Potential landing sites for the Chang'e-4 exploration mission to the Apollo Basin, Moon

POTENTIAL LANDING SITES FOR THE CHANG’E-4 EXPLORATION MISSION TO THE APOLLO BASIN, MOON. C. Orgel1 (o[email protected]), M. A. Ivanov2, H. Hiesinger3, J.-H. Pasckert3, C. H. van der Bogert3, G. Michael1. 1 Freie Universität Berlin, Department of Planetary Sciences, 12249 Berlin, Malteserstrasse 74-100, Germany, 2Vernadsky Inst., RAS, Russia, 3Westfälische Wilhelms-Universität, Münster, Germany. Introduction: As the oldest and deepest impact structure on the Moon, the South Pole-Aitken Basin (SPA) on the lunar farside is a scientifically high priority site for human and robotic exploration [1]. The lunar farside has not been visited by any exploration missions so far, but it is the focus for Chang’e-4 robotic missions planned for the end of 2018 [2]. The Chang’e-4 mission aims to deploy a relay satellite into Halo-orbit around EM-L2 and land with a Yutu heritage rover on the lunar surface. The provisional scientific objectives of Chang’e-4 [2] are to study: (1) the interaction between the solar wind and lunar surface, (2) the formation mechanism of lunar regolith and dust, (3) the lunar-based VLF astronomical potential, (4) the regional geochemistry and subsurface, and (5) the recent impact flux of the Moon. The most likely landing site for the Chang’e-4 robotic mission will be the 538 km-diameter Apollo basin in the NE quadrant of the SPA basin. Here, we provide a detailed analysis of three high-priority (Fig. 1 regions of interest (ROIs) with example rover traverses of 2.5 km, 5 km and 10 km radius from the center of ROIs in the central and southern mare deposits of the Apollo basin. The proposed high-priority ROIs have high scientific interest based on prioritized science concepts defined in the 2007 National Research Council (NRC) report [1] and the scientific objectives of the mission. Science rationale: The Apollo basin has been mapped as pre-Nectarian [3-5], preNectarian/Nectarian [6], and Nectarian [7]. According to CSFD measurements, its absolute model age (AMA) is 3.91 Ga [5] to 4.14 Ga [7]. Thus, the Apollo basin is one of the youngest basins inside the SPA basin. Based on GRAIL data, the crustal thickness is less than 5 km beneath the Apollo basin [8]. The NE-E rim of the Apollo basin exposes anorthositic material from the highlands along the SPA rim and possibly impact melt and/or mantle material from the SPA interior [9]. The basin floor is mainly covered by four mare basalt provinces (center, south, west, and east), their AMAs ranging from 2.30 to 3.45 Ga [10]. The mare deposits have enhanced FeO and TiO2 abundances compared to the immediate surroundings [11]. Data and Methods: To evaluate the potential science return of each proposed ROI, we use all available datasets from previous lunar missions and studies [11]. The terrain trafficability is determined via slope maps, and digital elevation models derived from the LOLA instrument, at resolutions of 60 m/pix. The terrains that compose the Apollo basin are visualized using LRO WAC mosaics of 100 m/pix, and individual NAC images of 1 m/pix, and Kaguya Terrain Camera images of 7 m/pix. We use the Kaguya images as the photobase for geologic mapping and counting craters >50m for crater size-frequency distribution analyses. Geologic maps at 1:50,000 scale are being compiled for the central and southern portions of the Apollo basin, as well as a detailed regional geologic map of the northern portion of SPA [12]. FeO and TiO2 contents are determined using Clementine 100 m/pix global maps [13], as well as Kaguya LISM 80/pix data [14]. Selection of ROIs: The central and southern mare deposits were the main objectives of high-priority ROIs. These areas are smooth with <5° slopes and have low crater densities. The selected ROIs reflect a geologically complex area (Fig. 1), where both mare deposits are covered by younger, Copernican-aged ejecta material of various thickness and distribution, and “pure” mare is also accessible. In addition, the mare deposit has high in situ resource utilization (ISRU) potential due to relatively high FeO and TiO2 contents ranging from 14-20 and 1-7 wt%, respectively (Tab. 1). In contrast, the younger ejecta materials have low FeO and TiO2 contents representing material beneath the mare deposit. The origin of that material could be SPA and/or Apollo impact melt, which is a high-ranking scientific objective [1]. ROI 1 ROI 2 ROI 3 FeO TiO2 FeO TiO2 FeO TiO2 Min. 16.15 0.80 17.65 3.95 17.39 5.71 Max. 18.58 7.50 18.80 8.73 18.58 9.91 Average 17.90 4.20 18.33 6.78 18.18 7.53 Table 1: FeO and TiO2 content of mare deposits in the ROIs based on 50 random samples within the ellipses. Conclusion: These high-priority areas could fulfill the general engineering constraints and the scientific objectives, as well as ISRU potential of the mission. In situ observations and sample analyses can help address six of seven NRC concepts (1-3, 5-7) and provide a high ISRU potential at all selected ROIs. Acknowledgement: This work was funded by the Deutsche Forschungsgemein-schaft (SFB-TRR 170, subproject A3-2) and Russian Science Foundation (grant 17-17-01149) to MAI. References: [1] NRC (2007) National Academies Press. [2] Wang Q. and Liu J. (2016) Acta Astronautica 127, 678-683. [3] StuartAlexander (1978) No. I-1047. [4] Wilhelms et al. (1979) No. I-1162. [5] Hiesinger et al. (2012) LPSC #2863. [6] Fassett et al. (2012) JGR 117: E00H06. [7] Orgel et al. (2018) LPSC #1395. [8] Wieczorek et al. (2013) Science 339, 671-675. [9] Morrison D. A. and Bussy D. B. J. (2007) LPSC #1501. [10] Pasckert et al. (2018) Icarus 299, 538562. [11] Kring D.A. and Durda D.D. (2012) LPI Contrib. 1964. [12] Ivanov et al. (2018) LPSC 1138. [13] Lucey et al. (2000) JGR 105, 20,297-20,306. [14] Lemelin et al. (2016) LPSC #2994. Figure 1: High-priority Region of Interests (ROI) in the Apollo basin. A/Slope map derived from LOLA and TC 60 m/pix data. White boxes indicate the location of geologic maps. B-D/Geologic maps of the central and south Apollo basin. C-E/ FeO maps derived from Clementine 100 m/pix data. High-priority ROIs indicated with example rover traverses (circles) of 2.5 km (yellow), 5 km (white) and 10 km (red) radius from the center of ROIs