YR4 entered the catalog on December 27, 2024, thanks to ATLAS, the Asteroid Terrestrial-impact Last Alert System. A survey telescope at Río Hurtado, Chile, caught the object two days after its closest pass that Christmas, as it moved out of the daytime sky and began fading.
There was no heroic astronaut chase—just a telescope repeatedly photographing the sky, software noticing a moving point, and astronomers reporting it for confirmation. That quiet routine is the front door of planetary defense.
ATLAS was built to notice objects that change position between exposures. Most discoveries become ordinary catalog entries. YR4 became something more: a building-size object with a 2032 route through the Earth–Moon neighborhood. Spot first, share quickly, then turn a handful of moving pixels into a celestial itinerary.