Scientists studying the inner main belt asteroid 52246 Donaldjohanson, believed to be a member of the Erigone asteroid family, have found that its rotation wobbles. Donaldjohanson is named for the paleontologist Donald Johanson, who discovered “Lucy,” the fossilized skeleton of an early hominin found in Ethiopia in 1974, while the Lucy mission itself is named after that human ancestor.
DJ turns on two axes, rotating end over end every 10.5 days. Even more interesting, it wobbles around its horizontal axis every 26.5 days. This was a surprise to scholars expecting it to be rolling through space in a steady pattern. The Lucy mission that detected this pattern in April of 2025 also confirmed an elongated shape, like a peanut, suggsted by telescopes. DJ is only half a mile in diameter but that it one big, wobbly peanut.
During its April 20, 2025, encounter with the main belt asteroid Donaldjohanson, NASA’s Lucy spacecraft discovered evidence for iron-rich clays on the surface of the asteroid using its infrared spectrometer. Recent studies led by SwRI scientists found that the clays are similar to those found in carbon-rich meteorites such as QUE 97990 and indicate the presence of water on the asteroid in the distant past. Credit: NASA/Goddard/SwRI/Dan Gallagher Image of Donaldjohanson: NASA/Goddard/SwRL/JHU-APL
Data reveal it contains iron-rich clay minerals, formed long ago due to liquid water, which means it is almost certain to have been part of a larger carbon- and water-rich asteroid that broke apart 155 million years ago, following a collision in the main asteroid belt, the region between Mars and Jupiter.
Lucy’s primary mission is to explore the Trojan asteroids, two leading and trailing swarms of ancient objects around Jupiter as it orbits the Sun. The hope is the analyses of the ancient space rocks will reveal new insights about the early history of the solar system.
Citation: The Lucy flyby of (52246) Donaldjohanson: A bilobed asteroid with tumbling rotation.Science392,1287-1291(2026). DOI: 10.1126/science.aec0503
