Donaldjohanson is a main-belt asteroid that may be the remnant of a cosmic collision 150 million years ago. Scientists believe its unique shape and slow rotation may have been formed by thermal forces over time. As NASA's Lucy spacecraft prepares for a flyby in 2025, researchers hope to uncover new clues about its origins and its connections to other asteroids.

This artist's concept compares the approximate size of Lucy's next asteroid target, Donaldjohanson, to the smallest main-belt asteroids previously visited by the spacecraft (Dinkinesh and Steins, visited by Lucy in November 2023), as well as two recently explored near-Earth asteroids, Bennu and Ryugu. Lucy is a NASA mission led by SwRI that plans to visit 11 asteroids over 12 years, culminating in the first encounter with Jupiter's Trojan asteroids. Image source: SwRI/ESA/OSIRIS/NASA/Goddard/JohnsHopkinsAPL/NOIRLab/University of Arizona/JAXA/University of Tokyo and collaborators

The asteroid visit, named for the paleontologist who discovered the famous Lucy fossil, is part of an ambitious mission to explore Jupiter's Trojan asteroids and decipher the history of the solar system.

Scientists at the Southwest Research Institute (SwRI) have developed new models that suggest the main-belt asteroid (52246) Donaldjohanson may have formed about 150 million years ago when a larger asteroid broke apart. Since then, its orbit and rotation have undergone significant changes. On April 20, 2025, NASA's Lucy spacecraft will fly by the three-mile-wide asteroid, collecting data that can provide new insights into its formation and evolution by analyzing its shape, surface geology and crater history.

"Based on ground-based observations, Donaldjohanson appears to be an exotic object," said Dr. Simone March of Southwest Research Institute, deputy principal investigator of the Lucy mission led by Southwest Research Institute and lead author of the study published in the Journal of Planetary Science. "Understanding its formation helps explain its strangeness."

David Vokrouhlický, a professor at Charles University in Prague and co-author of the study, added: "The data suggest that it was probably quite elongated and rotated very slowly, possibly because thermal torque slowed its rotation over time."

NASA's Lucy mission launched on October 16, 2021, to conduct the first reconnaissance of the Trojan asteroids, a group of primitive asteroids that orbit Jupiter. In this artist's concept (not to scale), the Lucy spacecraft flies past Eurybatus, a diverse and scientifically important group of Trojan asteroids awaiting study. Image source: Southwest Research Institute

Lucy's target is a common asteroid composed of silicate rocks that may contain clay and organic matter. The new paper points out that Donaldjohanson is likely to be a member of the Errigone collision asteroid family, a group of asteroids with similar orbits that were formed by the breakup of a larger parent asteroid. This family originated in the inner main belt, not far from the source regions of the near-Earth asteroids (101955) Bennu and (162173) Ryugu, both of which were recently visited by NASA's OSIRIS-REx and the Japan Aerospace Exploration Agency's Hayabusa2 missions respectively.

"We can't wait to see it fly by because, so far, asteroid Donaldjohanson has very different characteristics than Bennu and Ryugu. However, we may discover unexpected connections," March said.

Donaldjohanson is named after the paleontologist who discovered Lucy, an early human fossil skeleton found in Ethiopia in 1974 and for which the Lucy mission is named. Just as the Lucy fossils have provided unique insights into human origins, the Lucy mission promises to revolutionize our understanding of the origins of our homeland. Donaldjohanson is the only named asteroid that has not been visited while its namesake was still alive.

"Lucy is an ambitious mission from NASA that plans to visit 11 asteroids over the course of a 12-year mission to survey two groups of Trojan asteroids located in front and behind Jupiter," said SwRI's Dr. Hal Levison, the mission's principal investigator. "Encounters with main-belt asteroids not only allow us to observe these objects up close, but also allow us to conduct engineering tests of the spacecraft's innovative navigation systems before studying the main events of the Trojan asteroids. These relics are actually fossils of the planet formation process and provide important clues for deciphering the history of the solar system."

Compiled from /ScitechDaily