The most recent interstellar visitor was crisscrossing our galaxy for some 10 to 12 billion years before it came near the Sun.

Comet 3I/ATLAS was discovered on July 1, 2025. The Gemini South telescope in Chile captured this image of the comet on August 27, 2025.

International Gemini Observatory / NOIRLab / NSF / AURA et. al

The visitors we know of from far beyond the solar system are rare. We’ve only found three so far: First, there was the oddly non-cometary 1I/’Oumuamua, discovered in 2017, followed closely by the more ordinary 2I/Borisov. Then, in the last year, astronomers caught wind of Comet 3I/ATLAS. With only a few months to observe the comet before it retreated beyond view, they raced to collect data on this little world both before and after its encounter with our baking-hot Sun.

Now, those data are telling a story: This comet came from far away — not only from us, but also from its parent star.…