Ejecta From the Orientale Basin at the Chang'E‐4 Landing Site

Abstract

Radargrams obtained by the Yutu‐2 rover reveal that the post‐mare deposits at the Chang'E‐4 landing site are ∼45 m thick, consistent with estimations based on orbital observations. Besides obvious ejecta from Finsen, polarized interpretations exist on whether or not the Alder crater is another contributor to the post‐mare deposits, although predicted thicknesses of ejecta from all potential source craters are not adequately large compared to observations. We recognize that the rover has been exploring along a shared crater wall of two secondaries from Finsen. Mechanics of secondary impacts suggests that the discontinuous layers of coarse and fine materials observed in the radargram are older than Finsen. Cross‐cutting relationships and crater density comparisons show that Alder is older than the mare basalts, and the Orientale basin was the major source for the post‐mare materials. Lower‐crust materials excavated by Orientale constituted a substantial portion of the surface regolith detected by the rover.

A Novel Approach for Permittivity Estimation of Lunar Regolith Using the Lunar Penetrating Radar Onboard Chang’E-4 Rover

“…The CE-4 landing site is located on the ejecta ray of the Finsen crater, which contributes an ejecta deposit of ~7 m calculated by the model proposed by Pike et al [33]. The thickness of the lunar regolith is estimated to be ~12 m by the LPR, which is thicker than that of the CE-3 landing site [2,[34][35][36]. The loss tangent of lunar materials is estimated to be ~0.005, which is close to that of typical lunar regolith [2,35].…”

Inferring the Shallow Layered Structure at the Chang’E‐4 Landing Site: A Novel Interpretation Approach Using Lunar Penetrating Radar

“…Geological context suggests that the craters VK L, L', Finsen and Orientale have contributed to most of the post-Imbrian ejecta layers of the VK crater (Paskert et al, 2018;Huang et al, 2018;Di et al, 2019;Xiao et al, 2021). The thickness of the Finsen ejecta at the area of the Chang'E-4 landing site is estimated -via numerical simulations (Di et al, 2019)-at ∼ 30 meters.…”

Rock Fragments in Shallow Lunar Regolith: Constraints by the Lunar Penetrating Radar Onboard the Chang'E‐4 Mission

“…Featuring a model age of ∼3.63.7 Ga (J. Huang, Xiao, et al., 2018; Ling et al., 2019), the landing area is covered by a thick and mature regolith that is ∼12 m thick. The lunar penetrating radar (i.e., LPR) onboard the Chang'E‐4 rover (Yutu‐2) has been scanning the interior structure of the subsurface (C. Li et al., 2020; Xiao et al., 2021). The high‐frequency channel of the LPR is capable of revealing subsurface materials with a resolution of ∼0.3 m in typical regolith (Su et al., 2014).…”

“…The high‐frequency channel of the LPR is capable of revealing subsurface materials with a resolution of ∼0.3 m in typical regolith (Su et al., 2014). Based on hyperbolic echo patterns revealed in the radargram, dozens of competent rocks have been discovered in this regolith layer (Lai et al., 2019; C. Li et al., 2020; Xiao et al., 2021), which are much fewer than those in the regolith‐like ejecta deposits at the Chang'E‐3 landing site (Ding, Cai, et al., 2020; Fa et al., 2015). However, no subsurface boulders shallower than ∼2 m have been detected in the regolith (Xiao et al., 2021).…”

“…Based on hyperbolic echo patterns revealed in the radargram, dozens of competent rocks have been discovered in this regolith layer (Lai et al., 2019; C. Li et al., 2020; Xiao et al., 2021), which are much fewer than those in the regolith‐like ejecta deposits at the Chang'E‐3 landing site (Ding, Cai, et al., 2020; Fa et al., 2015). However, no subsurface boulders shallower than ∼2 m have been detected in the regolith (Xiao et al., 2021). The top ∼1 m of the regolith was revealed to be free of fragments that are larger than 1 cm, except for the limited occurrence of regolith clumps that were excavated by fresh and small impact craters (Ding, Xiao, et al., 2020; Gou et al., 2021; Lin et al., 2020).…”