2025 MN45
is a rapidly rotating main-belt asteroid in diameter, discovered by the Vera C. Rubin Observatory on 2 May 2025. It has the shortest known rotation period of any asteroid with a diameter larger than , completing one rotation approximately every 1.88 minutes. The extreme spin rate of indicates that it is not a rubble pile, but is instead made of a strong material like solid rock which prevents centrifugal forces from breaking it apart.
Discovery
was discovered by the Vera C. Rubin Observatory's Simonyi Survey Telescope on 2 May 2025, during the commissioning of its main telescope camera. It is one of the ~1,900 asteroids discovered by the observatory during its "First Look" program, which detected them via frequent imaging of the Virgo Cluster from April to May 2025. The discovery of these asteroids including was announced by Vera C. Rubin Observatory team in June 2025, with the observation data submitted to the Minor Planet Center. Further analysis of Vera C. Rubin Observatory's "First Look" observations revealed that had a rapid rotation, which was announced on 7 January 2026 by a team of astronomers led by Sarah Greenstreet. has been detected by the Pan-STARRS survey in earlier observations from 2019, 2021, and 2023.Orbit
orbits the Sun at an average distance or semi-major axis of 2.49 astronomical units, which places it in the main asteroid belt between Mars and Jupiter. It completes one orbit around the Sun every 3.81 years. The asteroid follows a nearly circular orbit with a low orbital eccentricity of 0.02 and an inclination of 9.9° with respect to the ecliptic.Physical properties
has an estimated diameter of, which was determined from its absolute magnitude of 18.7 and an assumed geometric albedo of 0.15. Analysis of Vera C. Rubin Observatory's April–May 2025 observations has shown that has color indices of g–''r 0.42–0.43 and r''–i 0.13–0.14, which appear to match more closely with C-type asteroids than S-type asteroids. The observations also show that 's brightness fluctuates with an amplitude of 0.4 magnitudes, indicating that it has an elongated shape with an axial elongation of at least 1.3.Rotation
The brightness of periodically changes due to its rotation. Analysis of Vera C. Rubin Observatory's April–May 2025 observations found that rotates every 1.88 minutes, making it the fastest rotating asteroid with a diameter larger than . Main-belt asteroids with diameters larger than are generally expected to rotate slower than about 2.2 hours, as centrifugal forces would cause a loosely bound object to break apart. The fact that rotates far faster than the 2.2-hour spin barrier implies that it is not a rubble pile like most asteroids, but is instead made of a very strong material with substantial internal cohesion. The cohesive strength required to keep intact against centrifugal forces is roughly 9 megapascals, comparable to that of solid rock.In addition to, two other "ultrafast"-rotating asteroids with diameters larger than and rotation periods shorter than 5 minutes were discovered in the same Vera C. Rubin Observatory study, suggesting that they might be prevalent. These ultrafast rotators may have originated as fragments from the collisional destruction of a larger parent body's dense core.