Astronomers have detected an extraordinary asteroid, named 2025 MN45, in early data from the Legacy Survey of Space and Time (LSST) Camera — the largest digital camera in the world — at the NSF-DOE Vera C. Rubin Observatory.
An artist’s impression of the asteroid 2025 MN45. Image credit: NSF-DOE Vera C. Rubin Observatory / NOIRLab / SLAC / AURA / P. Marenfeld.
As asteroids orbit the Sun, they also rotate at a wide range of speeds.
These spin rates not only offer clues about the conditions of their formation billions of years ago, but also tell us about their internal composition and evolution over their lifetimes.
In particular, an asteroid spinning quickly may have been sped up by a past collision with another asteroid, suggesting that it could be a fragment of an originally larger object.
Fast rotation also requires an asteroid to have enough internal strength to not fly apart into many smaller pieces, called fragmentation.
Most asteroids are rubble piles, which means they are made of many smaller pieces of rock held together by gravity, and thus have limits based on their densities as to how fast they can spin without breaking apart.
For objects in the main asteroid belt, the fast-rotation limit to avoid being fragmented is 2.2 hours; asteroids spinning faster than this must be structurally strong to remain intact.
The faster an asteroid spins above this limit, and the larger its size, the stronger the material it must be made from.
A new paper in the Astrophysical Journal Letters provides crucial information about asteroid composition and evolution, and demonstrates how the NSF-DOE Vera C. Rubin Observatory is pushing the boundaries of what we can discover within our own Solar System.
In the study, the astronomers present 76 asteroids with reliable rotation periods.
This includes 16 super-fast rotators with rotation periods between roughly 13 minutes and 2.2 hours, and three ultra-fast rotators that complete a full spin in less than five minutes.
All 19 newly identified fast-rotators are longer than the length of an American football field (about 90 m).
The fastest-spinning main-belt asteroid identified, 2025 MN45, is 710 m in diameter and it completes a full rotation every 1.88 minutes.
This combination makes it the fastest-spinning asteroid with a diameter over 500 m that astronomers have found.
“Clearly, this asteroid must be made of material that has very high strength in order to keep it in one piece as it spins so rapidly,” said Dr. Sarah Greenstreet, an astronomer at NSF’s NOIRLab and the University of Washington.
“We calculate that it would need a cohesive strength similar to that of solid rock.”
“This is somewhat surprising since most asteroids are believed to be what we call ‘rubble pile’ asteroids, which means they are made of many, many small pieces of rock and debris that coalesced under gravity during Solar System formation or subsequent collisions.”
“Discoveries like this exceptionally fast-rotating asteroid are a direct result of the observatory’s unique capability to provide high-resolution, time-domain astronomical data, pushing the boundaries of what was previously observable,” said Regina Rameika, the DOE Associate Director for High Energy Physics.
In addition to 2025 MN45, other notable asteroid discoveries made by the team include 2025 MJ71 (1.9-minute rotation period), 2025 MK41 (3.8-minute rotation period), 2025 MV71 (13-minute rotation period), and 2025 MG56 (16-minute rotation period).
These five super- to ultra-fast rotators are all several hundred meters in diameter and join a couple of near-Earth objects as the fastest spinning sub-kilometer asteroids known.
“As this study demonstrates, even in early commissioning, Rubin is successfully allowing us to study a population of relatively small, very-rapidly-rotating main-belt asteroids that hadn’t been reachable before,” Dr. Greenstreet said.
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Sarah Greenstreet et al. 2026. Lightcurves, Rotation Periods, and Colors for Vera C. Rubin Observatory’s First Asteroid Discoveries. ApJL 996, L33; doi: 10.3847/2041-8213/ae2a30
