NASA’s Lucy spacecraft confirmed that the asteroid Donaldjohanson is a fragment of the ancient Erigone family, formed by a massive collision 155 million years ago. Data published in the journal Science by a team led by Simone Marchi of the Southwest Research Institute shows the asteroid possesses a peanut-like shape and iron-bearing minerals, indicating it originated from a 50-mile-wide parent body.
How did Donaldjohanson form?
According to the study published in Science, Donaldjohanson is the result of a violent impact that shattered a much larger parent asteroid. Researchers estimate this parent body measured roughly 50 miles (80 kilometers) in diameter. When a smaller, 12-mile-wide space rock struck it 155 million years ago, the resulting debris scattered across the solar system. The asteroid’s current peanut shape, featuring two lobes connected by a smooth neck, suggests these pieces later accreted into the structure Lucy observed during its April 2025 flyby.
The asteroid is named after Donald Johanson, the paleoanthropologist who discovered the famous “Lucy” fossil in 1974. NASA’s spacecraft shares the same namesake.
What do the surface features reveal about asteroid history?
Lucy’s high-resolution imagery revealed a cratered surface that tells a story of both age and recent activity. Simone Marchi’s team noted that while the density of craters aligns with the 155-million-year age of the Erigone family, there is a distinct lack of small craters under 0.2 miles (0.4 kilometers) wide. This suggests that the asteroid underwent a more recent event, likely seismic shaking from a secondary impact, which smoothed out the smaller surface features.
How does Donaldjohanson compare to other asteroids?
The composition of Donaldjohanson offers a stark contrast to other space rocks visited by the mission. While the Dinkinesh asteroid, visited by Lucy in November 2023, revealed itself as a complex binary system with its own moon, Donaldjohanson provides evidence of water-rich origins. The detection of iron-bearing phyllosilicates indicates that the asteroid’s parent body contained liquid water in its early history, which chemically altered the minerals present on the rock’s surface.
Keep an eye on the 2027 mission milestones. Lucy is scheduled to begin its primary tour of the Trojan asteroids, which are expected to yield even more diverse data than the main belt rocks visited so far.
Why does tracking these fragments matter?
Understanding these space rocks helps scientists map the evolution of the solar system. By tracing fragments like Donaldjohanson back to their parent bodies, researchers can constrain the timeline of collisions that shaped the near-Earth environment. This data serves as a blueprint for how asteroids migrate and evolve over hundreds of millions of years. NASA’s ongoing mission, which spans a 12-year journey, aims to use these encounters to piece together the history of the materials that formed our planetary neighborhood.
Frequently Asked Questions
How close did Lucy get to Donaldjohanson?
During the April 2025 flyby, the spacecraft came within 600 miles (960 kilometers) of the asteroid, according to NASA mission reports.
What is the Erigone family?
The Erigone family is a group of nearly 1,800 primitive, water-rich asteroids in the main belt that are believed to have originated from a single, large parent body.
What is the next target for the Lucy spacecraft?
After its main belt encounters, Lucy will begin exploring the Trojan asteroids in 2027, starting with Eurybates and its moon, Queta.
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