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Recent modeling led by the Southwest Research Institute suggests that the asteroid (52246) Donaldjohanson was formed approximately 150 million years ago when a larger parent asteroid fragmented. Since then, its orbital characteristics and rotation have changed significantly. When NASA’s Lucy spacecraft conducts a flyby of this three-mile-wide asteroid on April 20, 2025, the data gathered could reveal valuable insights into its formation processes, as well as details about its shape, surface geology, and the history of cratering.
“Based on observations from Earth, Donaldjohanson is a rather unusual astronomical body,” remarked Dr. Simone Marchi of SwRI, who serves as the deputy principal investigator for the Lucy mission and authored research published in The Planetary Science Journal. “Gaining insights into its formation can clarify why it is so distinctive.”
“The findings suggest it has an elongated shape and rotates slowly, a characteristic likely influenced by thermal torques that have decelerated its rotation over time,” noted David Vokrouhlický, a professor at Charles University in Prague, and co-author of the study.
Lucy’s mission focuses on examining a typical type of asteroid composed mainly of silicate rocks, possibly enriched with clays and organic materials. The latest research indicates that Donaldjohanson is likely part of the Erigone collisional family of asteroids, formed from the remnants of a larger asteroid collision. This family resides in orbits similar to those of near-Earth asteroids (101955) Bennu and (162173) Ryugu, both of which have been closely studied by NASA’s OSIRIS-REx and JAXA’s Hayabusa2 missions.
“The upcoming flyby excites us because, based on current characteristics, Donaldjohanson appears quite different from Bennu and Ryugu, and we may discover unexpected relationships,” Marchi added.
The naming of Donaldjohanson honors the paleontologist known for discovering Lucy, the fossil of an early hominin found in Ethiopia in 1974, which inspired the name of the Lucy mission. This connection highlights the mission’s goal of enhancing our understanding of the origins of our planet, much like the fossil has enriched our knowledge of human evolution. Notably, Donaldjohanson is the only asteroid with a name that is still alive.
“The Lucy mission is an ambitious endeavor by NASA, aspiring to examine 11 asteroids over 12 years, specifically targeting the Trojan asteroids that are positioned in two groups ahead of and behind Jupiter,” stated Dr. Hal Levison from SwRI, the principal investigator of the mission. “Interacting with main belt asteroids not only affords a close examination of these celestial bodies but also serves as an opportunity to test the spacecraft’s innovative navigation system ahead of the main study of the Trojan asteroids. These objects are essentially fossils from the formation of our solar system, offering crucial insights into our cosmic history.”
Lucy’s principal investigator operates from the Boulder, Colorado branch of the Southwest Research Institute, which is based in San Antonio. NASA’s Goddard Space Flight Center in Greenbelt, Maryland, oversees the overall management of the mission, including systems engineering and safety measures. The spacecraft itself was constructed by Lockheed Martin Space in Littleton, Colorado. Lucy represents the 13th mission in NASA’s Discovery Program, which is managed by NASA’s Marshall Space Flight Center in Huntsville, Alabama, under the agency’s Science Mission Directorate.
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