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The Lucy Encounter with (152830) Dinkinesh

Presentation #102.06 in the session Asteroids: Objects of Interest (Oral Presentation)

Published onOct 23, 2023
The Lucy Encounter with (152830) Dinkinesh

The Lucy mission, launched in October 2021, is designed to conduct the first reconnaissance of the Trojan asteroids, by means of a series of flybys of 5 Trojan systems (Eurybates, Polymele, Leucus, Orus, and Patroclus) between 2027 and 2033. In addition, the mission plan has always included a flyby of a main-belt asteroid, 52246 Donaldjohanson, in April 2025, as a rehearsal for the Trojan encounters. In August 2022, a search for smaller potential targets found that the Lucy trajectory would pass a second main-belt asteroid, (152830) Dinkinesh, at a range only 64,000 km, on November 1st 2023. In early 2023, the Lucy project decided to spend the few m/sec of delta-V necessary to enable a close (425 km) flyby of Dinkinesh on that date. The flyby is primarily intended as a test of Lucy’s closed-loop target tracking system, and pointing stability, during close asteroid encounters, providing information 18 months earlier, and with a more Trojan-like flyby geometry, than the Donaldjohanson flyby. Obtaining science data is much lower priority, and the planned observing sequence is much simpler than planned for Lucy’s primary targets. However, unique science will nonetheless be obtained if the encounter, and particularly the closed-loop target tracking, is fully successful.

Dinkinesh is an inner-belt S-type asteroid (de León et al. (2023), arXiv:2303.05918v1, DOI: 10.1051/0004-6361/202346278; Bolin et al. (2023), arXiv:2303.08130, DOI: 10.1016/j.icarus.2023.115562), with absolute magnitude HR = 17.17 and rotation period 52.7 hours (Mottola et al. (2023), DOI: 10.1093/mnrasl/slad066). A likely albedo of 0.20 yields a diameter of ~1.0 km. If successful, the planned flyby sequence will yield science data with the following resolutions, expressed as the number of pixels across Dinkinesh’s assumed 1-km diameter: panchromatic images (L’LORRI camera): 460 pixels; color images (L’Ralph MVIC camera): 70 pixels; NIR image cubes (L’Ralph LEISA NIR spectrometer): 36 pixels; as well as disk-integrated thermal emission measurements from the L’TES instrument. The result will be a unique portrait of the smallest main-belt asteroid yet encountered by a spacecraft, comparable in size to NEOs such as Bennu and Ryugu, whose surfaces are very different from those of larger explored asteroids.

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