Data collected by the Vera C. Rubin Observatory months before the main survey began has already transformed our understanding of asteroids.
In the main asteroid belt between the orbits of Mars and Jupiter, telescopes have discovered a huge asteroid that is spinning incredibly fast. Its name is 2025 MN45it has a diameter of 710 meters (2,330 feet) and a rotation period of only 1.88 minutes.
This is well above the 2.2-hour rotation barrier beyond which asteroids larger than 150 meters should scatter into pebbles as centrifugal forces supersede the asteroid’s presumed structural integrity.
In addition, the observations also found that 18 other asteroids were rotating at “impossibly” high speeds. These results suggest that asteroids may be much more powerful than scientists previously thought.
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“The unexpected prevalence of asteroids the size of several football fields (greater than 500 meters in diameter) that complete complete rotations in less than two minutes requires us to refine our understanding of asteroid rotation formation and evolution,” wrote a team led by astronomer Sarah Greenstreet of the National Science Foundation’s National Optical Infrared Astronomy Research Laboratory.
The solar system has more asteroids, objects smaller than mature planets, rather than comets, than any other planet. These objects often preserve a pristine record of the composition of the solar system from the time of its formation.
However, they are not easy to learn. They are small, dark, far away, and often moving. This means that it is difficult to obtain a detailed catalog of its characteristics, such as size, shape and rotation.
One of Rubin’s missions is to conduct a more detailed inventory of asteroids than has been achieved so far, greatly expanding our knowledge of these ancient and mysterious objects.
The telescope was put into operation during pre-survey observations. For decades, astronomers thought they had a good idea of how fast an asteroid could safely spin without breaking apart. That’s because most asteroids are thought to be “rubble piles” – pebbles, dust and boulders loosely held together by gravity.
If one of these piles of rubble spins too fast, the loose bonds are overcome by centrifugal force. Imagine a graviton, and as it spins, the person riding on it is thrown against a wall.
If you put a single, large, cohesive mass at the center of a graviton, that mass will stay the same. If the mass is made up of smaller components that are only weakly held together, it will break apart.
For large main-belt asteroids, this splitting point is set to a rotation period of about 2.2 hours – a hard limit proposed by theory in the 1990s and confirmed in 2000 by observations of the main belt, which showed that few objects larger than 150 meters have rotation periods shorter than this threshold.
This means that most asteroids are indeed rubble piles, and while there may be more solid objects out there, they are thought to be few and far between.
Rubin’s observation campaign took place over nine nights between April 21 and May 5, 2025, during which time information on approximately 340,000 asteroids was collected. Greenstreet and her colleagues used a large amount of data to measure the rotation of 76 asteroids, 75 of which were in the main belt and one lingering in near-Earth space.
Among them, 19 asteroids have rotation periods shorter than the rotation barriers: 16 are ultrafast spinners, with periods between 2.2 hours and 13 minutes, and the remaining 3 are ultrafast spinners, with periods less than 5 minutes.
This was a big surprise: Most of the rapidly rotating objects discovered so far are near-Earth asteroids, which are closer to the sun. Main-belt asteroids are thought to be much slower and more stable. Only one new rapidly rotating object is a near-Earth object.
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2025 bright moon45 It’s obviously the record-breaking asteroid, but there are others that shouldn’t be ignored. The fact that such a large proportion of the sample challenges the spin barrier means that we may be significantly underestimating the number of main-belt asteroids with high density and structural integrity.
“Obviously, this asteroid must be made of a material with very high strength in order to maintain its integrity as it spins rapidly,” Greenstreet said. “We calculated that it would need similar cohesive strength to solid rock.”
This is very exciting. Solid chunks of rock like this may be survivors of unusually violent collisions during the chaos of the early solar system, retaining an internal structure that most asteroids lost long ago.
This bodes well for future Rubin observations, as well as missions like Lucy, NASA’s current spacecraft that explores asteroids at close range.
“Due to the possible unusual composition, internal structure, and/or formation history, a larger sample of these rapidly rotating asteroids is likely to change our understanding of the physical structure and collision history of asteroids and, to a greater extent, our understanding of the formation and evolution of the solar system,” the researchers wrote.
The research results were published in Astrophysical Journal Communications.
