How precisely can astronomers measure a newly detected asteroid's size?
Core argument: Asteroid 2024 YR4 measures between 130 and 330 feet long, according to the European Space Agency's Near-Earth Object Coordination Centre, a range derived from the sunlight it reflects because its surface reflectivity is unknown.
Asteroid 2024 YR4 was identified by the Asteroid Terrestrial-impact Last Alert System four telescopes around the world that hunt near-Earth objects and are funded by NASA. Its telescope in Chile found 2024 YR4 on Dec. 27, just two days after a close approach to Earth. It’s now speeding away from the planet and getting fainter by the day. According to the European Space Agency’s Near-Earth Object Coordination Centre, it is between 130 and 330 feet long. This size range is based on the amount of sunlight it is reflecting. Without knowing exactly how reflective 2024 YR4’s surface is, only a range of sizes can be given. A more accurate estimate could be made using radar, but that won’t be possible until the asteroid makes another close, but perfectly safe, pass by Earth on Dec. 17, 2028. A 130-foot asteroid is comparable to the Tunguska impactor, a meteor that exploded over a remote patch of Siberia in 1908 and decimated an 800-square-mile forest.



