¹Huacheng Li,^2,6Zongyu Yue,²Yangting Lin,^3,6Kaichang Di,^1,4Nan Zhang,^5,6Jianzhong Liu
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2022.115333]
¹Key Laboratory of Orogenic Belts and Crustal Evolution, School of Earth and Space Sciences, Peking University, Beijing 100871, China
²Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
³State Key Laboratory of Remote Sensing Science, Aerospace Information Research Institute, Chinese Academy of Sciences, Beijing 100101, China
⁴Earth Dynamics Group, School of Earth and Planetary Sciences, Curtin University, Perth, Australia
⁵Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China
⁶CAS Center for Excellence in Comparative Planetology, Hefei 230026, China
Copyright Elsevier

Mineral olivine and Mg-rich spinel observed in Das crater were previously attributed to the excavation from the lunar lower crust or even mantle. To test this hypothesis, we developed a three-dimensional hydrocode SALEc to simulate the formation of such an elliptical crater. The hydrocode SALEc was examined and verified by comparing its results with experimental data and another code iSALE-2D. Based on the comparison between our SALEc’s numerical results and observations, we found that Das crater can be formed by an impact with the projectile of 6.0 km in diameter, impact velocity of 10 km/s, and impact angle of 70° relative to the vertical. In the impact, the excavation depth of Das crater is ~3.0 km, much less than the lunar crust thickness, hence the mineral olivine and Mg-rich spinel observed in this crater is unlikely originated from lunar lower crust or mantle. Numerical simulation results also show that some projectile materials can survive in this impact and are distributed in the downrange crater floor. Given the abundant olivine in many asteroids, we propose that olivine observed in Das crater is most probably originated from projectile remnants instead of excavation from the depth.

¹Aleksandra N. Stojic et al. (>10)
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2022.115344]
¹Institut für Planetologie, Westfälische Wilhelms-Universität Münster, Wilhelm – Klemm Str. 10, 48149 Münster, Germany
Copyright Elsevier

The effect of surface regolith gardening and melt layer production produced by space weathering (SW) (owing to micrometeorite [according to comment rev#1] bombardment) of surficial regolith layers of airless planetary surfaces was investigated in an experimental setup by using laser-induced ablation of powdered analog material (synthetic Fo100) under vacuum with a ns-pulsed infrared laser. The investigated analog pellets were prepared from the fine fraction (< 1 μm) up to a grain size of 280 μm, which resembles the uppermost regolith surface of many airless planetary bodies. The Fo-powder was pressed into shape to form a pellet. We focused here on nanometer-sized structural modifications that are induced in the relocated grains, sputtered off ejecta material and melt sprinkles that formed away from the craters caused by laser irradiation of the pressed pellet surface. The ejecta particles were redistributed over the entire pellet surface and beyond. The forming sputter film, melt sprinkles and ballistically ejected grains were caught on carbon film grids positioned nearby the craters. The grids were investigated with a transmission electron microscope (TEM) to discern between the distinct deposition types that were formed by ejecta condensate and partially molten ejected nanometer-size analog grains. Apart from a heavily modified pellet surface, we found that deposited droplets are mostly amorphous with minor nanocrystalline subdomains. Eight out of ten droplets show distinct incipient crystallization stages. This indicates at a relatively high amount of amorphous regolith material at the incipient stage of SW for airless bodies, if the regolith is altered via micrometeorite bombardment.