NASA’s Lucy Mission Reveals Complex History of Asteroid Donaldjohanson

NASA’s Lucy spacecraft successfully completed a flyby of the asteroid 152830 Dinkinesh—referred to as Donaldjohanson in recent mission analysis—on November 1, 2023, providing the first high-resolution data on the object’s unique, bilobate structure and complex rotation. The mission, managed by the Southwest Research Institute and NASA’s Goddard Space Flight Center, confirmed the asteroid acts as a “wobbling” top, shaped by both ancient collisions and the long-term influence of solar radiation.

How Does the Asteroid Rotate?

Data collected by the Lucy spacecraft indicates that 152830 Dinkinesh does not rotate around a single, stable axis. Instead, the object exhibits a complex motion, turning end-over-end once every 10.5 days while simultaneously rocking along its long axis every 26.5 days.

According to findings published in the journal Nature, this behavior differs significantly from the simple, single-axis rotation typically observed in larger solar system bodies. Scientists attribute this motion to the YORP (Yarkovsky–O’Keefe–Radzievskii–Paddack) effect. This phenomenon occurs when sunlight absorbed by an asteroid is re-emitted as infrared radiation. Because the asteroid’s shape is irregular, this emission creates a persistent, minute recoil force that gradually alters the object’s spin rate over millions of years.

Structural Evolution and Formation

The flyby confirmed that the asteroid is bilobate, consisting of two lobes connected by a narrow neck. Researchers believe this structure formed approximately 155 million years ago when fragments from a larger parent body collision merged under the influence of mutual gravity.

As the YORP effect slowed the asteroid’s rotation over the last 20 to 60 million years, the reduction in centrifugal force caused loose surface material to shift. This migration of debris resulted in the softened appearance of craters captured in the spacecraft’s imagery. This process mirrors the evolutionary history of other near-Earth asteroids, such as Bennu and Ryugu, though those objects are estimated to be significantly older—between 1 and 2 billion years—according to NASA mission data.

Evidence of Ancient Water

Instruments aboard the Lucy spacecraft detected iron-rich clay minerals on the surface of the asteroid. The presence of these minerals serves as a geochemical indicator that the object was once exposed to liquid water.

However, researchers note that this exposure was likely brief. Unlike Bennu and Ryugu, which contain magnesium-rich clays indicative of prolonged water interaction lasting millions of years, the iron-rich composition of the clays on this asteroid suggests a more limited window of aqueous activity. This distinction provides critical evidence that these asteroids may have originated in different regions of the solar system or within parent bodies that experienced varying thermal histories.

Mission Context and Future Objectives

The flyby served as a critical operational test for the Lucy spacecraft as it continues its trajectory toward the Jupiter Trojan asteroids. By analyzing 152830 Dinkinesh, the mission team refined the systems and imaging protocols necessary for future encounters.

Comparison of Asteroid Characteristics

| Feature | 152830 Dinkinesh | Bennu / Ryugu |
| :— | :— | :— |
| Estimated Age | ~155 Million Years | 1–2 Billion Years |
| Clay Composition | Iron-rich | Magnesium-rich |
| Primary Driver | YORP Effect | YORP Effect |
| Orbital History | Main Belt | Near-Earth Migration |

The Lucy mission, which is the 13th mission in NASA’s Discovery Program, is scheduled to reach its first Trojan asteroid, Eurybates, on August 12, 2027. These Trojan asteroids are expected to provide a clearer record of the early solar system, as they have remained largely unchanged since the era of planetary formation. According to Simone Marchi, the study’s lead author at the Southwest Research Institute, comparing these diverse populations is essential for reconstructing the migration of planets and the origins of the inner solar system.