Overview
- Lucy flew past asteroid (52246) Donaldjohanson on April 20, 2025, and scientists have now analyzed the data to reveal its rotation and composition.
- The asteroid is in a non-principal-axis tumble with a primary spin of 10.5 Earth days and a secondary wobble of 26.5 Earth days.
- Researchers attribute the complex spin to the object's asymmetric, peanut-like shape combined with the YORP effect, a torque from uneven heating and sunlight.
- Spectral measurements detected iron-rich phyllosilicate (clay) minerals that imply brief past exposure to liquid water and suggest Donaldjohanson is a fragment from a larger water-rich parent that broke up about 155 million years ago.
- The findings help place Donaldjohanson with other water-altered bodies like Bennu and Ryugu, refine models of its spin history and collisional past, and serve as a dress rehearsal for Lucy's scheduled Jupiter Trojan flybys beginning in summer 2027.