Free Astronomy Magazine July-August 2025

26 ASTRO PUBLISHING needs to be used to deflect the as- teroid if it is deemed a threat.” Despite being a scenario widely pon- dered by astronomers and Holly- wood writers for decades, further observations have since determined YR 4 will not impact the Earth in 2032 as originally predicted. However, there is a ~2% chance it could hit the Moon instead. “At about 50-60 meters in diameter (similar to the width of a football field), it’s one of the largest objects in recent history that could hit the Moon,” added Bolin. “If it does, it would give scientists a rare chance to study how the size of an asteroid relates to the size of the crater it cre- ates—something we haven’t been able to measure directly before.” Asteroids that are 100 meters or larger are often what astronomers call “rubble piles,” made up of frag- ments from a larger parent asteroid that broke apart in a collision. The JULY-AUGUST 2025 A stronomers using W. M. Keck Observatory on Maunakea, Hawai ‘ i Island have deter- mined the physical properties and potential origin of 2024 YR 4 , the Earth-crossing asteroid first discov- ered by scientists in December 2024. The study reveals YR 4 is a solid, stony type that likely originated from an asteroid family in the central Main Belt between Mars and Jupiter, a re- gion not previously known to pro- duce Earth-crossing asteroids. “YR 4 spins once every 20 minutes, rotates in a retrograde direction, has a flattened, irregular shape, and is the density of solid rock,” said Bryce Bolin, research scientist with Eureka Scientific and lead author of the study. “The shape of the asteroid provides us with clues as to how it formed, and what its structural in- tegrity is. Knowing these properties is crucial for determining how much effort or what kind of technique The surprising origins of asteroid 2024 YR 4 by Keck Observatory