How the Donaldjohanson Encounter Prepared Lucy for Jupiter Trojans
Lucy’s April 2025 flyby of asteroid Donaldjohanson returned science data and exercised the spacecraft, instruments and operations before the mission’s Trojan encounters.
Timeline
- April 20, 2025: Lucy passed about 960 kilometers from asteroid Donaldjohanson.
- August 2027: Lucy is scheduled to begin its primary Jupiter Trojan encounters with Eurybates.
NASA’s Lucy spacecraft flew about 600 miles, or 960 kilometers, from the main-belt asteroid Donaldjohanson on April 20, 2025. The encounter occurred while Lucy was traveling toward the Jupiter Trojan asteroids and provided both a science opportunity and a realistic test of flyby operations. [1][2]
Donaldjohanson is not one of Lucy’s primary Trojan targets. It orbits in the main asteroid belt between Mars and Jupiter. NASA describes it as a fragment from a collision roughly 150 million years ago and named it for the anthropologist who discovered the fossil skeleton nicknamed Lucy. [1]
During a fast encounter, the spacecraft must point instruments accurately while the target’s apparent position changes quickly. Teams plan observation sequences in advance, protect the spacecraft near closest approach and then verify its health and downlink stored data. Practicing that chain before 2027 reduces operational uncertainty. [1][2]
Initial images showed an elongated contact-binary shape with two lobes joined by a narrow neck. NASA’s preliminary dimensions were about eight kilometers long and 3.5 kilometers wide at the widest point. Later downlinked observations were needed to reveal the full object because it exceeded the camera’s field of view near closest approach. [1][2]
The flyby also exercised Lucy’s science payload and tracking systems under encounter conditions. Success meant more than taking one photograph: navigation, autonomous pointing, timing, data storage, communications and instrument performance all had to work together while the spacecraft could not receive real-time steering from Earth. [1][2]
Lucy’s primary mission is to study asteroids that share Jupiter’s orbit around the Sun in two swarms. Those Trojan bodies are thought to preserve information about material and collisions from early solar-system history. Donaldjohanson offered a different object and did not substitute for the planned Trojan sequence. [1]
The first main Trojan target is Eurybates in August 2027. The Donaldjohanson encounter therefore served as a milestone between cruise and the primary campaign: it produced a scientifically valuable asteroid dataset while giving the team time to apply operational lessons before the higher-priority flybys. [1][2]