Is the Linné impact crater morphology influenced by the rheological layering on the Moon’s surface? Insights from numerical modeling

Elena MARTELLATO1, Valerio VIVALDI2,3, Matteo MASSIRONI2, Gabriele CREMONESE3,Francesco MARZARI4, Andrea NINFO5, and Junichi HARUYAMA6
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12892]
1Museum f€ur Naturkunde, Leibniz Institute for Evolution and Biodiversity Science, Invalidenstraße 43, 10115 Berlin, Germany
2Dipartimento di Geoscienze, Universita degli Studi di Padova, via Gradenigo 6, I-35131 Padova, Italy
3INAF-Osservatorio Astronomico di Padova, vic. Osservatorio 5, 35122 Padova, Italy
4Dipartimento di Fisica e Astronomia “Galileo Galilei,” Universita degli Studi di Padova, via Marzolo 8, 35131 Padova, Italy
5Dipartimento di Fisica e Scienze della Terra, Univerista di Ferrara, via Saragat 1, 44122 Ferrara, Italy
6Department of Solar System Sciences, Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency,Sagamihara, Kanagawa 252-5210, Japan
Published by arrangement with John Wiley & Sons

Linné is a simple crater, with a diameter of 2.23 km and a depth of 0.52 km, located in northwestern Mare Serenitatis. Recent high-resolution data acquired by the Lunar Reconnaissance Orbiter Camera revealed that the shape of this impact structure is best described by an inverted truncated-cone. We perform morphometric measurements, including slope and profile curvature, on the Digital Terrain Model of Linné, finding the possible presence of three subtle topographic steps, at the elevation of +20, −100, and −200 m relative to the target surface. The kink at −100 m might be related to the interface between two different rheological layers. Using the iSALE shock physics code, we numerically model the formation of Linné crater to derive hints on the possible impact conditions and target physical properties. In the initial setup, we adopt a basaltic projectile impacting the Moon with a speed of 18 km s−1. For the local surface, we consider either one or two layers, in order to test the influence of material properties or composite rheologies on the final crater morphology. The one-layer model shows that the largest variations in the crater shape take place when either the cohesion or the friction coefficient is varied. In particular, a cohesion of 10 kPa marks the threshold between conical- and parabolic-shaped craters. The two-layer model shows that the interface between the two layers would be exposed at the observed depth of 100 m when an intermediate value (~200 m) for the upper fractured layer is set. We have also found that the truncated-cone morphology of Linné might originate from an incomplete collapse of the crater wall, as the breccia lens remains clustered along the crater walls, while the high-albedo deposit on the crater floor can be interpreted as a very shallow lens of fallout breccia. The modeling analysis allows us to derive important clues on the impactor size (under the assumption of a vertical impact and collision velocity equal to the mean value), and on the approximate, large-scale preimpact target properties. Observations suggest that these large-scale material properties likely include some important smaller scale variations, disclosed as subtle morphological steps in the crater walls. Furthermore, the modeling results allow advancing some hypotheses on the geological evolution of the Mare Serenitatis region where Linné crater is located (unit S14). We suggest that unit S14 has a thickness of at least a few hundreds of meters up to about 400 m.

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