(52246) Donaldjohanson and the Architecture of Bilobed Small Bodies

Kurzfassung

The Lucy spacecraft flew by the Main Belt asteroid (52246) Donaldjohanson, hereafter DJ, on April 20, 2025. Images obtained during the flyby show DJ to be an elongated object, about 8 km long with an axis ratio greater than 2 to 1, consisting of two distinct lobes connected by a narrow neck. A detailed shape model [1] will be required to further quantify this structure.Similarly shaped small bodies have been directly observed among Near Earth Objects [2-4], the Main Belt [5], comets [6-9] and in the Kuiper Belt [10]. Many more elongated/bilobed objects can be inferred from lightcurve observations [11]. DJ is a potentially valuable addition to understanding these objects because it resides in the Main Belt and is part of a collisional family of known age [12].We compile estimated lobe dimensions and apparent orientations in a variety of small bodies of similar size to DJ and discuss observable trends. We compare results to expected behavior in collisional systems and accretion models [13-18].Acknowledgement: The Lucy mission is funded through the NASA Discovery program on contract No. NNM16AA08CReferences: [1] Mottola et al., this meeting, [2] Fujiwara et al., Science, 312, 5778, 1330-1334, 2006. [3] Hu, Acta Astro. Sinica, 60, 5, 46, 2019. [4] Benner et al. in Asteroids IV, 2015, pp. 165-182. [5] Levison et al. Nature, 629, 8014, 1015-1020, 2024. [6] Keller et al., A&Ap, 187, 807-823, 1987. [7] Boice et al., EM&P, 89, 301-324, 2002. [8] A'Hearn et al., Science, 332, 1396, 2011. [9] Sierks et al., Science 347, 6220, 2015. [10] [1]Stern et al. PSJ 4, 9, 176, 2023. [11] Cannon, MNRAS 538, 4, 2311-2329, 2025. [12] Marchi et al., PSJ 6, 3, 59, 2025. [13] Schwartz et al., Nature Astronomy 2, 379-382, 2018. [14] Jutzi and Benz, A&Ap 597, A62, 2017. [15] Jutzi, P&SS 177, 104695, 2019. [16] Jutzi and Asphaug, Science 348, 6241, 1355-1358, 2015. [17] Hirabayashi and Scheeres, Icarus 317, 354-364, 2019. [18] Scheeres, Icarus 436, 116563, 2025.