Have you ever looked inside a freezer and found ice hiding under the top layer? It looks simple at first. But inside, there can be a surprise.

That is a little like comet 3I/ATLAS. Its name sounds cold and strange, and that fits. The “3I” means it is the third known object ever seen coming from outside our solar system. It was first reported on July 1, 2025, by the ATLAS survey telescope in Chile, and it was never a danger to Earth. (science.nasa.gov)

Later, after the comet swung around the Sun in late October 2025, NASA’s James Webb Space Telescope looked at it again in December 2025 as it moved back out of our solar system. So imagine this: the outside of the comet had already been heated. Then, little by little, deeper ice started to wake up. (science.nasa.gov)

And then came the exciting part. Webb directly found methane gas on 3I/ATLAS. This was the first direct methane detection on an interstellar visitor. Scientists also found that the comet has a lot of carbon dioxide compared with water. NASA says the methane may have stayed hidden under the comet’s top layer until heat from the Sun reached deeper inside. (science.nasa.gov)

Why does that matter? Because this comet does not look like most comets from our own solar system. Its chemistry seems different. It may have formed in a very different place around another star. (science.nasa.gov)

So when you hear “comet,” maybe don’t think only of a bright tail in the sky. Think of a traveler carrying a small secret from another star—and sharing it only when it gets warm enough to speak. (science.nasa.gov)