Lucy Snaps 5‑Mile‑Long Donaldjohanson at 30,000 mph from 600 Miles—What Its Neck Reveals

Govind Tekale

Launched from Cape Canaveral on October 16, 2021, Lucy was placed on a trajectory to explore Jupiter’s Trojan asteroids.

Representative Image. Photo Credits: Lucy Mission Prelaunch Q202110140003)

A dress rehearsal for Trojan encounters was conducted on April 20, 2025, when Lucy was flown past (52246) Donaldjohanson at 960 km.

Representative Image. Photo Credits: Tadias Magazine (CC BY 2.0)

Donaldjohanson was revealed to be a C‑type contact binary measuring approximately 8 km × 3.5 km, linked by a narrow neck.

Representative Image. Photo Credits: ESO. Acknowledgement: JAXA (CC BY 4.0)

The asteroid was traced to the Erigone collisional family, formed about 150 million years ago by a catastrophic breakup.

Representative Image. Photo Credits: NASA (PDM 1.0)

An exceptionally slow rotation period of about 252 hours was confirmed by photometric observations.

Representative Image. Photo Source: CTIO/NOIRLab/NSF/AURA (CC BY 4.0)

L’LORRI was used to capture surface details down to 50–70 m from 660–1 000 km away, showcasing its high-resolution imaging

Representative Image. Photo Source: Illustration of Asteroid (CC BY 4.0)

L’TES was employed to measure the asteroid’s thermal inertia, enabling inferences about regolith grain size.

Representative Image. Photo Source: NASA

Data from the flyby were downlinked over the following week, with preliminary images available within 24 hours.

Representative Image. Photo Source: NASA's Marshall Space Flight Center (CC BY-NC 2.0)

Comparisons to Bennu, Ryugu and Arrokoth were prompted by the contact‑binary morphology and carbonaceous composition.

Representative Image. Photo Source: ESO/M. Kornmesser/Marchis et al.(CC BY 4.0)

Eurybates will be encountered in August 2027, marking the start of Lucy’s primary Trojan campaign.

Representative Image. Photo Source: Stefano Mottola et al (CC BY 4.0)

Polymele, Leucus and Orus will follow, extending the mission through to 2029 before a return for gravitational assists

Representative Image. Photo Source: NOIRLab/NSF/AURA/J (CC BY 4.0)

Instrument sequences were refined during the Donaldjohanson flyby to optimize performance for more distant targets.

Representative Image. Photo Source: NASA Orion Spacecraft (CC BY-NC-ND 2.0)

Science teams at NASA Goddard, SwRI and DLR were mobilized immediately to analyze the new Donaldjohanson data.

Representative Image. Photo Source: NASA's James Webb Space Telescope (CC BY 2.0)

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