YR4 is about 60 meters wide: picture a 15-story building turned on its side and moving around the Sun. The asteroid associated with the dinosaurs’ extinction was roughly 10 kilometers across—well over 150 times wider.
That size range is large enough for NASA to expect an atmospheric airburst if such an object entered Earth’s atmosphere, and it explains why YR4’s earlier impact probability received serious attention. It is also small enough that Webb set a record by observing it as the telescope’s smallest asteroid target at the time.
During the close 2032 passage, that building-size rock will still appear as little more than a point of light. The fun lies in how much astronomers can learn from that point—its heat, spin, brightness, and path through the Earth–Moon neighborhood.