Data from the European Space Agency’s Gaia mission has led to the development of a new framework for understanding how asteroids tumble during their journey through space, which could be crucial for future planetary defense deflection missions.
The work was presented at the EPSC-DPS2025 Joint Meeting held in September in Helsinki. In the team’s research, they revealed that the frequency with which an asteroid has experienced collisions is the primary driver for its behavior, such as whether it exhibits an ordered spin or chaotic tumble, followed by the influence of sunlight.
ESA’s Gaia Mission Data
“By leveraging Gaia’s unique dataset, advanced modeling 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,” said Dr Wen-Han Zhou of the University of Tokyo, who presented the results at EPSC-DPS2025.
Gaia collected a tremendous amount of asteroid observations focused on the space rocks’ light curves. As asteroids rotate, the light they reflect changes to a measurable degree. When researchers plotted the rotational speed against an asteroid’s diameter, they observed the emergence of two distinct populations in the data. The new work finally addresses the cause of the mysterious gap between these two groups of asteroids.
“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,” said Zhou. “When these two effects balance, they create a natural dividing line in the asteroid population.”
After comparing predictions from their model to real-world data, they found that the two matched.
Chaos and Order in Asteroids
What separates the two groups is the unexpected tendency for asteroids to either exhibit a slow but chaotic tumble or a faster, neater spin. The high number of tumbling asteroids and the propensity of smaller asteroids to tumble slowly have long confused scientists.
According to Zhou’s recent study, sunlight and collisions are driving factors in asteroid behavior. When an asteroid spins slowly, it is more likely to be affected by collisions, which can cause the asteroid to tumble chaotically.
Usually, sunlight’s subtle influence on asteroids evens out their motion into a neat spin. This occurs as the asteroid absorbs sunlight and emits it back out as photons, which then gently nudge the asteroid. While these tiny pushes can speed up or slow down an asteroid’s spin, they typically maintain a tight spin as the direction of the photons remains constant.
Tumbling asteroids, though, experience a much weaker version of this effect, as their chaotic motion doesn’t allow the continually unidirectional push of protons to build up to a significant impact on the asteroid. Instead, the rotation changes very slowly, resulting in a slow-rotating group of asteroids, as evident in the data.
Informing Planetary Defense
By combining this new knowledge with existing understanding of how an asteroid’s internal structure affects its spin, researchers can better understand how asteroids are made up. The data suggest that most asteroids are composed of loose rubble held together by gravity and covered in a thick layer of dust called regolith, rather than being solid 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,” said Zhou.
Understanding this makeup is essential to deflection missions. While NASA’s DART mission has already succeeded in changing the course of an asteroid, whether the body to be deflected is a loose pile of rubble or solid rock will have a significant effect on how it behaves under a kinetic impact. Armed with this more detailed understanding of how asteroids are composed and how external factors influence them, future planetary defense missions will be able to plan with increased accuracy.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.