NASA's Lucy spacecraft has unveiled surprising details about asteroid Donaldjohanson, revealing it to be a peanut-shaped, wobbling relic drifting through the inner asteroid belt. Researchers at the Southwest Research Institute published their findings in the journal Science on June 18, 2026, based on data collected during Lucy's flyby of the asteroid on April 20, 2025. The asteroid, measuring roughly 800 meters or about half a mile in diameter, consists of two large lobes connected by a narrow neck, giving it its distinctive peanut-like silhouette.
The study reveals a complex and unusual rotational behavior that sets Donaldjohanson apart from most known asteroids. The body rotates end-over-end every 10.5 Earth days, while simultaneously wobbling on its horizontal axis in a cycle that repeats every 26.5 days. This dual motion creates an intricate tumbling pattern as the asteroid travels along its orbit around the Sun, making it one of the more dynamically interesting objects scientists have encountered in the belt.
According to the researchers, Donaldjohanson formed approximately 155 million years ago from fragments produced by a violent collision between larger bodies. Over immense spans of time, these scattered pieces gradually drifted together under the influence of mutual gravity, eventually merging into the bilobed shape observed today. The process, known as gentle accretion, helps explain why the asteroid retains such a distinct two-lobed structure rather than forming a more uniform sphere.
A subtle but persistent force generated by sunlight, known as the Yarkovsky-O'Keefe-Radzievskii-Paddack effect or YORP effect, has played a significant role in altering the asteroid's rotation over millions of years. As sunlight strikes the irregularly shaped surface and is re-emitted as thermal radiation, it creates tiny torques that slowly shift the spin axis and speed. This mechanism is believed to be responsible for driving Donaldjohanson into its current tumbling state, a finding that provides valuable data for understanding how small bodies evolve dynamically in the solar system.
Perhaps most remarkably, traces of ancient water remain preserved within the rocky surface of Donaldjohanson. This discovery suggests that the parent body from which the asteroid originated once contained hydrated minerals, offering a window into the conditions that prevailed in the early solar system billions of years ago. Scientists believe these water signatures could help refine models of how water and other volatile compounds were distributed across the young solar system.
The asteroid is named after paleoanthropologist Donald Johanson, who discovered the famous Lucy fossil in Ethiopia in 1974. The NASA mission itself takes its name from this celebrated hominin skeleton, drawing a symbolic connection between exploring human origins on Earth and investigating the origins of the solar system. Donaldjohanson was the first asteroid target on Lucy's ambitious 12-year journey to study the Trojan asteroids that share Jupiter's orbit.
Looking ahead, the Lucy spacecraft will continue its voyage toward the Trojan asteroid swarms, with its next encounters expected in the coming years. The wealth of data gathered from the Donaldjohanson flyby has already exceeded expectations, giving planetary scientists fresh insights into the formation, evolution, and composition of primitive solar system bodies. Mission leaders have expressed confidence that future flybys will yield equally groundbreaking results as Lucy charts a course through some of the least explored regions of our cosmic neighborhood.
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