Artist’s rendering of asteroid 2025 MN45
NSF–DOE Vera C. Rubin Observatory/NOIRLab/SLAC/AURA/P. Marenfeld
The Vera C. Rubin Observatory in Chile has discovered the fastest rotating large asteroid ever seen. Despite measuring more than half a kilometer across, this asteroid spins about once every 1.9 minutes – a speed once thought to be impossible.
Dmitrii Vavilov of the University of Washington in Seattle and his colleagues found this asteroid, along with several other surprisingly fast rotators, in the data from Rubin’s first nine nights of observations in late April and early May 2025. Vavilov presented the results at the Lunar and Planetary Science Conference in Texas on March 17.
During that observation period, the researchers identified 76 asteroids for which they could reliably calculate rotation periods, with 19 of these being so-called superfast rotators, spinning once every 2.2 hours or faster. That number is the limit to how fast a “ruble pile” asteroid, which is made up of many smaller rocks loosely held together by gravity, can spin without falling apart.
The vast majority of asteroids are thought to be clumps of rock, so scientists didn’t expect to find many that rotated faster than once every 2.2 hours. The fastest of the superfast rotators spins once every 13 minutes or so. In their first set of analyses, the researchers didn’t even look for anything with a spin period of less than about 5 minutes, Vavilov said during the presentation. “We thought it was crazy that they could rotate faster,” he said.
When they went back and looked for even faster rotators, they found three that spun so fast that they are considered ultrafast rotators, with periods of about 3.8 minutes, 1.92 minutes, and 1.88 minutes, respectively. The fastest, called 2025 MN45, has a diameter of about 710 meters and spins faster than any asteroid more than 500 meters in diameter ever seen before.
Its astonishing speed means that this asteroid cannot possibly be a pile of rocks. It must be made of much stronger material than most space rocks. “2.2 hours is supposed to be the limit for this asteroid, and yet it rotates in less than 2 minutes,” Vavilov said. “Even clay would not be enough to hold this asteroid together, so it is probably a large rock or even solid metal.”
The Vera C. Rubin Observatory is expected to discover many more rotating asteroids during its planned 10-year survey of the southern sky, allowing astronomers to explore the surprising diversity of these strange boulders in space.
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