Look up at the night sky, and every star, planet, and comet you see is a local. They all belong to our cosmic neighborhood, the solar system. But every once in a while, a stranger passes through—a tourist from an entirely different star system. In the summer of 2025, astronomers spotted just such a visitor: Comet 3I/ATLAS.

This isn’t just another comet; it’s a rare and exciting interstellar object, only the third ever confirmed. It’s a frozen, rocky messenger from a place we may never know, on a one-way trip through our celestial backyard. Let’s dive into everything you need to know about this incredible discovery.