Comparative Study of Moretus and Tycho Craters: Insight into Crater Degradation Processes

COMPARATIVE STUDY OF MORETUS AND TYCHO CRATERS: INSIGHT INTO CRATER DEGRADATION PROCESSES. G.S. Klingenberg, W. Iqbal, L. Wueller, C. H. van der Bogert, and H. Hiesinger, Institut für Planetologie, Universität Münster, Wilhelm-Klemm-Str. 10, 48149 Münster, Germany, ([email protected]). Introduction: Geological maps are essential for illustrating the distribution of geologic materials and understanding the processes of their formation. Currently, there is heightened interest in the lunar south circumpolar region (SCR), due to its proximity to the South Pole Atkin (SPA) basin and presence of permanently shadowed regions (PSRs). With science and engineering goals in mind, there has recently been interest in evaluating locations for the establishment of a permanent base, such as the International Lunar Research Station (ILRS, [1]). For planning, guiding such missions, including the selection of landing sites and gaining an understanding of the surface is of utmost importance. Thus, we are constructing the first high-resolution geomorphological map of the ~116 km diameter Moretus crater (MC) (Fig.1) in the southern lunar highlands. During the mapping process, we are also comparing the morphological characteristics and degradation states of MC to Tycho crater (TC). Since TC is known to have formed about 100 Ma ago in the Copernican period [e.g., 2], we can assess the freshness of characteristic crater morphologies, such as impact melt pools/flows or the crater rim, to help infer an age for MC and gain a better understanding of the time frame for the disappearance of certain crater features. To date, the age of MC is uncertain, proposed to have formed either in the Eratosthenian [3] or Imbrian period [4]. Datasets and Mapping Technique: To create a geomorphological map of MC, we mapped at a scale of 1:100,000.and we are utilizing ESRI’s ArcGIS Pro 3.1 for initial slope and roughness analysis. We also used QGIS 3.30.0 with the Plugin “Mappy” [5] for creating the mapping unit polygons. We used Kaguya Terrain Camera (TC) orthophotography imagery at ~10 m/px [6], Chang’e-2 Digital Surface Models (DSM) at ~7 m/px [7], Chang’e-2 Digital Elevation Models (DEM) at ~7 m/px [8], and LRO Lunar Orbiter Laser Altimeter (LOLA) data at ~186 m/px [9]. Geomorphological Units: The differentiation and classification of morphological structures follows the unit classification process of [2] for Tycho crater. The units are divided into six groups with subdivisions for the transitional floor materials. Hummocky floor material: The hummocky areas are identified by their hilly and uneven surface texture. They can be interpreted as mega blocks of the collapsing crater wall. Due to their overall smooth appearance, they are interpreted to be superposed and covered by crater floor materials. Transitional floor materials: The hummocky floor material is mostly separated from the smooth floor material by two transitional units named rough floor material and intermediate floor material. Both units are primarily identified by their uneven textured and subdued surface features. In some cases, the intermediate material appears to have a higher albedo than the surrounding smooth floor material. The rough floor materials are interpreted to be covered mega blocks of the crater floor. Smooth floor material: The smooth floor materials have an overall lower albedo and can be interpreted as impact melt. The smooth floor materials are also characterized by subdued impact craters with blurred crater rims. The smooth floor low materials were added to highlight regions of the intermediate floor materials. They lack the rough, hummocky texture of the surrounding area and instead exhibit a smooth, uniform appearance. They are also isolated from the smooth floor materials of similar morphology. Central peak material: The central peak unit is identified by its elevation and isolated appearance in the centre of MC. The central peak has an elevation of ~2.6 km in respect to the surrounding crater floor, has steep slopes with an average angle of 20-25°. The northand west facing walls show cliffs with slope angles up to 70° which are marked by rockfalls and their linear paths downhill. Crater wall material: The crater wall is characterized by scarps and terraces. The scarps have slopes of ~25-38°, while the terraces have slopes of ~0-14°. There is a difference in width between the N/NE and S/SW crater walls. While the N/NNW wall has a width of ~14 km, the SE/SW wall reaches a width of ~ 20 km in isolated cases up to 25 km. Crater rim: The rim of MC has a sharp appearance and is very well traceable. The crater rim is surrounded by a ~2-22 km wide crater rim area which differs from the continuous ejecta blanket by a more textured appearance and by its more elevated topography (between 400 m up to 1400 m difference in elevation). The smaller widths are located towards the N, while the greater widths are located to the SW/SE. Continuous ejecta material: The continuous ejecta deposit is characterized by a subdued and uneven surface. On top of these surfaces grooves and sinuous features are visible extending radially outward from the MC rim. Conclusion and Outlook: Our 1:100,000 scale geomorphologic map is the first map of MC at this resolution, providing a detailed study of the morphologic features. The map allows investigations of crater degradation processes for a better understanding of age-related degradation states. Future work includes the selection of areas for crater sizefrequency distribution measurements that can be compared with previous work. Investigations of the overall geometry and appearance will be used to assess the possibility of MC being an oblique impact. References: [1] Hu et al. (2023) P&SS 227. [2] Krüger et al. (2016), Icarus 273, 164-181. [3] Fortezzo et al. (2020) LPSC 51, #2760. [4] Krasilnikov et al. (2023) SSR 57, #2. [5] Penasa et al. (2020), EPSC 2020, #1057. [6] Haruyama et al. (2009) LPSC 40, Abstract#1553. [7] Chang’e 2 global digital orthophoto dataset, NAOC (2019). [8] Chunlai et al. (2018) Geomatics and Information Science of Wuhan University 43, Abstract#4, [9] Barker M. K. et al. (2016) Icarus 273, 346-355. Fig. 1 (A) LRO WAC image of Tycho crater, (B) Kaguya TC image of Moretus crater, (C) Geomorphological map of Tycho crater [2], (D) Geomorphological map of Moretus crater (this work).