Evidence for the Presence of Thin and Heterogenous Dust Deposits on Ryugu's Boulders From Hayabusa2 MARA and Sample Data

Hamm, M.; Hamilton, V. E.; Goodrich, C. A.

doi:10.1029/2023gl104795

Cited by 1 publication

(1 citation statement)

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“…This rock was found to have a thermal inertia (∼250-280 J m −2 K −1 s −1/2 ; Grott et al 2019;Hamm et al 2022) that is very similar to values obtained from orbit (Sugita et al 2019;Shimaki et al 2020) and somewhat higher than the tagged rock. The presence of all but a very small amount of dust (3% spatial coverage) was ruled out by thermal models (Grott et al 2019;Hamm et al 2023). Rather, similar to Bennu's low-reflectance boulders, the thermal inertia of Ryugu's boulders has been attributed to an internal porosity of 30%-52% (Grott et al 2019;Hamm et al 2020)-potentially much higher than any measured meteorite analog (Flynn et al 2018;Opeil et al 2020), which could be indicative of low strength and high friability.…”

Section: Discussionmentioning

confidence: 96%

Rocks with Extremely Low Thermal Inertia at the OSIRIS-REx Sample Site on Asteroid Bennu

Ryan,

Rozitis,

Pino Munoz

et al. 2024

Planet. Sci. J.

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The Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer (OSIRIS-REx) mission recently returned a sample of rocks and dust collected from asteroid Bennu. We analyzed the highest-resolution thermal data obtained by the OSIRIS-REx Thermal Emission Spectrometer (OTES) to gain insight into the thermal and physical properties of the sampling site, including rocks that may have been sampled, and the immediately surrounding Hokioi Crater. After correcting the pointing of the OTES data sets, we find that OTES fortuitously observed two dark rocks moments before they were contacted by the spacecraft. We derived thermal inertias of 100–150 (±50) J m−2 K−1 s−1/2 for these two rocks—exceptionally low even compared with other previously analyzed dark rocks on Bennu (180–250 J m−2 K−1 s−1/2). Our simulations indicate that monolayer coatings of sand- to pebble-sized particles, as observed on one of these rocks, could significantly reduce the apparent thermal inertia and largely mask the properties of the substrate. However, the other low-thermal-inertia rock that was contacted is not obviously covered in particles. Moreover, this rock appears to have been partially crushed, and thus potentially sampled, by the spacecraft. We conclude that this rock may be highly fractured and that it should be sought in the returned sample to better understand its origin in Bennu’s parent body and the relationship between its thermal and physical properties.

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