Asteroid rotation patterns reveal new insights into their interiors

Asteroid rotation patterns reveal new insights into their interiors
by Clarence Oxford
Helsinki, Finland (SPX) Oct 13, 2025

Whether an asteroid spins smoothly or tumbles chaotically has now been linked to its history of collisions, according to new findings from ESA's Gaia mission presented at the EPSC-DPS2025 Joint Meeting. The research provides a method to probe asteroid interiors, an advance with major implications for planetary defense strategies.

"By leveraging Gaia's unique dataset, advanced modelling and AI tools, we've revealed the hidden physics shaping asteroid rotation, and opened a new window into the interiors of these ancient worlds," said Dr Wen-Han Zhou of the University of Tokyo, who led the study.

Gaia's all-sky survey generated a vast catalogue of asteroid light curves, enabling scientists to chart their spin rates. When plotted by size and rotation, a striking gap appears, dividing slow, tumbling rotators from faster, stable spinners. Zhou's team traced this boundary to a balance between two opposing forces: collisions in the asteroid belt, which destabilize rotation, and internal friction, which gradually restores order.

Machine learning applied to Gaia's data showed that the gap aligns almost exactly with predictions from the team's new spin evolution model. Below the gap lie slow tumblers with periods under 30 hours, while above it are faster, stable rotators.

For decades, astronomers puzzled over why smaller asteroids are often found in chaotic tumbling states. The new study highlights collisions and solar heating as key factors. Slow rotators are easily jolted into tumbling by impacts, while the subtle push from absorbed and re-emitted sunlight-known as the YORP effect-fails to restore order when the spin is chaotic.

This discovery carries practical value. Rotation patterns can reveal how rigid or loose asteroid interiors are, pointing toward structures dominated by rubble piles, voids, and thick regolith blankets. Such knowledge is critical for planetary defense, since rubble pile asteroids would react differently to impact deflection attempts like NASA's DART mission than solid rock bodies.

"With forthcoming surveys like the Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST), we'll be able to apply this method to millions more asteroids, refining our understanding of their evolution and make-up," Zhou noted.

Research Report:Understanding the Long-Term Rotational Evolution of Asteroids with Gaia