2025 MN45
Fastest rotating large asteroid known as of 2026.
2025 MN45 is a main-belt asteroid roughly 0.71 kilometers (0.44 miles) across, discovered on 2 May 2025 by the Vera C. Rubin Observatory. As of 2026, it holds the record for the fastest rotation among any asteroid larger than 0.5 kilometers (0.31 miles), spinning once every 1.88 minutes. This extreme spin rate suggests the object is not a loose rubble pile but is composed of strong material, such as solid rock, that can withstand the centrifugal forces trying to tear it apart.
**Discovery** The asteroid was spotted during the commissioning of the Rubin Observatory’s 8.4-meter Simonyi Survey Telescope and its main camera, the LSSTCam. It was one of roughly 1,900 asteroids found in the observatory’s “First Look” program, which repeatedly imaged the Virgo Cluster from April to May 2025. The discovery was announced by the Rubin team in June 2025, with data submitted to the Minor Planet Center. Further analysis of those observations revealed the rapid rotation, announced on 7 January 2026 by a team led by Sarah Greenstreet. Pre-discovery images from the Pan-STARRS survey, taken in 2019, 2021, and 2023, also show 2025 MN45.
**Orbit** 2025 MN45 orbits the Sun at an average distance of 2.49 astronomical units (AU), placing it in the main asteroid belt between Mars and Jupiter. It completes one orbit every 3.81 years. The orbit is nearly circular, with an eccentricity of 0.02 and an inclination of 9.9° relative to the ecliptic.
**Physical properties** The asteroid’s diameter of 710 meters (0.44 miles) was estimated from its absolute magnitude of 18.7 and an assumed albedo of 0.15. Color measurements from the Rubin observations show g–r indices of 0.42–0.43 and r–i indices of 0.13–0.14, which align more closely with C-type (carbonaceous) asteroids than S-type (stony) ones. Its brightness varies by 0.4 magnitudes, indicating an elongated shape with an axial ratio of at least 1.3, corresponding to approximate dimensions of 0.87 × 0.66 kilometers.
**Rotation** The periodic brightness changes reveal a rotation period of 1.88 minutes, making 2025 MN45 the fastest-spinning asteroid larger than 500 meters (1,600 feet) known as of 2026. Most main-belt asteroids larger than 150 meters (490 feet) are expected to rotate no faster than about 2.2 hours—a limit called the spin barrier—because faster rotation would break apart a loosely bound rubble pile.
- Diameter
- 0.71 km (0.44 mi)
- Discovery date
- 2 May 2025
- Discovery site
- Vera C. Rubin Observatory
- Rotation period
- 1.88 minutes
- Semi major axis
- 2.49 AU
- Orbital period
- 3.81 years
- Orbital eccentricity
- 0.02
- Orbital inclination
- 9.9°
Lore & Background
2025 MN45 was discovered during the commissioning of the Vera C. Rubin Observatory's Simonyi Survey Telescope as part of its 'First Look' program, which imaged the Virgo Cluster frequently from April to May 2025. The discovery was announced in June 2025, and its rapid rotation was announced on 7 January 2026 by a team led by Sarah Greenstreet. Earlier observations from Pan-STARRS in 2019, 2021, and 2023 also detected the asteroid.
The asteroid orbits the Sun at an average distance of 2.49 AU, with a nearly circular orbit (eccentricity 0.02) and an inclination of 9.9°. Its diameter of 710 m was estimated from an absolute magnitude of 18.7 and an assumed albedo of 0.15. Color indices suggest it matches C-type asteroids more closely than S-type. Brightness fluctuations of 0.4 magnitudes indicate an elongated shape with axial elongation at least 1.3, corresponding to dimensions of 0.87 × 0.66 km.
Its rotation period of 1.88 minutes far exceeds the 2.2-hour spin barrier typical for main-belt asteroids larger than 150 m. This implies 2025 MN45 is not a rubble pile but a solid, cohesive body with internal strength comparable to solid rock (about 9 MPa). Two other ultrafast rotators with periods under 5 minutes were discovered in the same study, suggesting such objects may be common and possibly originate from collisional destruction of a larger parent body's dense core.
Reader's Guide
2025 MN45 is significant because it challenges the conventional understanding of asteroid structure and rotation limits. Most main-belt asteroids larger than 150 m are expected to rotate no faster than about 2.2 hours, as faster spins would tear apart loosely bound rubble piles. However, 2025 MN45 rotates once every 1.88 minutes—over 70 times faster than this barrier—indicating it is made of strong, cohesive material like solid rock. This makes it the fastest rotating asteroid with a diameter larger than 0.5 km as of 2026. Its discovery by the Vera C. Rubin Observatory during its 'First Look' program highlights the observatory's capability to find unusual objects. The fact that two other ultrafast rotators were found in the same study suggests such objects may be more prevalent than previously thought, possibly originating from the dense cores of disrupted parent bodies. This has implications for understanding asteroid internal structures and the processes that shape them.
Did You Know?
- 2025 MN45 completes one rotation every 1.88 minutes, the fastest known for any asteroid larger than 0.5 km as of 2026.
- It was discovered by the Vera C. Rubin Observatory on 2 May 2025 during the commissioning of its LSSTCam.
- Its rapid rotation implies it is made of solid rock with a cohesive strength of about 9 MPa, not a rubble pile.
- The asteroid was also detected in earlier Pan-STARRS observations from 2019, 2021, and 2023.
Frequently Asked Questions
What is 2025 MN45?
2025 MN45 is a main-belt asteroid roughly 0.71 kilometers (0.44 miles) in diameter, first detected on 2 May 2025 by the Vera C. Rubin Observatory. It circles the Sun at a semi-major axis of about 2.49 AU, completing one orbit every 3.81 years.
Why is 2025 MN45's spin rate so remarkable?
At just 1.88 minutes per full rotation, it holds the record for the fastest-spinning asteroid larger than 0.5 km, a distinction it still held as of 2026. That speed is so extreme that a loose collection of boulders would simply be flung apart, so the body must be held together by genuinely strong material.
Who discovered 2025 MN45 and when?
The Vera C. Rubin Observatory identified the asteroid on 2 May 2025 during the commissioning phase of its 8.4-meter Simonyi Survey Telescope. The detection was part of the facility's early survey operations as the instrument was being calibrated for full science.
What does 2025 MN45's fast rotation tell us about its composition?
Spinning that quickly produces enormous centrifugal stress that a rubble-pile structure could never endure. The fact that the asteroid remains intact strongly implies it is built from cohesive, high-strength material—most likely solid rock rather than loosely bound fragments.
Where does 2025 MN45 orbit in the solar system?
It travels in the main asteroid belt at a semi-major axis of roughly 2.49 AU, placing it between the orbits of Mars and Jupiter. One complete revolution around the Sun takes about 3.81 Earth years.
More in Notable Asteroids 1-24
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