What asteroid did NASA's Lucy mission fly by in April 2025, revealing it to be a contact binary?

NASA's Lucy mission made an exciting discovery in April 2025 when it flew past asteroid (52246) Donaldjohanson, revealing it to be a contact binary. The spacecraft conducted its close flyby of this main-belt asteroid on April 20, 2025, coming within approximately 960 kilometers (600 miles) of its surface. Images returned by Lucy confirmed that Donaldjohanson is composed of two distinct lobes connected by a narrow neck, appearing somewhat like two nested ice cream cones. This unique shape indicates that it formed from two smaller asteroids that gently collided and merged, rather than breaking apart.

The Lucy mission is primarily designed to explore the Trojan asteroids, a population of primordial objects orbiting Jupiter that are considered "fossils" of the early solar system. Donaldjohanson, however, is located in the main asteroid belt between Mars and Jupiter and served as a crucial engineering test or "dress rehearsal" for Lucy's more distant encounters with the Trojans. The asteroid itself is named after paleoanthropologist Donald Johanson, who discovered the fossilized hominin skeleton "Lucy," after which the mission is also named.

The discovery of Donaldjohanson as a contact binary adds to our understanding of how asteroids form and evolve. It follows a similar finding from Lucy's first flyby target, Dinkinesh, and its moon Selam, which was also revealed to be a contact binary. These observations support the growing hypothesis that such binary systems are more common in the main asteroid belt than previously thought. Studying the complex geology of Donaldjohanson helps scientists decipher the collisional processes that shaped countless other asteroids and contributed to the formation of planets in our solar system.