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By Samuel A. Lopez, USA Herald – October 24, 2025

USA HERALD - When the interstellar object now known as 3I/ATLAS was discovered this summer by NASA’s ATLAS telescope in Chile, astronomers expected another ordinary cosmic traveler, much like ʻOumuamua or Borisov. They were wrong. The strange visitor, now hurtling through our solar system on a hyperbolic escape path, is rewriting what scientists thought they knew about comets—and possibly about how planets form across the galaxy.

For months, headlines have repeated the same talking points: “third interstellar object,” “no danger to Earth,”“passing through the solar system.” But the real story, one buried beneath the routine coverage, is that 3I/ATLAS behaves in ways that defy the norms of cometary science. Behind the scenes, telescopes from Earth orbit to Mars are watching it like detectives at a crime scene—because this one doesn’t match any known profile.

A Chemical Mystery Written in Gas and Ice

The James Webb Space Telescope has revealed something extraordinary: 3I/ATLAS’s vapor cloud, or coma, is dominated by carbon dioxide rather than water. In most comets, water ice is the main volatile, sublimating into gas as the comet nears the Sun. But for 3I/ATLAS, the CO₂-to-water ratio is about eight to one—an extreme outlier never observed in our solar system.

That imbalance suggests it may have formed in a completely different environment—perhaps in the icy outskirts of another star system, or closer to a CO₂ “frost line” where water was scarce. Researchers from Caltech’s SPHEREx mission confirmed the findings, noting that its spectral signature implies an alien chemistry not represented in our local comet catalogues.

“This is the first truly carbon dioxide–dominated comet we’ve ever observed,” one researcher remarked. “It challenges our assumptions about where and how icy bodies form in planetary systems.”

Unusual Light, Unusual Dust

Even its light behaves strangely. Polarimetric readings—measurements of how light scatters off dust—show a pattern unseen in any other known comet. The data suggest that 3I/ATLAS’s dust particles are structured differently, possibly denser or metallic in composition. This polarisation signature could mean that interstellar comets aren’t just distant cousins of our own, but a completely different class of celestial body.

As it moves toward its October 30 perihelion, 3I/ATLAS’s coma continues to brighten and shift in hue, now emitting a faint green glow from excited carbon molecules. Some astronomers have called it “a living lab for cosmic chemistry,” while others caution that its unpredictable activity could make it fragment or break apart before the year is over.