Interstellar comet 3I/ATLAS appears to be covered in erupting 'icy volcanoes,' scientists say

3I/ATLAS—the third known interstellar object to enter our solar system—continues to surprise and fascinate. A new study, titled Spectrophotometric evidence for a metal-bearing, carbonaceous, and pristine interstellar comet 3I/ATLAS, now claims that the object, having exhibited several anomalies already, is covered in icy volcano-like structures called cryovolcanoes. They also concluded that the object's interior is rich in metal, which may cause us to revisit our understanding of comet formation.

The team of scientists conducted photometric observations as 3I/ATLAS made its way towards our Sun. Before it got close to the Sun, the object was rather pristine, indicating that it had never passed so close to a star before. When it came within about 2.5 times the distance of Earth from the Sun (2.5 AU), it started exhibiting a sustained increase in brightness, which the scientists attributed to ice-based volcanic activity or cryovolcanism. 

Thereafter, the scientists compared the light reflected from the interstellar visitor's surface with that reflected off the surface of meteorite samples on Earth and found that it matched the signatures of carbonaceous chondrite (CR)—a rare type of meteorite rich in metals like nickel and iron. This led the team to the conclusion that 3I/ATLAS could also have the same composition. 

The conclusion made sense because the metal-rich composition could be a possible explanation for the alien body's significant volcanic activity. As the heat from the Sun warmed the comet's surface, water from the melting ice began corroding the metals inside, releasing energy and gases like carbon dioxide, which assist in maintaining cryovolcanism. The findings, still pending peer review, essentially put 3I/ATLAS in the same class as icy trans-Neptunian objects. Even the researchers were stunned by the implications of this. 

"We were all surprised," the lead author of the study, Josep Trigo-Rodriguez, told Live Science. "Being a comet formed in a remote planetary system, it is remarkable that the mixture of materials forming the surface of the body has a resemblance with trans-Neptunian objects, bodies formed at [a] large distance from the Sun but belonging to our planetary system."

This revelation comes shortly after controversial Harvard scientist Avi Loeb shared his thoughts on the November images of the comet taken after perihelion. In his Medium blog, he wrote that the images showed a teardrop shape of the coma pointing toward the sun. This anti-tail, he claimed, may be comprised of a swarm of objects. "If 3I/ATLAS is surrounded by a swarm of objects that do not share its non-gravitational acceleration, then these objects will tend to be closer to the Sun relative to 3I/ATLAS, because 3I/ATLAS is pushed away from the Sun relative to the objects through its non-gravitational acceleration," he wrote. 

Considering the distance of the object from the Sun at the time—around 167 million miles—Loeb asserted the objects would have been closer to the Sun by a margin of around 33,500 miles. "This separation is comparable to the sunward elongation of the teardrop glow around 3I/ATLAS," he wrote. He further claimed that a large swarm of objects would have a much larger surface area than the comet itself, even if their total mass was only a small percentage of that of 3I/ATLAS. He argued that even a swarm having just 0.001 of the mass of the comet could reflect 99% of the sunlight responsible for the observed coma glow.  

It is likely that more such claims and findings will be made in the coming months as multiple agencies continue to monitor the object as it heads out of our solar system. 3I/ATLAS will make its closest approach to Earth on December 19, 2025, when it will come within 170 million miles of the planet. 

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