Investigation of morphology and impact ejecta emplacement of the Copernican Das crater on the lunar farside

Abstract

This study investigates the morphology and ejecta emplacement dynamics of the Copernican-aged Das crater on the lunar farside. High-resolution panchromatic images, and spectral, and topographic data from lunar orbiter missions were utilized for the study. The identified morphological features in the crater such as central peaks, wall terraces, and impact melt deposits reflect how impact event interacted with the lunar surface. Based on our findings and existing knowledge of cratering processes, we discuss the stages in the evolution of the Das crater, involving excavation, rebound effects, wall collapse, and cavity modification. The impact melting that occurred during cavity modification significantly influences crater morphology and structural features such as central peaks and hummocky floor deposits. The effects of voluminous melting are also seen in the late-stage flow emplacement and rim veneers. Floor subsidence and structural adjustments, driven by extensive slumping and terrace formation, further shape the morphology of the crater. We propose a multi-stage process for ejecta emplacement during crater formation. The contiguous ejecta blanket forms via ballistic sedimentation in the excavation stage, followed by melt-ejecta emplacement in subsequent stages. The asymmetric distribution of ballistic ejecta around Das crater, notably the lack of secondary crater chains in the NNE direction, implied an oblique impact. This asymmetry, along with the circularity of the crater, indicated an impact direction from NNE to SSW, with an angle of 15°–25° relative to the horizontal. The crater elongation in the east-west direction results from post-impact modifications rather than the impact trajectory. The distribution of melt deposits is mainly concentrated in the eastern part of the crater, contrary to an expected downrange emplacement. This phenomenon is attributed to asymmetric cavity modification processes facilitated by pre-impact topographic asymmetry. Overall, these findings highlight the complex interplay between impact dynamics, topographic features, and post-impact modification processes in shaping the morphology of lunar craters, providing valuable insights into lunar surface evolution and impact cratering processes.