Even before its primary observational phase has commenced, the Vera C. Rubin Observatory has begun to fundamentally alter our perception of celestial bodies, based on data gathered months in advance.
Within the Main Belt, situated between the planetary orbits of Mars and Jupiter, this advanced telescope has identified a substantial asteroid rotating at an astonishing velocity. Designated 2025 MN45, this object spans 710 meters (2,330 feet) in diameter and completes a full revolution in a mere 1.88 minutes.
This rotational speed significantly exceeds the previously established 2.2-hour threshold, beyond which asteroids larger than 150 meters were theorized to disintegrate into smaller fragments due to centrifugal forces overpowering their presumed structural integrity.
Furthermore, these initial observations have cataloged 18 additional asteroids exhibiting rotational rates considered impossibly high. These discoveries strongly indicate that asteroids may possess considerably greater inherent strength than previously posited by the scientific community.
“The unanticipated prevalence of asteroids, comparable in size to several football fields (with diameters exceeding 500 meters), completing a rotational cycle in less than two minutes necessitates a revision of our comprehension regarding the formation and developmental trajectory of asteroid rotations,” asserts a research contingent spearheaded by astronomer Sarah Greenstreet from the US National Science Foundation’s National Optical-Infrared Astronomy Research Laboratory.
The Solar System harbors a greater abundance of minor planets – celestial fragments smaller than terrestrial planets and distinct from comets – than any other category of object. These bodies often serve as unaltered archives, preserving the primordial composition of the Solar System from its nascent stages.
However, their study presents considerable challenges. Their diminutive size, low reflectivity, and considerable distances, coupled with their dynamic movement, render the acquisition of detailed characterization data, including dimensions, form, and rotational patterns, a complex undertaking.
A significant objective of the Rubin Observatory’s mission is to compile an unprecedentedly thorough inventory of asteroids, thereby vastly augmenting our knowledge of these ancient and enigmatic entities.
The telescope has demonstrated exceptional performance from its earliest observational period. For decades, astronomical understanding held that asteroids possessed a well-defined limit for safe rotational velocity before structural failure. This belief was rooted in the prevailing theory that most asteroids are essentially ‘rubble piles‘ – loose conglomerates of dust, pebbles, and larger rocks held together predominantly by gravitational forces.
When such a rubble pile accelerates its spin beyond a critical point, the binding gravitational influence is overcome by the outward centrifugal force. This phenomenon can be analogized to a Gravitron ride, where centrifugal force presses occupants against the outer wall as the ride spins.
Conversely, a singular, massive, and cohesive object placed at the center of a spinning Gravitron would remain stable. However, an aggregation of loosely bound components would fragment under similar rotational stress.
For substantial asteroids situated in the Main Belt, this critical rotational speed was theorized to occur at approximately 2.2 hours – a theoretical absolute limit proposed in the 1990s and subsequently substantiated in 2000 through observational data of the Main Belt, which revealed a scarcity of objects exceeding 150 meters in diameter with rotation periods lower than this benchmark.
This led to the prevailing conclusion that the majority of asteroids are indeed composed of loosely aggregated material, and while more structurally sound bodies might exist, they were considered to be exceptionally rare.
The Rubin Observatory’s observational campaign, conducted over nine nights between April 21 and May 5, 2025, yielded data on approximately 340,000 asteroids. From this extensive dataset, Greenstreet and her collaborators determined the rotational velocities of 76 asteroids – 75 located within the Main Belt and one in a near-Earth trajectory.
Nineteen of these celestial bodies exhibited rotational periods falling below the established spin threshold: 16 demonstrated exceptionally rapid rotation, with periods ranging from 2.2 hours down to 13 minutes, while the remaining three were classified as ultra-fast rotators, completing a revolution in under five minutes.
This constitutes a significant revelation, as most rapidly rotating asteroids identified to date are found in proximity to Earth. Asteroids within the Main Belt were generally presumed to rotate at considerably slower and more stable rates. Notably, only one of the newly discovered fast-spinning objects was a near-Earth asteroid.
While 2025 MN45 stands out as a remarkable record-breaker, the other identified asteroids warrant considerable attention. The substantial proportion of the sample that defied the predicted spin barrier suggests a potential underestimation of the number of Main Belt asteroids possessing high density and robust structural integrity.
“It is evident that this asteroid must be composed of materials exhibiting exceptionally high tensile strength to maintain its form under such rapid rotation,” states Greenstreet. “Our calculations indicate a cohesive strength comparable to that of solid rock.”
This finding is exceptionally significant. Such solid, rock-like asteroids may represent remnants of exceptionally violent cosmic collisions that occurred during the tumultuous early period of the Solar System, preserving internal structures that most asteroids have lost over eons.
This discovery bodes well for the future exploration capabilities of the Rubin Observatory, as well as for ongoing missions such as NASA’s Lucy spacecraft, which is currently en route to conduct close-up studies of asteroids.
“With potentially unique compositions, internal architectures, and/or formation histories,” the researchers conclude, “examining a substantially larger cohort of these extremely fast-rotating asteroids is highly likely to revolutionize our understanding of asteroid physical structures and their collisional pasts, and more broadly, our comprehension of the Solar System’s formation and evolution.”
These groundbreaking findings have been formally published in The Astrophysical Journal Letters.
