Envision a boulder measuring eight football fields in width, careening through the emptiness between Mars and Jupiter. Now visualize it completing a full spin every 112 seconds. According to what astronomers believed about asteroids, this object should have disintegrated millions of years ago.
But it didn’t.
This entity is known as 2025 MN45, and it’s compelling scientists to reconsider the composition of space rocks. A group utilizing the new Vera C. Rubin Observatory in Chile observed it during initial testing of the facility’s enormous camera. At 710 meters in diameter, it is now recognized as the fastest-rotating asteroid over 500 meters ever documented.
Most asteroids aren’t solid blocks of stone. They are conglomerations of rubble, loosely assembled rock and dust held together by weak gravitational forces. Spin one too rapidly, and centrifugal force will dismantle it. The theoretical threshold for large asteroids is positioned around one rotation every 2.2 hours.
2025 MN45 rotates nearly 70 times faster than that.
The Physics Don’t Align
To endure at this rotational speed, the asteroid must possess internal cohesion more akin to solid rock rather than a gravity-bound pile of debris. The team’s calculations indicate a material strength that significantly surpasses what is standard for main-belt objects.
“Evidently, this asteroid must consist of material with exceptionally high strength to remain whole while spinning at such high speeds,” Sarah Greenstreet elucidates.
Greenstreet, an astronomer at NSF NOIRLab and the principal investigator of the study, published the results in The Astrophysical Journal Letters. It represents the inaugural peer-reviewed research utilizing data from Rubin’s LSST Camera, the largest digital camera ever constructed.
The discovery was not coincidental. Within just ten hours of observations spread over seven nights in early 2025, the team discovered 19 super-fast rotators. These entities are spinning faster than the 2.2-hour fragmentation limit. Most were identified within the main asteroid belt, where such discoveries were nearly impossible prior to the launch of Rubin.
Distance rendered detection challenging. Main-belt asteroids appear significantly dimmer than near-Earth objects. Rubin’s light-gathering capability alters that dynamic.
What Rapid Rotation Reveals
Rotational rates act as fossil records. A violent impact can propel an asteroid into a whirling spin. Solar radiation pressure can gradually accelerate objects over millions of years. In either case, rapid rotation suggests an atypical internal configuration or a tumultuous history.
The identification of 19 of these fast rotators in such a brief observational period implies they may be more prevalent than previously thought. The Rubin Observatory has yet to commence its official survey.
This survey, termed the Legacy Survey of Space and Time, is set to continue for a decade. Scientists anticipate cataloging up to 5 million small bodies within our solar system. If the preliminary findings are any indication, the next ten years will unveil objects that challenge fundamental assumptions about planetary physics.
For the moment, 2025 MN45 serves as a reminder that even familiar realms can astonish us. An object of that size, spinning at such speeds, remaining whole. It defies logic.
And yet, there it remains, hurtling through the darkness.