Fastest-Spinning Asteroid To Date Spotted by Vera C. Rubin Observatory

2025 MN45 may not seem particularly eye-catching or remarkable, but it has piqued the interest of astronomers for a very specific reason: It is the fastest mini-planet of its size detected to date.

At 710 meters (2,297 feet), the asteroid is more than twice the length of the Eiffel Tower and rotates on its axis every 1.88 minutes.

2025 MN45 is one of thousands of asteroids recently identified by scientists at the NSF-DOE Vera C. Rubin Observatory using the Legacy Survey of Space and Time (LSST) camera, the largest digital camera ever built.

Nineteen were classified as super or ultra fast spinning. This means a spin time of less than 2.2 hours or 5 minutes, respectively. The results have now been reported in Letters from the astrophysical journal.

2025 Mn45: a record asteroid

Asteroids are small pieces of rock that have been floating around the solar system since its formation about 4.6 billion years ago. There are approximately 1.45 million of these objects known to science, the majority of which are believed to be composed of smaller rocks essentially stuck together by gravity. These are known as “rubble pile” asteroids.

This rickety structure makes them particularly vulnerable to fragmentation. The fastest piles of rubble in the main asteroid belt are thought to be able to rotate without collapsing, or one rotation every 2.2 hours.

To spin faster than 2.2 hours and avoid fragmentation, the asteroid must be structurally sound. To spin at a speed of 2 minutes or less, it must be exceptionally powerful. With a rotation time of 1.88 minutes, 2025 MN45 is the fastest known asteroid with a diameter of 500 meters or more.

“We calculate that it would need a cohesive force similar to that of solid rock,” lead author Sarah Greenstreet, NSF NOIRLab deputy astronomer and lead of the Rubin Observatory Solar System Science Collaboration’s Near-Earth and Interstellar Objects Working Group, explained in a statement.

Despite this exceptional feat, main-belt asteroid 2025 MN45 only just reached the top spot. It narrowly beat 2025 MJ71 – a near-Earth object (NEO) with a rotation time of 1.9 minutes. The other finalists had spin speeds of 3.8 minutes (2025 MK41), 13 minutes (2025 MV71), and 16 minutes (2025 MG56).

Discovery of thousands of new asteroids

The results are based on observations taken in late April and early May 2025 using the LSST camera, which detected around 2,000 never-before-seen asteroids. From these observations, astronomers at the observatory were able to calculate the shape and rotation period of asteroids by studying how their brightness fluctuates over time.

The team was able to collect reliable data on 76 asteroids with a rotation speed of less than 21.3 hours – an assemblage including one NEO, 73 main-belt asteroids, and two others on the periphery of the main asteroid belt. This contrasts with previous discoveries of rapidly rotating objects, which have mostly been classified as near-Earth objects.

Rubin Observatory: “A discovery machine”

This is just the beginning, as the Rubin Observatory is set to begin its 10-year LSST mission, a project that will consist of imaging the entire southern sky every 3 days. It is expected to capture light from up to 5 million asteroids, meteoroids and other small bodies. These findings could lead to new discoveries that improve our understanding of the history of the solar system.

“We have known for years that Rubin would act as a discovery machine for the universe,” said Aaron Roodman, deputy director of LSST and professor of particle physics and astrophysics at SLAC, in a statement. “The ability to find thousands of new asteroids in such a short time and learn so much about them is a window into what will be discovered during the 10-year investigation.”

Learn more: The Vera C. Rubin Observatory captured this Cotton Candy Nebula, here’s what it will capture next

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