Interstellar comet 3I/ATLAS carries chemistry older than the Sun

After 3I/ATLAS passed the Sun in late 2025, Webb’s NIRSpec instrument measured gases released from its warmed ice. ESA’s report says the comet contained roughly thirty times more deuterium than Solar System comets and very little carbon-13 relative to carbon-12—chemical ratios that preserve information about where and when its material formed.

Researchers estimate the third confirmed interstellar comet may have formed ten to twelve billion years ago in a cold, radiation-rich environment, long before the Sun existed. The result turns a brief visitor into a physical sample of another planetary system’s history and gives scientists a direct comparison for the chemistry that preceded life in our own system.

Why it matters

Interstellar objects let scientists test whether the ingredients and environments found in our Solar System are common across the galaxy rather than relying only on distant light.

What the source establishes

3I/ATLAS is a confirmed natural interstellar comet. Its unusual chemistry records a different formation environment; it is not evidence of artificial construction.