Scientists have discovered that the inner main-belt asteroid Donaldjohanson rotates with a pronounced wobble, according to a study published in Science by Southwest Research Institute (SwRI) researchers. Rather than spinning steadily on a single axis, the space rock turns end over end while simultaneously wobbling around a second axis.
The finding came from data collected during NASA's Lucy spacecraft flyby, which provided an unprecedented close-up view of the asteroid. This complex motion, known as non-principal axis rotation, is relatively rare among asteroids and offers clues about the object's history and internal structure.
Donaldjohanson completes one end-over-end rotation every 10.5 Earth days, while its horizontal wobble cycles every 26.5 days. The two distinct periods indicate the asteroid is not a solid, rigid body but may have a rubble-pile composition, meaning it is loosely held together by gravity.
Understanding how such objects tumble helps scientists assess their stability and potential hazards. It also informs models of how asteroids evolve over time after collisions or other disruptive events. The Lucy mission continues to return data that refine knowledge of these ancient solar system remnants.
Future observations could confirm whether the wobble is damping down over time or being actively maintained by gravitational torques. The SwRI team plans to combine Lucy's data with ground-based telescopic surveys to build a more complete picture.