Although NASA’s Lucy spacecraft’s upcoming encounter with the asteroid Donaldjohanson is primarily a mission rehearsal for later asteroid encounters, a new paper suggests that this small, main belt asteroid may have some surprises of its own. New modeling indicates that Donaldjohanson may have been formed about 150 million years ago when a larger parent asteroid broke apart; its orbit and spin properties have undergone significant evolution since.
When the Lucy spacecraft flies by this approximately three-mile-wide space rock on April 20, 2025, the data collected could provide independent insights on such processes based on its shape, surface geology and cratering history.
“Based on ground-based observations, Donaldjohanson appears to be a peculiar object,” said Simone Marchi, deputy principal investigator for Lucy of Southwest Research Institute in Boulder, Colorado and lead author of the research published in The Planetary Science Journal. “Understanding the formation of Donaldjohanson could help explain its peculiarities.”
“Data indicates that it could be quite elongated and a slow rotator, possibly due to thermal torques that have slowed its spin over time,” added David Vokrouhlický, a professor at the Charles University, Prague, and co-author of the research.
Lucy’s target is a common type of asteroid, composed of silicate rocks and perhaps containing clays and organic matter. The new paper indicates that Donaldjohanson is a likely member of the Erigone collisional asteroid family, a group of asteroids on similar orbits that was created when a larger parent asteroid broke apart. The family originated in the inner main belt not very far from the source regions of the near-Earth asteroids Bennu and Ryugu, recently visited respectively by NASA’s OSIRIS-REx and JAXA’s (Japan Aerospace Exploration Agency’s) Hayabusa2 missions.
“We can hardly wait for the flyby because, as of now, Donaldjohanson’s characteristics appear very distinct from Bennu and Ryugu. Yet, we may uncover unexpected connections,” added Marchi.
“It’s exciting to put together what we’ve been able to glean about this asteroid,” said Keith Noll, Lucy project scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “But Earth-based observing and theoretical models can only take us so far – to validate these models and get to the next level of detail we need close-up data. Lucy’s upcoming flyby will give us that.”
Donaldjohanson is named for the paleontologist who discovered Lucy, the fossilized skeleton of an early hominin found in Ethiopia in 1974, which is how the Lucy mission got its name. Just as the Lucy fossil provided unique insights into the origin of humanity, the Lucy mission promises to revolutionize our knowledge of the origin of humanity’s home world. Donaldjohanson is the only named asteroid so far to be visited while its namesake is still living.
“Lucy is an ambitious NASA mission, with plans to visit 11 asteroids in its 12-year mission to tour the Trojan asteroids that are located in two swarms leading and trailing Jupiter,” said SwRI’s Dr. Hal Levison, mission principal investigator at the Boulder, Colorado branch of Southwest Research Institute in San Antonio, Texas. “Encounters with main belt asteroids not only provide a close-up view of those bodies but also allow us to perform engineering tests of the spacecraft’s innovative navigation system before the main event to study the Trojans. These relics are effectively fossils of the planet formation process, holding vital clues to deciphering the history of our solar system.”
Lucy’s principal investigator is based out of the Boulder, Colorado, branch of Southwest Research Institute, headquartered in San Antonio. NASA’s Goddard Space Flight Center in Greenbelt, Maryland, provides overall mission management, systems engineering, and safety and mission assurance. Lockheed Martin Space in Littleton, Colorado, built the spacecraft. Lucy is the 13th mission in NASA’s Discovery Program. NASA’s Marshall Space Flight Center in Huntsville, Alabama, manages the Discovery Program for the agency’s Science Mission Directorate in Washington.
By Deb Schmid and Katherine Kretke, Southwest Research Institute
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Nancy N. Jones
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