NASA's Lucy Spacecraft Reveals Donaldjohanson Asteroid's Complex Wobbling Rotation and Peanut Shape

NASA's Lucy spacecraft has made a remarkable discovery during its close flyby of the asteroid Donaldjohanson on April 20, 2025, revealing a celestial body with unexpected complexity. Passing within 650 miles of the asteroid, Lucy captured the first high-resolution images and data showing that Donaldjohanson exhibits a unique two-axis rotation pattern, wobbling like a spinning top rather than rotating on a single axis like most asteroids and planets. The asteroid rotates end-over-end once every 10.5 Earth days while simultaneously wobbling around its long axis once every 26.5 days—a pattern not visible from Earth-based telescopes that only showed regular light fluctuations.

The spacecraft's imaging revealed Donaldjohanson's distinctive peanut or "bilobate" structure, consisting of two lobes connected by a narrow neck. Scientists believe these two lobes are fragments from an ancient asteroid collision approximately 155 million years ago that gently coalesced through their mutual gravitational attraction. The asteroid's surface displays numerous craters and ridges bearing the marks of its complex geological history. Researchers estimate that Donaldjohanson has slowed significantly from its original rotation rate over the past 20 to 60 million years, likely due to the YORP effect—a subtle consequence of solar heating where infrared radiation from the asteroid's sun-warmed surface creates a net torque that gradually changes its spin.

Analysis of mineral signatures detected by Lucy's instruments revealed iron-rich clay minerals on Donaldjohanson's surface, indicating that liquid water once played a role in the asteroid's geological processes in the distant past. However, the water's presence appears to have been fleeting, as the magnesium replacement patterns in the clays suggest only brief exposure to liquid water. The encounter served as a successful dress rehearsal for Lucy's mission systems before the spacecraft's primary objectives begin with its August 12, 2027 flyby of the Trojan asteroid Eurybates. Scientists also used the opportunity to compare Donaldjohanson with other studied asteroids including Bennu and Ryugu, adding valuable data to humanity's understanding of asteroid composition and evolution.