SCIENCE CHINA Physics, Mechanics & Astronomy • Article • March 2014 Vol.57 No.3: 569–576 doi: 10.1007/s11433-014-5399-z Geologic characteristics of the Chang’E-3 exploration region† ZHAO JianNan, HUANG Jun*, QIAO Le, XIAO ZhiYong, HUANG Qian, WANG Jiang, * HE Qi & XIAO Long Planetary Science Institute, China University of Geosciences, Wuhan 430074, China Received January 17, 2014; accepted January 18, 2014; published online January 22, 2014 We present topographic, geomorphologic and compositional characteristics of a 1°×1° (~660 km2) region centered near the landing site of Chang’E-3 using the highest spatial resolution data available. We analyze the topography and slope using Digi- tal Terrain Model (DTM) generated from Terrain Camera (TC) images. The exploration region is overall relatively flat and the elevation difference is less than 300 m, and the slopes of 80% area are less than 5°. Impact craters in the exploration region are classified into four types based on their degradation states. We investigate the wrinkle ridges visible in the exploration region in detail using TC and Lunar Reconnaissance Orbiter (LRO) Narrow Angle Camera (NAC) images. We calculate FeO and TiO2 abundances using Multispectral Imager (MI) data, and confirm two basaltic units: the northern part belongs to Imbrian low-Ti/very-low-Ti mare basalts, and the southern part is Eratosthenian low-Ti/high-Ti mare basalts. Finally, we produce a ge- ological map and propose the geologic evolution of the exploration region. We also suggest several rover traverses to explore interesting targets and maximize the potential scientific output. Cheng’E-3, Yutu rover, traverse planning, geological map, Mare Imbrium, the Moon PACS number(s): 96.20.Br, 96.20.Dt, 96.20.Ka, 96.30.Bc, 95.55.Pe Citation: Zhao J N, Huang J, Qiao L, et al. Geologic characteristics of the Chang’E-3 exploration region. Sci China-Phys Mech Astron, 2014, 57: 569576, doi: 10.1007/s11433-014-5399-z 1 Introduction is also taken into consideration, including impact craters, wrinkle ridges, and basaltic materials that have different ages. The CE-3 landing site and its nearby terrains have Nearly 40 years after the completion of the Apollo and Luna never been visited by any other missions. Therefore, the missions, the third Chinese lunar mission, Chang’E-3 exploration will shed light on the geologic characteristics, (CE-3), was launched on December 2, 2013 and safely geochemical diversity and evolution of Mare Imbrium. landed on the surface of the Moon on December 14, 2013. Geological maps in Apollo era [1] and recent studies The rover “Yutu” separated from the lander successfully [2–4] reveal regional geologic information for Sinus Iridum about 8 h later. The landing site of CE-3 is 340.49°E, and the adjacent terrains. However, the spatial resolution of 44.12°N, which is located in the northern part of Mare Im- previous maps is not sufficient for detailed geologic study brium (Figure 1). As the first Chinese lunar soft-lander and or for the rover traverse planning considering both scientific rover, the landing site is selected primarily considering en- and engineering requirements. Luckily, as unprecedented gineering constraints including topography, communication high spatial resolution remote sensing data being acquired and solar illumination. In addition, local geologic diversity by recent lunar missions (e.g., Chang’E 1 & 2, SELENE-1, Chandrayaan-1 and Lunar Reconnaissance Orbiter: LRO), *Corresponding author (HUANG Jun, email: [email protected]; XIAO Long, large scale geological mapping and detailed study are pos- email: [email protected]) †Contributed by XIAO Long (Associate Editor) sible for CE-3 landing site and its exploration region. In this © Science China Press and Springer-Verlag Berlin Heidelberg 2014 phys.scichina.com link.springer.com 570 Zhao J N, et al. Sci China-Phys Mech Astron March (2014) Vol. 57 No. 3 Figure 1 Location of CE-3 landing site (labeled by the star) within the Mare Imbrium. Background is LRO Wide Angle Camera image mosaic in a simple cylindrical projection. Figure 2 (Color online) TC Morning Map of the study area in a simple cylindrical projection (TCO_MAPm04_N45E339N42E342SC). The flag denotes the landing site of CE-3. “a–d” are craters of different degradation study, we mapped an area of 1°×1° (~660 km2) centered states. “e” is the largest crater in this area. “f & g” are chain craters. “h” is a crater that may have excavated materials of unit Im. “i” is the nearest near CE-3 landing site (Figure 2). We also presented topo- rayed crater from CE-3 landing site. “I” represents the broad gentle ridge graphic, geomorphologic, and elemental results of the ex- while “II” represents the narrow sharp ridges. Line “AB” is the profile line ploration region. The results will support the traverse plan- across the ridges. Dashed line is the boundary of unit Im and Em. “1 & 2” ning and assist Yutu rover to select interesting detecting are suggested traverse plans for the Yutu rover. targets. the south-southwest corner of Imbrium Basin. Hiesinger [8] also calculated the thickness of Eratosthenian lava flow 2 Geologic backgrounds ranging from 32 m to 50 m. Moore and Schaber [9] esti- mated the yield strength of lava flows in Mare Imbrium to The study area is located in the northern Mare Imbrium, be 100–200 Pa, the maximum average flow rate to be 5–14 about 140 km east to Sinus Iridum (Figure 1). Two named km/h and the density to be 3.0 g/cm3. Lucchitta [10] studied impact craters are in the adjacent regions: Laplace F, with a the morphology of wrinkle ridges in Mare Imbrium and diameter of 5.7 km, is 26 km away; and Laplace FA with suggested that the origin of the ridges maybe associate with diameter of 2.5 km and 1 km away from the landing site volcanic activity and faults. Xu et al. [11] proposed that the respectively. There are two main stratigraphic units in the concentric ridges in Mare Imbrium are controlled by the study area according to the geological map of the Sinus structure of the Imbrium basin and the north-south trending Iridum quadrangle compiled by Schaber [1], the unit in the ridges may result from the combination of basin structure north of the area is assigned as Im1 (Imbrian mare materials and regional stress field. 1) while the other unit in the middle and south is EIm (Era- tosthenian-Imbrian mare materials). However, subsequent age dating carried out by Hiesinger et al. [5], Bugiolacchi 3 Data & methods and Guest [6], and Qiao et al. [4] all confirmed that the unit Im1 is older than 3.2 Ga and the unit EIm is younger than 3.1 Topography 3.0 Ga. Therefore we renamed unit Im1 as Im (Imbrian mare materials) and EIm as Em (Eratosthenian mare mate- High spatial resolution topographic information is critical to rials). the rover traverse planning. The vertical measurement ac- Previous studies have made detailed analyses of geologic curacy of foot print of Lunar Orbiter Laser Altimeter features in Mare Imbrium such as lava flows and wrinkle (LOLA) onboard LRO can reach 0.1 m and the interval is ridges. Schaber [7] studied the characteristics of lava flows 25 m. Gridded data derived from LOLA has a spatial reso- in Mare Imbrium and proposed the thickness of Eratosthe- lution of 20 m along track and ~0.07° cross track [12]. nian phase-III lava flow is 10–65 m with an average of Haruyama et al. [13] produced global Digital Terrain Model 30–35 m. The eruptive source region was interpreted as in (DTM) using stereo pair images of Terrain Camera (TC) Zhao J N, et al. Sci China-Phys Mech Astron March (2014) Vol. 57 No. 3 571 onboard SELENE-1, and its spatial resolution is ~10 4 Results m/pixel. The TC topographic model has been compared to the laser altimeter data of SELENE-1 and the 1 difference 4.1 Topography is 3.2 m. In this study, we analyzed the topography of the CE-3 exploration region using TC DTM due to its better Surface topographic difference is less than 300 m for the spatial resolution than LOLA gridded data at ~44°N. We whole study area (Figure 3). The middle and southern parts also calculated the surface slope in a 3×3 analysis windows are higher in elevation, while the northwest and northeast using difference computation with TC DTM. are lower. The lowest point in the study area is 2850 m, located within an impact crater of northwest, and the highest 3.2 Geomorphology analysis point is located in the south (2560 m). The lander is locat- ed on the continuous impact ejecta deposits of a small crater, We use images obtained from the Wide Angle Camera and the local elevation is about2610 m. (WAC) and Narrow Angle Camera (NAC) of LRO and TC According to the slope map derived from the TC DTM of SELENE-1 to study the geomorphology. The spatial res- (Figure 4), 80% of the study area is relatively flat (less than olution of WAC images is 100 m/pixel [14]. The mosaic of 5°). The terrain slopes near impact craters are larger, and the WAC images shows albedo differences and serves as back- steepest part is inner walls of impact craters (more than 20°). ground. NAC images have a spatial resolution of 0.5 The landing site of CE-3 is about 5°, which is suitable for m/pixel, and we use them to study the small scale geologic features in detail. TC images have different illumination conditions, and moderate spatial resolution (10 m/pixel) [15].