New discovery just broke the record for fastest-spinning large asteroid
A new telescope in Chile has discovered a rapid asteroid as wide as eight football fields, making full spins in less than two minutes.
The Vera C. Rubin Observatory, built to repeatedly photograph the entire southern sky, had not yet begun its full scientific mission when it found asteroid 2025 MN45. Even so, during a brief test run, the telescope started to reveal the smallest worlds in space.
Over seven nights, Rubin's large digital camera recorded hundreds of thousands of images. In those images, astronomers identified more than 2,100 previously unknown asteroids. By watching how their brightness changed from one image to the next, researchers could measure how fast they spun and what kinds of surfaces they had.
Located in the main asteroid belt between Mars and Jupiter, 2025 MN45 is the fastest-spinning large asteroid detected so far by a long shot, said Sarah Greenstreet, a National Science Foundation NOIRLab astronomer, who presented the discovery at the 247th American Astronomical Society meeting in Phoenix this week. The previously known fast rotators complete a turn in about one hour, with some others spinning around in 30 minutes, though those asteroids had less-reliable data, she told Mashable.
"If you were standing on this ultra-fast spinning asteroid, you'd be traveling at nearly 45 mph," Greenstreet said.
Asteroids are leftover building blocks from the birth of the solar system 4.5 billion years ago. By studying how they spin, what they’re made of, and how they break and reform, scientists learn how planets — including Earth — came to be.
These findings are among the first Rubin observations published in a scientific journal, appearing in The Astrophysical Journal Letters. They already reveal a population of asteroids that had barely been sampled before. As the survey continues, discoveries like these may reshape scientists' understanding of asteroids' collisions, internal compositions, and the early solar system itself.
In particular, the initial results suggest that crashes may not be the only way asteroids reach extreme speeds, perhaps pressing astronomers to develop new explanations.
An asteroid doesn't shine on its own, but reflects sunlight. Most have lumpy, irregular shapes, so as they spin, different surfaces catch the light, causing their brightness to rise and fall in a repeating pattern. From that pattern, scientists can measure how long it takes an asteroid to rotate.
For decades, astronomers believed they understood the spin barrier. Most asteroids larger than a few hundred yards were thought to be loose piles of rock, held together by gravity. Spin them up too fast, and those bits should fling apart. That limit corresponds to a rotation time of about two hours, Greenstreet said.
But Rubin’s early data is confounding. Among the newly discovered asteroids, researchers identified 76 with reliable spin measurements. Nineteen of them rotated faster than the long-accepted limit, and three, including 2025 MN45, rotated in less than five minutes.
To remain intact, the 710-meter-wide asteroid must be made of solid rock, Greenstreet said, likely a chunk of the dense core of a larger object. A cosmic collision could have broken it free and sent it on its wild rampage.
"Determining the parent body of this fastest-rotating asteroid would be quite difficult," she told Mashable. "It's also quite possible that its parent body was catastrophically disrupted, completely breaking apart, during the collision."
Though 2025 MN45 is the reigning champion for speed right now, that may not be the case for long. Astronomers believe the telescope may find lots of these in the near future.
"With their distance away, there's a lot of the asteroid population in the main belt that we haven't been able to study before," Greenstreet said at the meeting, "but the Rubin Observatory is now just allowing us to start to get a chance to see."
