The Lucy flyby of (52246) Donaldjohanson: A bilobed asteroid with tumbling rotation.

Marchi, Simone; Levison, Harold F; Noll, Keith S; Spencer, John R; Statler, Thomas S; Barnouin, Olivier S; Bell, James F; Bierhaus, Edward B et al. · Science · 2026

basic_science · Level V

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Abstract

The main belt asteroid (52246) Donaldjohanson (DJ) is a likely member of the Erigone asteroid family. This implies that DJ is a fragment of a larger parent body that was destroyed in a collision about 155 million years ago. We report observations taken during a flyby of DJ by the Lucy spacecraft. We found that DJ is composed of two heavily cratered lobes, connected by a smoother neck, with overall dimensions 8.8 kilometers (km) by 4.4 km by 3.1 km. The crater density is consistent with the Erigone family's age, except for craters <0.4 km, which have been preferentially erased. DJ rotates slowly in a tumbling state, likely owing to spin-down by radiative forces. Surface spectra show iron-bearing phyllosilicates, indicating moderate aqueous evolution on the parent body.