The James Webb Space Telescope is famous for galaxies so distant that their light began traveling before Earth existed. In 2025, it pulled off a very different trick: studying a nearby asteroid only about 60 meters wide.
Webb looked at sunlight bouncing off YR4 and at heat radiating from it. Combining those views helped researchers estimate a diameter of roughly 174 to 220 feet (53 to 67 meters)—about the height of a 15-story building laid on its side.
Webb did not photograph a crisp, cratered boulder; YR4 remained a faint dot. The cleverness lies in learning from the light that dot gives off. Researchers even found hints of surface rocks around fist-size or larger. For a telescope built to study the grandest structures in the universe, sizing up a tiny 2032 visitor is delightfully precise detective work.