1 Introduction
The NASA Psyche mission is scheduled to launch in 2022. The 225-km asteroid Psyche was chosen as the mission target because remote sensing data (radar, density, etc.) indicated a likely metallic composition (e.g., Konopoliv et al., 2011; Matter et al., 2013; Shepard et al., 2015). Previous missions have visited rocky asteroids at close range (e.g., Galileo , Dawn , Rosetta ) revealing that cratering is the primary evolutionary process of main belt asteroid surfaces. As such, the selection of the Psyche mission triggered an increased interest in the scientific community to better understand cratering into metallic materials relevant to asteroids (e.g., Marchi et al., 2020; Libourel et al., 2019; Raducan et al., 2020; Ogawa et al., 2021). These impact experiments have provided preliminary insight as to crater dimensions, depth, and overall morphology for iron meteorites and their lab made proxy Fe-Ni alloys, showing that cratering into Fe-Ni targets is remarkably different from rocky targets. Additional metallic targets, such as aluminum and copper, have been investigated (e.g., Horz et al., 1995; Burchell and Mackay, 1998, Hernandez et al., 2006; Daly and Schultz, 2018), but in light of these non-asteroidal compositions, their applicability to Psyche requires further consideration.
The selection of the Psyche mission also prompted continued telescopic observations. These observations, coupled with revised mass and shape modeling estimates, indicate that Psyche may contain less metal than previously thought. The current best interpretation of available data to date suggests that Psyche may have 30-60 vol.% metal (Elkins-Tanton et al., 2020). This conclusion primarily rests on revised mass (lower) and volume (larger) estimates combined with radar, spectral and thermal inertia observations. Psyche may be dominantly metallic (Fe-Ni alloys), but may contain up to 60% porosity (Elkins-Tanton et al., 2020) are notions used to explain the current best estimate of Psyche’ density (4.1-4.2 g/cm3, Ferrais et al., 2020). Alternatively, Psyche could be an assemblage made dominantly of Fe-Ni with up to 5-10 wt.% low-Fe silicates and 8-17 wt.% and ~35% porosity (Cantillo et al., 2021, Elkins-Tanton et al., 2020, Sanchez et al., 2017, Takir et al., 2017). The origin of extensive porosity on Psyche is not understood. A possibility is that porosity could be due to impact-generated fracturing perhaps as the result of one or more hit-and-run collisions with subsequent re-accumulation, and/or the result of billions of years of collisional evolution in the main belt. Interestingly, the hypothesis that Psyche may be heavily fractured is bolstered by our recent impact experiments on Fe-Ni targets (Marchi et al., 2020), in which impacts cause metal cracking thereby introducing significant bulk porosity. The applicability of these lab-scale experiments to Psyche, however, remains to be investigated.
Regardless of the specific nature of Psyche composition, impact processes are important for the evolution of the surface and have strong influences on overall bulk porosity, regolith generation and projectile implantation onto a metallic object. To investigate how impacts alter the surface of metal-rich bodies, like Psyche, we compare small-scalein situ high-velocity experiments (Marchi et al., 2020) to simulated crater morphologies. In this work, we benchmark iSALE and CTH shock physics codes in 2D against our in situ high-velocity impacts on Fe-Ni targets. We compare results from iSALE and CTH and evaluate strengths and limitations of both codes for specific planetary applications, such as large-scale collisions on asteroid Psyche.