and orbit the sun.
However, the SPHEREx telescope found its light spectrum showed a pattern similar to certain objects in the Kuiper Belt, the region of icy bodies beyond Neptune, with water ice and organic materials.
Since this suspected comet is so much different from those typically orbiting our sun, scientists hope to learn what materials and chemicals are common in other parts of the galaxy by studying the comet’s dust, gas, and ice as it gets even closer.
They expect to find clues about how 3I/ATLAS formed and what conditions were like in its home star system, which previous studies have calculated as being on the other side of the Milky Way galaxy.
Loeb and student researcher Shokhruz Kakharov traced the path of the interstellar object to a thicker part of the Milky Way’s disk, where older stars are found.
This visiting comet, traveling nearly 150,000 miles per hour, is believed to be older than our sun, which is 4.6 billion years old.