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.