April 20, 2025: Visiting Asteroid Donaldjohanson

Why It Matters

The detailed imaging of a previously unknown contact binary refines models of asteroid formation and informs planetary‑defense strategies. It also demonstrates the cost‑effective value of repurposing deep‑space missions for secondary science targets.

Key Takeaways

• Lucy captured Donaldjohanson from 1,600 to 1,100 km
• Asteroid measures 8 km long, 3.5 km wide, larger than expected
• Shape is a peanut‑shaped contact binary with a narrow neck
• Scientists surprised by neck resembling nested ice‑cream cones
• Encounter provides clues to early solar system formation

Pulse Analysis

NASA’s Lucy spacecraft, launched in 2021 to study Trojan asteroids, performed a secondary flyby of main‑belt asteroid 52246 Donaldjohanson on 20 April 2025. Using its LOng Range Reconnaissance Imager (L’LORRII), Lucy recorded a continuous time‑lapse as it approached within roughly 920 km, delivering the clearest visual record of a small, inner‑belt object to date. The mission’s dual focus—probing both ancient planetary remnants and a newly discovered contact binary—demonstrates the versatility of deep‑space probes for opportunistic science for planetary science.

The high‑resolution images revealed Donaldjohanson’s elongated, peanut‑shaped silhouette, measuring about 8 km in length and 3.5 km at its widest point—significantly larger than pre‑encounter estimates. Its two lobes are joined by a narrow neck that resembles nested ice‑cream cones, a morphology rarely seen among small bodies. Researchers interpret this form as a contact binary, where two separate asteroids gently merged, preserving a record of low‑velocity collisions that shaped the early asteroid belt. Such detailed geometry helps refine models of accretion and internal structure.

Beyond pure science, the flyby underscores the strategic value of repurposing spacecraft for secondary targets, a practice that can lower costs while expanding data returns. Understanding contact binaries informs planetary‑defense strategies, as their weakly bound structures may respond differently to kinetic‑impact mitigation. Moreover, the mission’s naming synergy—linking the Lucy hominid discovery to the asteroid—captures public imagination, reinforcing the narrative that space exploration reveals origins both terrestrial and celestial. Future missions, such as the upcoming Psyche and Hera, will build on Lucy’s imaging techniques to probe composition and internal makeup of similar bodies.