The vast, silent expanse of our solar system has just played host to a visitor from the deepest reaches of the galaxy, and it is proving to be unlike anything astronomers have ever witnessed. While most of the cosmic debris we encounter is 'local' — leftovers from the birth of our own sun — every so often, an interloper from another star system comes screaming through our neighbourhood. Travelling at a staggering hyperbolic excess velocity of 58 kilometres per second — far faster than its predecessors 1I/ʻOumuamua and 2I/Borisov — this visitor arrived with an energy that has forced a rethink of our cosmic surroundings.
The newest and maybe most important of these guests is 3I/ATLAS. The ATLAS system in Chile found this interstellar comet in July 2025. Since then, every major telescope on Earth has been poking and prodding it. Even now, weeks after it came closest to Earth on Dec. 19, 2025 and sailed by us at a safe distance of 270 million kilometers, scientists are still trying to make sense of the data this fast-moving object left behind.
