A team led by University of Washington astronomers has discovered the fastest-ever spinning asteroid with a diameter over half a kilometer. The asteroid — found while analyzing data from the NSF–DOE Vera C. Rubin Observatory and dubbed 2025 MN45 — is 0.4 miles in diameter and completes a full rotation every 1.88 minutes.
The study provides crucial information about asteroid composition and evolution. The discovery also demonstrates Rubin Observatory’s potential as it prepares for a 10-year nightly survey of the Southern Hemisphere sky, the Legacy Survey of Space and Time (LSST).
The research team published its findings January 7 in Astrophysical Journal Letters.
“It’s really exciting that in some of the very first test images taken with the Vera C. Rubin Observatory that we’re already breaking records with the discovery of the fastest-spinning large asteroid found to date,” said lead author Sarah Greenstreet, a UW affiliate assistant professor of astronomy and astronomer at NSF NOIRLab. “With millions of new asteroids expected to be found by the Rubin Observatory in the near future, this is just the beginning of many exciting discoveries yet to come.”
The study uses data collected over the course of about 10 hours across seven nights in April and May 2025, during Rubin Observatory’s early commissioning phase. That same data revealed thousands of asteroids cruising about our solar system, about 1,900 of which have been confirmed as never-before-seen. Within that flurry, Greenstreet’s team at the UW discovered 19 quickly rotating asteroids, including 2025 MN45.
As asteroids orbit the sun, they also rotate at a wide range of speeds. These spin rates not only offer clues about the conditions of their formation billions of years ago, but also tell us about their internal composition and evolution over their lifetimes. In particular, an asteroid spinning quickly may have been sped up by a past collision with another asteroid, suggesting that it could be a fragment of an originally larger object.
Fast rotation also requires an asteroid to have enough internal strength to not fly apart into many smaller pieces, called fragmentation. Most asteroids are “rubble piles,” which means they are made of many smaller pieces of rock held together by gravity, and thus have limits based on their densities as to how fast they can spin without breaking apart.
“Clearly, this asteroid must be made of material that has very high strength in order to keep it in one piece as it spins so rapidly,” Greenstreet said. “We calculate that it would need a cohesive strength similar to that of solid rock, which is quite unusual.”
Most fast rotators discovered so far orbit the sun just beyond Earth, known as near-Earth objects. Scientists find fewer fast-rotating main-belt asteroids, which orbit the sun between Mars and Jupiter, because their greater distance from Earth makes them fainter.
All but one of the newly identified fast-rotators, however, live in the main asteroid belt — an achievement made possible by Rubin’s enormous light-collecting power and precise measurement capabilities.
“As this study demonstrates, even in early commissioning, Rubin is successfully allowing us to study a population of relatively small, very rapidly rotating main-belt asteroids that hadn’t been reachable before,” Greenstreet said.
The discoveries of all 1,900 new asteroids, including the 19 fast rotators, were made possible by software developed by the UW Data-intensive Research in Astrophysics and Cosmology (or DiRAC) Institute. DiRAC’s software will power Rubin’s future solar system discoveries during its 10-year survey.
“These are exciting results but there’s much more to come,” said co-author Mario Jurić, a UW professor of astronomy. “In the next two years, Rubin will discover a thousand times as many asteroids as were presented here. Rubin’s data will open the window into what’s out there in our solar system, and how it all came to be.”
UW co-authors include Zhuofu (Chester) Li, a doctoral student in astronomy and astrobiology; Dmitrii E. Vavilov, a postdoctoral researcher in astronomy; Devanshi Singh, an undergraduate student of physics and astronomy at UW Bothell; Željko Ivezić, a professor of astronomy; Joachim Moeyens, a software engineer in astronomy; Eric C. Bellm, a research associate professor of astronomy; Jacob A. Kurlander, a graduate student of astronomy; Maria T Patterson and Nima Sedaghat, who worked on this study as research scientists in astronomy; Krzysztof Suberlak, a research scientist in astronomy; and Ian S. Sullivan, a senior research scientist in astronomy. A full list of co-authors is included with the paper.
This research was funded by the U.S. National Science Foundation and the U.S. Department of Energy. The DiRAC Institute is supported by the Charles and Lisa Simonyi Fund for Arts and Sciences, Janet and Lloyd Frink and the Washington Research Foundation.
For more information, contact Greenstreet at sarahjg@uw.edu.
This story was adapted from a press release by Vera C. Rubin Observatory.