The Rubin Observatory Unveils the Swiftest Spinning Asteroid Ever
In a groundbreaking discovery, the Vera C. Rubin Observatory has unveiled the fastest-spinning asteroid ever observed, measuring over 500 meters in size. Named 2025 MN45, this 710-meter-long asteroid resides in the main asteroid belt between Jupiter and Mars, completing a rotation in a mere 1.88 minutes. This remarkable find, alongside 18 other fast-rotating asteroids, marks the initial scientific output from the Rubin Observatory's Legacy Survey of Space and Time (LSST). The findings were published on January 7, 2026, in the Astrophysical Journal Letters (https://iopscience.iop.org/article/10.3847/2041-8213/ae2a30).
The data, captured in April and May 2025 during the telescope's instrument commissioning, offered a sneak peek into the Rubin Observatory's capabilities in June 2025 (https://rubinobservatory.org/news/rubin-first-look). However, the full 10-year observing campaign commences in 2026.
Luca Rizzi, an NSF program director for research infrastructure, emphasizes the observatory's potential: "NSF–DOE Rubin Observatory will uncover phenomena that no one even knew to look for. When the Legacy Survey of Space and Time begins, this colossal spinning asteroid will be just the tip of the iceberg, with an avalanche of new information about our Universe captured nightly."
Asteroids in the main belt typically spin at a leisurely pace, below 2.2 minutes per rotation, a phenomenon known as the spin barrier. Spinning faster than this often leads to asteroids breaking apart or forming binary systems. The spin barrier is influenced by factors like the ratio of icy to rocky material, size, and whether the asteroid is a solid chunk or a collection of smaller pieces.
The study's lead author, Sarah Greenstreet, explains the extraordinary nature of 2025 MN45: "Clearly, this asteroid must be composed of material with exceptionally high strength to remain intact during its rapid rotation. Our calculations indicate that it would require a cohesive strength akin to that of solid rock."
Among the other asteroids discovered, 2025 MJ71 stands out as the second-fastest spinner, rotating at nearly 1.9 minutes per rotation. Of the 19 fast rotators described in the paper, only one resides outside the main asteroid belt. Prior to the Rubin Observatory, most known fast rotators were near-Earth objects. The observatory's unique capabilities enable detailed observations at greater distances, promising a treasure trove of new data about the asteroid belt and beyond.
Beyond its impressive digital camera, the Rubin Observatory's key strength lies in its repeated surveys of the night sky, capturing 'transients'—events that change from night to night, including asteroids, potential new planets, supernovae, and variable stars. Over ten years, the LSST will create a detailed map of the Milky Way and aid astrophysicists in understanding dark matter by cataloging distant galaxy sizes.
