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Lucy Donaldjohanson Flyby: What Happened in April 2025

NASA's Lucy spacecraft passed about 600 miles from main-belt asteroid Donaldjohanson on April 20, 2025, collecting close images and rehearsing operations for its later Jupiter Trojan encounters.

Timeline

  1. April 20, 2025, 1:51 p.m. EDT: Lucy made its closest approach to Donaldjohanson at approximately 600 miles.
  2. April 20–27, 2025: The spacecraft returned its encounter data to Earth over several days.
  3. August 2027: Lucy is scheduled to begin its primary Trojan-asteroid encounters with Eurybates.

NASA's Lucy spacecraft flew past asteroid Donaldjohanson on April 20, 2025, reaching closest approach at about 1:51 p.m. EDT. NASA reported a planned separation of approximately 600 miles, or 960 kilometers. The spacecraft contacted Earth after the encounter in good health and began transmitting the stored images and measurements over the following days. [1][2]

Donaldjohanson is in the main asteroid belt between Mars and Jupiter. It is named for anthropologist Donald Johanson, who discovered the fossil skeleton nicknamed Lucy; the spacecraft takes its name from the same fossil. Scientists think the asteroid formed from collision fragments about 150 million years ago, making it comparatively young in solar-system terms. [1]

The first detailed images showed an elongated body with two lobes joined by a narrow, unusual neck. Preliminary measurements placed it at roughly five miles long and about two miles wide at its broadest point. The nearest high-resolution images overfilled the camera's field of view, so more distant frames were needed to reconstruct the whole shape. [1][3]

Lucy used its L'LORRI high-resolution camera and other instruments while moving past the asteroid at high relative speed. The apparent change in Donaldjohanson's orientation in the rapid image sequence came largely from the spacecraft's motion. Later analysis could combine images from different angles to study craters, ridges, shape and the asteroid's complex rotation. [1][3]

The encounter was a full dress rehearsal for Lucy's primary mission. The team ran a dense observation sequence and allowed the terminal tracking system to keep the target inside the instruments' fields of view while the antenna turned away from Earth. Practicing those operations on Donaldjohanson reduced operational risk before the more distant Trojan encounters. [2][3]

Donaldjohanson was therefore more than a navigation checkpoint, even though it was not one of Lucy's primary science targets. Its bilobate form records collisions and reassembly in the asteroid belt. The observations let researchers test ideas about how small bodies evolve while also confirming that the spacecraft, instruments and ground team could execute a close flyby. [1][3]

After the April 2025 pass, Lucy continued through the main belt toward asteroids that share Jupiter's orbit around the Sun. Its first primary target is Eurybates in 2027. The Donaldjohanson flyby succeeded on both measures that mattered: it returned a close scientific dataset and demonstrated the encounter sequence Lucy will need for its main mission. [1][2][3]

Sources

  1. NASA — Asteroid Donaldjohanson overview
  2. NASA — Lucy completes Donaldjohanson flyby
  3. NASA — Lucy images asteroid Donaldjohanson

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