Gaia mission reveals causes of tumbling asteroids
Scientists using data from the European Space Agency's Gaia mission have explained why some asteroids tumble chaotically while others spin steadily, linking it to collision frequency. The findings, presented at the EPSC-DPS2025 Joint Meeting in Helsinki, show a gap in rotation speeds that divides asteroid populations and indicates most are loose rubble piles. This could improve strategies for deflecting hazardous asteroids.
The European Space Agency's Gaia mission has provided unprecedented insights into asteroid behavior by analyzing light curves from its sky survey. These curves track how an asteroid's reflected light changes as it rotates, revealing rotation periods and patterns. When plotted against asteroid diameter, the data reveals a clear gap separating two groups: slowly tumbling asteroids with periods under 30 hours below the gap, and faster, stable spinners above it.
Dr. Wen-Han Zhou of the University of Tokyo, who led the study while at the Observatoire de la Côte d'Azur in France, presented the results at the EPSC-DPS2025 Joint Meeting in Helsinki. His team developed a model balancing collisions in the asteroid belt, which induce tumbling, against internal friction that restores stable rotation. "We built a new model of asteroid-spin evolution that considers the tug of war between two key processes, namely collisions in the Asteroid Belt that can jolt asteroids into a tumbling state, and internal friction, which gradually smooths their spin back to a stable rotation," Zhou explained. "When these two effects balance, they create a natural dividing line in the asteroid population."
Machine learning applied to Gaia's asteroid catalog confirmed the model's predictions. Collisions often start tumbling in slowly rotating asteroids, while the YORP effect from sunlight accelerates smooth spinners but has a muted impact on tumblers due to their chaotic motion. The analysis supports asteroids as rubble piles with voids and dusty regolith, rather than solid bodies.
This understanding has implications for planetary defense. A rubble pile would respond differently to impacts like NASA's DART mission compared to a rigid asteroid. Zhou noted, "By leveraging Gaia's unique dataset, advanced modelling and A.I. tools, we've revealed the hidden physics shaping asteroid rotation, and opened a new window into the interiors of these ancient worlds." Future surveys, such as the Vera C. Rubin Observatory's LSST, could extend this to millions more asteroids.