SEATTLE, USA, Oct. 6, 2026 - Asteroid 491384 is the largest ultra-fast spinning asteroid known, according to a study of data from the Vera C. Rubin Observatory.^[1][2] It is about 2.53 kilometres across and completes one full rotation every 4.18 minutes.^[3] A team led by Dmitrii Vavilov at the University of Washington developed software that filters out unreliable spin-rate measurements.^[4] Applied to 9,417 asteroids observed by Rubin, it identified 66 super-fast rotators.^[5][6] Two of them, 491384 and 566130, are more than 2 km wide yet rotate in about five minutes.^[7] Asteroids larger than 150 metres are not expected to rotate faster than once every 2.2 hours if they are loose rubble piles held together only by gravity.^[8] Impact Insight. Many asteroids are thought to be rubble piles, loose collections of rock held together mainly by their own weak gravity, so a large one spinning in minutes must have some internal strength. How strongly an asteroid holds together matters for planetary defense, because it helps decide whether a deflecting impact would nudge it as a whole or break it apart, and surveys like Rubin's will measure such properties for thousands of objects.