NASA’s Lucy spacecraft has confirmed that the asteroid Donaldjohanson exhibits a “wobbling” rotation, spinning on two distinct axes as it moves through the solar system. Data captured during a close-range flyby in April 2025 revealed the object’s elongated, two-lobed structure, which researchers at the Southwest Research Institute describe as a “peanut” shape. This discovery provides critical insights into the formation of small asteroids and serves as a vital calibration test for the spacecraft’s upcoming mission to Jupiter’s Trojan asteroids.
Why does the asteroid wobble?
The asteroid’s unstable rotation stems from its unique shape and composition. According to the study published in the journal Science, titled “The Lucy flyby of (52246) Donaldjohanson: A bilobed asteroid with tumbling rotation,” the object is roughly half a mile in diameter. Its two-lobed structure is connected by a narrow neck, creating a gravitational profile that causes the body to tumble rather than rotate smoothly. Simone Marchi, the mission’s deputy principal investigator, confirmed that Lucy’s imagery validated these characteristics, which were initially theorized by astronomers using Earth-based telescopes.
The Donaldjohanson asteroid is named after the paleoanthropologist who discovered “Lucy,” the famous fossilized skeleton of an early human ancestor. The mission itself is named in honor of that discovery.
What is the origin of the “peanut” shape?
The asteroid’s physical makeup suggests a violent history. Researchers identified iron-rich clay minerals on the surface, which typically form in the presence of liquid water. This evidence leads scientists to believe that Donaldjohanson is a fragment of a much larger, water-rich parent asteroid. The current structure likely formed approximately 155 million years ago following a massive collision within the main asteroid belt, which shattered the parent body and left behind the current debris.
How does this mission prepare for Jupiter’s Trojans?
The flyby of Donaldjohanson acts as a high-stakes rehearsal for the primary objective of the Lucy mission. Dr. Marchi noted that the encounter allowed the team to refine instruments and operational procedures before reaching the Trojan asteroids—two massive swarms of ancient space rocks orbiting near Jupiter. Because the Trojans have remained largely undisturbed since the dawn of the solar system, they act as a “time capsule.” Studying them will likely force researchers to re-evaluate current models of how our solar system formed.
Frequently Asked Questions
- Is the Donaldjohanson asteroid dangerous?
No. The asteroid is a small, half-mile-wide object in the main asteroid belt and poses no threat to Earth. - Why is it called a “wobbling peanut”?
The description refers to its visual appearance—two lobes connected by a narrow neck—and its complex, tumbling rotation caused by its irregular shape. - When will Lucy reach the Trojan asteroids?
The mission is currently utilizing flybys of smaller objects like Donaldjohanson to calibrate its systems for the upcoming, more complex encounters with the Jupiter-bound swarms.
Have you been following the progress of the Lucy spacecraft? Share your thoughts on what these ancient space rocks might reveal about our origins in the comments section below.
