[Astrophysics Colloquium] It came from outer space: 3I/ATLAS and the interstellar object population

The discovery of 3I/ATLAS, the third interstellar object to be detected, in July triggered a frenzy of observational and theoretical effort. Our modelling shows this is likely the oldest object ever seen close up, a relic of the processes governing planet formation more than eight billion years ago. In this talk, I'll review what these enigmatic objects can tell us, how we're using what we know about the galaxy to predict their properties, and what the discovery of another 100 interstellar objects by Rubin might tell us.