A Half-Mile-Wide Asteroid Is Spinning So Fast It Should Have Shattered Long Ago
Finn's Take· TL;DR- 710-meter asteroid 2025 MN45 spins every 1.88 minutes, far exceeding the theoretical breaking point for objects its size.
- Discovery suggests it's solid rock or consolidated material, not a loose rubble pile, likely ejected from a larger body billions of years ago.
- Finding hints many more ultra-fast-spinning asteroids exist; full LSST survey could revolutionize understanding of asteroid composition and structure.
A Record-Breaking Spin That Defies the Rules
Deep in the main asteroid belt between Mars and Jupiter sits a space rock named 2025 MN45 — 710 meters across, spinning once every 1.88 minutes. That's far past the 2.2-hour spin barrier, beyond which asteroids larger than 150 meters should fly apart into pebbles as centrifugal forces overwhelm their structural integrity. And yet, somehow, it holds together. Astronomers announced the discovery in January 2026, and the scientific community is still grappling with what it means.
The record-breaking space rock is larger than most skyscrapers on Earth and completes a rotation in about 113 seconds — making it the fastest-spinning known asteroid over 500 meters in diameter. This discovery, along with that of 18 other fast rotators, represents the first published science results from the Rubin Observatory's Legacy Survey of Space and Time (LSST), released in the Astrophysical Journal Letters.
What Makes This So Unusual
Most asteroids are rubble piles — 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. The theoretical expectation is that a 710-meter rubble pile spinning with a period of 1.88 minutes should fragment, its constituent pieces flying off as centrifugal forces overcome gravity. Yet 2025 MN45 clearly does not. The researchers conclude it must be composed of material with exceptional cohesive strength — either solid rock or consolidated clay — making it fundamentally different from the expected composition of large main-belt asteroids.
Scientists believe it's likely a collisional fragment of a much larger parent body that, early in the solar system's history, was heated enough that its internal material melted and differentiated. A primordial collision then blasted 2025 MN45 from the dense core of that parent body and sent it whirling into space. That origin story would explain both its unusual solidity and its extreme spin — a relic of ancient violence preserved for billions of years.
How the Discovery Was Made
The team accumulated 517 observations across 12 days. The same rotation period appeared when the data were separated by night and color filter, and two independent techniques recovered it — important checks, because an extreme period can otherwise be an artifact created by observing cadence. The resulting data produced a light curve showing the asteroid's fluctuating brightness as it spins, which can help scientists determine rotation period, size, shape, and surface properties.
Beyond 2025 MN45, the team found 16 additional "super-fast rotators" spinning at rates between 13 minutes and 2.2 hours per revolution — plus two other "ultra-fast rotators" completing a full revolution in less than five minutes. Researchers now think there could potentially be "lots" of these speedy spinners lurking in the belt between Mars and Jupiter — objects that have so far evaded detection simply because no telescope was powerful enough or fast enough to catch them.
A Preview of What's Coming
The full 10-year Legacy Survey of Space and Time will create a wide-view, high-definition, time-lapse record of the universe, relying on images captured by the 3.2-billion-pixel LSST Camera — the largest digital camera in the world. This discovery suggests that current models of main-belt asteroid composition may be incomplete, and that some large asteroids retain or have reformed into coherent structures far stronger than rubble-pile models predict.
What's most striking is that this find came from pre-survey data — a warm-up act before the main event even began. As one researcher put it, the ability to find thousands of new asteroids in such a short period and learn so much about them is a window into what will be uncovered during the full 10-year survey. If a single anomaly-shattering discovery emerged from just a handful of early nights, the years ahead promise to fundamentally reshape our understanding of the solar system's ancient architecture.