Two large asteroids rotate in minutes, implying unusual internal strength
Two independent reports describe unusually rapid rotation in two kilometre-scale asteroids identified in Rubin Observatory survey data. A preprint estimates that their material needs substantial internal cohesion to survive spins lasting only minutes. The result challenges expectations for loosely bound rubble piles, while remaining an interpretation of brightness measurements: the rotation periods need independent observations, and the objects’ internal structure has not been directly measured.
Science··Evening
Minute-long spins in kilometre-scale bodies
Two large asteroids identified in survey data complete rotations in only minutes, according to independent reporting by scinexx and New Scientist. The underlying preprint, which has not undergone peer review, analyses observations from the Vera C. Rubin Observatory, a wide-field astronomical survey facility. Asteroid 491384 has an estimated diameter of 2.53 kilometres and a rotation period of 4.18 minutes. Asteroid 566130 measures an estimated 1.99 kilometres and turns in 5.34 minutes. Their combination of size and rapid rotation challenges the familiar picture of an asteroid as a loosely bound collection of fragments. The analysis does not directly image either interior.[1], [2]
A method that adjusts to each light curve
The researchers examined 9,417 asteroids with at least 80 brightness measurements each, collected from April 2025 to January 2026. As an irregular object rotates, its reflected sunlight changes. The method fits those variations using a Fourier series, a combination of repeating mathematical waves, with its complexity chosen for each object. Reliability tests assess competing period solutions rather than automatically accepting the fastest candidate. The selected sample contained 66 reliable candidates rotating faster than the customary 2.2-hour spin barrier. A fixed-order method doubled the inferred period of asteroid 491384, illustrating why the light-curve model matters. New Scientist also reports Vavilov’s account of the sample and rapid rotators, while scinexx describes the varying-order approach.[1], [2]
Internal strength inferred from survival at high speed
The estimated spins require substantial cohesion if the objects are to resist breaking apart. The preprint gives minimum estimates of 2.3 megapascals for 491384 and 0.9 megapascals for 566130. New Scientist’s interview discusses stronger internal material, while scinexx describes rock-like strength. These interpretations allow a coherent or cemented structure but do not establish that each asteroid is a single solid rock. Diameters are inferred from brightness and assumed reflectivity, and additional independent observations are needed to confirm the periods. The study also leaves the origin of the rapid spins unresolved. Sunlight-driven torques are a possible explanation discussed in the reporting, without direct observation of that mechanism in these particular objects.[1], [2]
