Thermal-IR Observations of (152830) Dinkinesh during the Lucy Mission FlybyOPEN ACCESS
Samuel L. Jackson, Joshua P. Emery, Benjamin Rozitis, Philip R. Christensen, John R. Spencer, Stefano Mottola, Victoria E. Hamilton, Carly J. A. Howett, Simone Marchi, Keith S. Noll
The Planetary Science Journal, Volume 6, Number 7, Published 2025 July 17
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“NASA’s Lucy spacecraft flew by the main-belt asteroid (152830) Dinkinesh on 2023 November 1, providing a test of its instruments and systems prior to its encounters with the Jupiter Trojans and enabling an opportunity for scientific investigation of this asteroid. Analysis of disk-integrated radiance spectra of Dinkinesh collected by the Lucy Thermal Emission Spectrometer (L’TES) instrument during the close approach reveals a thermal inertia for Dinkinesh of 91 ± 24 J m−2 K−1 s−1/2 and a surface roughness of 35° ± 7° rms slope. These values for the thermal inertia and surface roughness are comparable to values derived for other small S-type asteroids such as (65803) Didymos. The Dinkinesh flyby also provided the opportunity to develop new techniques for extracting data when the target body does not fill the field of view of the L’TES instrument, which proved challenging for predecessors of this instrument such as OTES on OSIRIS-REx. The grain size of the regolith of Dinkinesh, estimated to be r =1.2 -0.6/+ 0.9 mm, is below expected trends with size but is comparable to that of similarly sized asteroids that are either binaries or may have undergone rotational fission in the past. These findings imply that fine-grained materials are being preferentially retained on the primaries of multiple systems, either by cohesive forces or by redeposition after impact events on the secondaries.”
Animated content (excerpt):
Figure 8. Demonstration of a high phase angle geometry on approach to Dinkinesh where the unlit side (and therefore the side with a lower-quality shape model) comprises a significant proportion of the area of Dinkinesh visible to the L’TES instrument. The unlit side, however, is cooler and therefore contributes less flux to the total received at the detector. The left image shows simulated illumination, mapped onto the downsampled shape model of Dinkinesh discussed earlier. The right image shows the simulated temperature distribution, similarly mapped onto the downsampled shape model. The title in the image indicates where the times correspond to the period of one of our 10 average spectra. An animated version of this figure shows the simulated geometries of the full encounter. The animation shows how the relative geometry of Dinkinesh would have looked from the Lucy spacecraft as the encounter progressed. The speed of the animation decreases from 60× real-time speed to 15× real-time speed during the period covering the analyzed L’TES spectra.
