New geological maps of the Apollo landing sites

NEW GEOLOGICAL MAPS OF THE APOLLO LANDING SITES. W. Iqbal1, H. Hiesinger1, C. H. van der Bogert1, D. Borisov1, and T. Gebbing1, 1Institut für Planetologie, Westfälische Wilhelms-Universität, Wilhelm-Klemm-Str. 10, 48149, Münster, Germany, [email protected]. Introduction: Historical data from the Apollo program improved knowledge of lunar geology tremendously in many aspects. Nevertheless, the geological maps that were completed before the missions can and should now be updated with new data [1-6] and revisited with knowledge regarding geological processes that has been gained in the ~50 years since the mission [e.g., 7]. As part of a large project, we are using recent lunar datasets to produce comprehensive geological maps around the Apollo landing sites. These new maps are being used to test the calibration [8] of the lunar cratering chronology [9,10] by pinpointing the sampling sites of the collected samples [11] and reevaluating their position within and relevance for lunar stratigraphy. The maps can also be used for planning future missions [e.g., 12]. Methods: Detailed mapping is achieved using data with different spatial resolutions. Albedo differences are mapped using images from the Lunar Reconnaissance Orbiter (LRO) Wide Angle (WAC; 100 m/pixel) and Narrow Angle (NAC; ~0.5-1.2 m/pixel) cameras [1], as well as Selene/Kaguya Terrain Camera image mosaics. We use various digital elevation models (DEM) to map structures with topographic differences. These DEMs include the LRO WACderived (100 m/pixel) [2], LOLA (100 m/pixel), and LOLA/Kaguya merged (60 m/pixel) [3] DEMs. Geological units are also mapped on the basis of spectral differences in Clementine [4], Chandrayann-1 Moon Mineralogy Mapper (M3) [5], and Kaguya Multiband Imager (MI) data [6]. The stratigraphic system of Wilhelms (1987) [7] is adapted in our new geological maps. The symbology used for geological units follows the standards of the Federal Geographic Data Committee (2006) [13] and harmonized with the PlanMap mapping standards, and the nomenclature is adapted from the Gazetteer of Planetary Nomenclature (1999) [14]. Geological units: The highlands contain units such as IpIt-Imbrian pre-Imbrian terrains (which are Nectarian terrains covered or mixed with the Imbrian materials), Fra Mauro Formation Imbrium basin ejecta units (Ifm-Imbrian Fra Mauro formation and Ifs-Imbrian Fra Mauro smooth plains), and IpImbrian plains. Mare units are mapped on the basis of spectral differences [e.g., 4-6] using the same approach as [15], thus the contacts between the mare units are mapped as approximate spectral boundaries. In a few places, the stratigraphy of the mare units was identified through crater densities derived from crater size-frequency distribution (CSFD) measurements [e.g., 16-18]. The different generations of craters are mapped as Cc-Copernican craters, EcEratosthenian craters, Ic-Imbrian craters, and NcNectarian craters or pIc-preImbrian craters. Implications: The lunar cratering chronology is based on CSFD measurements that are calibrated with the radioisotopic and exposure ages of the lunar Figure 1. The detailed geological maps of the Apollo 11[16], 12 [17], and 14 landing sites [19]. (a) The Apollo 11 landing site lies in southwestern Mare Tranquillitatis. (b) The Apollo 12 landing site lies south of Copernicus crater in Oceanus Procellarum. (c) Preliminary geological map of the Apollo 14 landing site on the Fra Mauro formation (Ifm), east of the Apollo 12 landing site. Locations of the landing modules are marked by green triangles. samples [9,10]. It is used to derive absolute model ages (AMAs) of unsampled geological units across the Moon, as well as on planetary bodies throughout the Solar System [e.g., 15]. On the basis of our new geological maps [16-21], we defined and refined homogeneous geological counting areas for measuring CSFDs and deriving accurate N(1) reference values and AMAs, which are necessary to test and improve the lunar cratering chronology [9]. In addition, the new geological maps can be used to examine and understand potential landing sites for technology demonstration missions. For example, van der Bogert (2020) [12] used our detail geological map [18] in an analysis of landing sites for an end-toend in situ resource utilization demonstrator mission concept for ESA. The new geological maps provide new and refined perspectives on the locations and relationships between the Apollo samples and remotely-sensed compositional and morphological differences. Our geological maps can be used to investigate the exact origin of the collected samples [e.g., 11] and further enhance our knowledge about the history of the geological processes that took place on the Moon. Acknowledgements: WI and HH were funded by the German Research Foundation (Deutsche Forschungsgemeinschaft SFB-TRR170, subproject A2) and CvdB was supported by EU H2020 project #776276, PLANMAP. References: [1] Robinson et al (2010) Space Sci. Rev. 150, 81-124. [2] Scholten, et al. (2012). JGR. 117, E00H17. [3] Barker et al. (2016) Icarus 273, 346-355. [4] Pieters et al. (1994) Science 266, 1844-1848. [5] Isaacsom, et al. (2013). JGR Planets. 118, 369-381. [6] Ohtake, et al (2013) Icarus 226, 364-374. [7] Jolliff, et al. (2006) New Views of the Moon 60 [8] Hiesinger et al. (2020) LPSC 51, 2045. [9] Neukum, (1983) Habil. thesis, U. of Munich. [10] Neukum, et al. (2001) Space Sci. Reviews 96, 55-86. [11] Haber, et al (2018) AGU, P31G3785. [12] van der Bogert, et al. (2020) LPSC 51, #1876. [13] FGDC (2006). FGDC-STD-013-2016. [14] Blue, J. (1999) Gazette. of Planet. Nomen. USGS. [15] Hiesinger, et al. (2000) JGR 105, 29239-29275. [16] Iqbal, et al (2019) Icarus 333, 528-547. [17] Iqbal, et al (2018) LPSC 49, 1002. [18] Iqbal, et al (2019) LPSC 50, 1005. [19] Borisov, et al (2019) LPSC 50, 2323. [20] Gebbing, et al (2019) LPSC 50, 2337. [21] Iqbal, et al (2018) LPSC 51, 1073. Figure 2. Preliminary new geological maps of the Apollo landing sites 15 [21], 16 [20], and 17 [18]. (a) The Apollo 15 landing site lies at the eastern rim of the Imbrian Basin. (a’) Inset shows a local geological map around the Apollo 15 landing site. (b) Map around the Apollo 16 landing site. (c) The Apollo 17 landing site near the eastern rim of the Serenitatis basin. (c’) The local geological map of the Taurus Littrow valley around the Apollo 17 landing site. The green triangles show the locations of the landing sites.