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Three Theories About Where the Nickel Comes From

Scientists have three main ideas about what's happening:

Theory 1: Metal carbonyl molecules. These are chemicals where metal atoms bond with carbon monoxide, like nickel tetracarbonyl. They're extremely unstable—so unstable they're used in industrial processes precisely because they fall apart easily. If these molecules exist on the 3I/ATLAS, sunlight would shatter them almost immediately, releasing nickel atoms right near the surface.

Theory 2: Metals stuck to tar-like molecules. Polycyclic aromatic hydrocarbons (PAHs) are complex carbon-based molecules—think of them as cosmic tar or soot. Nickel atoms might be attached to these molecules. When ultraviolet light from the Sun hits them, the nickel breaks free.

Theory 3: Chemical reactions happening in real-time. The dust from 3I/ATLAS might contain nickel sulfide minerals (minerals where nickel and sulfur bond together). When these encounter carbon monoxide gas also streaming off the object, they could react to form nickel carbonyls right there in space, which then immediately break apart.

Each theory points to different conditions in whatever alien star system birthed this comet billions of years ago.

What Makes 3I/ATLAS a Cosmic Time Capsule

Understanding where 3I/ATLAS came from matters because these interstellar visitors are the only way we can directly study material from planetary systems around other stars.

Think about it: Even our most powerful telescopes can barely see planets orbiting nearby stars, and we certainly can't scoop up samples from them. But occasionally, the universe delivers samples to us. When an interstellar object forms around a distant star and then gets gravitationally kicked out into interstellar space, it becomes a frozen time capsule carrying chemicals from that alien solar system.

3I/ATLAS is only the third such object ever confirmed visiting our solar system:

1I/'Oumuamua (discovered 2017): A mysterious cigar-shaped or pancake-shaped object that showed no visible tail but somehow accelerated slightly as it traveled, suggesting invisible gases were pushing it. Scientists still debate what it was made of—and a few even speculated it might be artificial, though natural explanations are far more likely.

2I/Borisov (discovered 2019): A more typical-looking comet with a bright tail, similar to comets born in our solar system. However, it had way more carbon monoxide than normal comets, and it also released nickel vapor.

3I/ATLAS (discovered 2025): Initially looked like a comet but as it got closer it failed to develop the typical tail normally seen with comets. It's now spewing cyanide, nickel, carbon dioxide, carbon monoxide, and showing evidence of water ice.