The Vera C. Rubin Observatory in Chile has detected a 710-metre-wide asteroid that rotates once every 1.9 minutes, faster than previously thought possible for its size. Named 2025 MN45, it is the quickest-spinning asteroid over 500 metres across ever observed. Astronomers say its speed suggests it is a single solid rock or even metal, not a loose rubble pile.
Astronomers using the Vera C. Rubin Observatory in Chile identified the asteroid 2025 MN45 during its first nine nights of observations in late April and early May 2025. Dmitrii Vavilov at the University of Washington in Seattle and his colleagues analysed the data, spotting 76 asteroids with reliable rotational periods. Of these, 19 were super-fast rotators, spinning once every 2.2 hours or faster—the supposed limit for rubble pile asteroids held together only by gravity. The fastest among them rotates every 13 minutes or so. They also found three ultra-fast rotators with periods of 3.8 minutes, 1.92 minutes, and 1.88 minutes. The standout is 2025 MN45, measuring about 710 metres across and spinning every 1.92 minutes—faster than any known asteroid larger than 500 metres. Vavilov presented these findings at the Lunar and Planetary Science Conference in Texas on 17 March. Initially, the team did not search for rotations under 5 minutes. “We thought that was crazy that they could rotate any faster,” Vavilov said. He added, “2.2 hours is supposed to be the limit for this asteroid, and yet it’s rotating in less than 2 minutes.” Its extreme speed rules out a rubble pile structure. “Even clay would not be enough to hold this asteroid together, so it’s probably one big rock or even solid metal,” Vavilov explained. The observatory's 10-year survey of the southern sky is expected to reveal more such asteroids, highlighting their diversity. The research appears in The Astrophysical Journal Letters (DOI: 10.3847/2041-8213/ae2a30).