We saw a huge asteroid spinning impossibly fast

The Vera C. Rubin Observatory in Chile recorded the fastest rotating large asteroid ever seen. Although measuring more than half a kilometer in diameter, this asteroid rotates approximately once every 1.9 minutes – a speed previously thought impossible.

Dmitry Vavilov at the University of Washington in Seattle and his colleagues found this asteroid, along with several other surprisingly fast rotators, in data from Rubin’s first nine nights of observations in late April and early May 2025. Vavilov introduced results at the Lunar and Planetary Science Conference in Texas on March 17.

In this observation period, scientists identified 76 asteroids for which they could reliably calculate rotation periods, 19 of which were so-called super-rapid rotators, which rotate once every 2.2 hours or faster. This number is a limit to how fast a “debris pile” asteroid made up of many smaller rocks loosely held together by gravity can spin without breaking apart.

The vast majority of asteroids are considered debris piles, so researchers didn’t expect to find many rotating faster than once every 2.2 hours. The fastest of the superfast rotators spins once every 13 minutes. In their first set of analyses, the researchers didn’t even look for anything with a rotation period of less than about 5 minutes, Vavilov said during his presentation. “We thought it was crazy that they could spin faster,” he said.

When they went back and looked for even faster rotators, they found three spinning so fast that they are considered ultrafast rotators with periods of about 3.8 minutes, 1.92 minutes, and 1.88 minutes. The fastest, called 2025 MN45, is about 710 meters in diameter and spins faster than any asteroid larger than 500 meters in diameter that has ever been seen.

Its staggering speed means this asteroid can’t be a pile of rubble. It must be made of much stronger steel than most space stones. “2.2 hours should be the limit for this asteroid, and yet it rotates in less than 2 minutes,” Vavilov said. “Even clay wouldn’t be enough to hold this asteroid together, so it’s probably one big rock or even solid metal.”

The Vera C. Rubin Observatory is expected to spot many more spinning asteroids during its planned 10-year survey of the southern sky, allowing astronomers to explore the surprising diversity of these strange boulders in space.

topics: