When NASA’s Lucy spacecraft swept past the asteroid Donaldjohanson on April 20, 2025, it caught more than just surface details—it revealed a cosmic dancer spinning off-kilter through the void. The 0.8-kilometer-wide asteroid, named after the paleoanthropologist who discovered the ancient human ancestor Lucy, doesn’t rotate smoothly like most small bodies in space. Instead, it tumbles end over end every 10.5 Earth days while wobbling around a secondary axis every 26.5 days, a motion known as tumbling rotation. This unexpected behavior, captured during Lucy’s flyby of the inner main-belt asteroid, is now reshaping how scientists understand the dynamics of small celestial bodies.
The discovery matters because Donaldjohanson is more than just a space rock—it’s a relic from a violent chapter in our solar system’s history. Data from Lucy’s infrared spectrometer revealed iron-rich clay minerals on its surface, chemical fingerprints of liquid water that once existed within its parent body. These clays closely resemble those found in carbon-rich meteorites like QUE 97990, suggesting Donaldjohanson formed from debris after a massive collision 155 million years ago in the asteroid belt between Mars and Jupiter. That impact shattered a larger, water-laden asteroid, scattering fragments that eventually coalesced into objects like this peanut-shaped remnant.
SwRI’s Dr. Simone Marchi, deputy principal investigator of the Lucy mission and lead author of the study published in Science, called the encounter “just one of many surprising things” uncovered so far. The spacecraft’s images confirmed earlier hints from Earth-based telescopes: Donaldjohanson has a two-lobed structure connected by a narrow neck, resembling a stretched peanut. This shape likely contributes to its unstable spin, a clue to the chaotic forces that shaped it.
But Lucy’s visit wasn’t just about studying one asteroid—it was a dress rehearsal. The mission’s primary target lies farther out: the Trojan asteroids, two swarms that orbit the Sun ahead of and behind Jupiter, thought to be primordial remnants from the solar system’s formation. By testing instruments and procedures on Donaldjohanson, the team ensured they’re ready for what comes next. “Once we start learning more about the Trojans, a completely different population of space rocks with very different histories, our understanding of solar system formation is likely to be challenged,” Marchi said.
As the spacecraft continues its journey, the wobbling dance of Donaldjohanson serves as both a warning and an invitation: the solar system is full of surprises, and even the smallest bodies carry stories of ancient collisions, hidden water, and the enduring chaos of cosmic evolution.