1,2,3,2,- 1SwRI, Depart of Space Sciences, Boulder, United States of America (hal@boulder.swri.edu)
- 2SwRI, Depart of Space Sciences, Boulder, United States of America
- 3NASA Goddard Spaceflight Center, Greenbelt, United States of America
- 4NASA Headquaters, Washington, United States of America
- *A full list of authors appears at the end of the abstract
On April 20, 2025 NASA's <i>Lucy</i> mission performed a flyby of the main belt asteroid (52246) Donaldjohanson, hereafter DJ. <i>Lucy</i> is a NASA Discovery-class mission to study primitive bodies near both the L<sub>4</sub> and L<sub>5</sub> Lagrange points with Jupiter - the Jupiter Trojans [1]. The flyby of DJ was intended as a full-scale end-to-end test of <i>Lucy</i>'s systems before its first Trojan encounter in 2027. The spacecraft and ground systems performed flawlessly.
DJ is a C-type asteroid [2] with a semi-major axis of 2.4 au. From the ground, it is observed to have a high-amplitude lightcurve with a rotation period of ~250 hr [3]. It is a member of the Erigone asteroid family, which an age estimated to be only 155 Myr [4]. <i>Lucy</i> approached DJ from a phase angle of 14 deg and with a relative velocity of 13.4 km/sec [1]. Its close approach distance was about 960 km.
<i>Lucy</i> determined that DJ is an elongated bi-lobed object about 8 km long with an axis ratio greater than 2 to 1. It has a well-defined neck between the two lobes that shows evidence of significant geological processing. One lobe appears to be significantly larger than the other. <i>Lucy</i> obtained useful scientific data from all of its instruments: L'LORRI, a high-resolution panchromatic camera [5], TTCam (a wide-field panchromatic camera [6]), L'Ralph/MVIC (a five color color camera [7]), L'Ralph/LEISA (a near-infrared spectroscopic mapper [7]), and L'TES (a thermal IR spectrometer [8]). The results will be summarized here. More details will be given in subsequent presentations in this session.
[1] Levison et al. (2025), PSJ, 2:171, doi:10.3847/PSJ/abf840.
[2] Souza-Feliciano et al. (2020), Icarus, 338, 113463.
[3] Ferrais et al. (2021), AAS/DPS meeting #53, id.306.19.
[4] Marchi et al. (2025), PSJ, 6:59, doi:10.3847/PSJ/adb4f4.
[5] Weaver et al. (2023), SSRv, 209, doi:10.1007/s11214-023-01028-z.
[6] Bell et al. (2023), SSRv, 219, doi:10.1007/s11214-023-01030-5.
[7] Reuter et al. (2023), 219, doi:10.1007/s11214-023-01009-2.
[8] Christensen et al. (2024), SSRv, 220. doi:10.1007/s11214-023-01029-y.
Levison et al.
How to cite: Levison, H., Marchi, S., Noll, K., Spencer, J., and Statler, T. and the The Lucy Team: The Lucy Encounter with asteroid (52246) Donaldjohanson - An Overview, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–12 Sep 2025, EPSC-DPS2025-408, https://doi.org/10.5194/epsc-dps2025-408, 2025.
