Hypervelocity Impact Experiments in Iron‐Nickel Ingots and Iron Meteorites: Implications for the NASA Psyche Mission

Abstract

The National Aeronautics and Space Administration (NASA) Psyche mission will visit the 226-km diameter main belt asteroid (16) Psyche, our first opportunity to visit a metal-rich object at close range. The unique and poorly understood nature of Psyche offers a challenge to the mission as we have little understanding of the surface morphology and composition. It is commonly accepted that the main evolutionary process for asteroid surfaces is impact cratering. While a considerable body of literature is available on collisions on rocky/icy objects, less work is available for metallic targets with compositions relevant to Psyche. Here we present a suite of impact experiments performed at the NASA Ames Vertical Gun Range facility on several types of iron meteorites and foundry-cast ingots that have similar Fe-Ni compositions as the iron meteorites. Our experiments were designed to better understand crater formation (e.g., size, depth), over a range of impact conditions, including target temperature and composition. We find that the target strength, as inferred from crater sizes, ranges from 700 to 1,300 MPa. Target temperature has measurable effects on strength, with cooled targets typically 10-20% stronger. Crater morphologies are characterized by sharp, raised rims and deep cavities. Further, we derive broad implications for Psyche's collisional evolution, in light of available low resolution shape models. We find that the number of large craters (>50 km) is particularly diagnostic for the overall bulk strength of Psyche. If confirmed, the number of putative large craters may indicate that Psyche's bulk strength is significantly reduced compared to that of intact iron meteorites. Plain Language Summary Many iron meteorites are thought to be remnants of the cores of melted asteroids. Some cores may have been exposed by collisions during the earliest days of Solar System history, with a few survivors possibly found today in the main asteroid belt. National Aeronautics and Space Administration (NASA) Psyche mission will be the first spacecraft to visit asteroid (16) Psyche, an object thought to be representative of these metallic asteroids. Impacts onto (16) Psyche in the past may therefore be able to tell us about the history and nature of this body. To this end, we performed high-speed impact experiments into metallic targets in order to understand how crater formation differs from rocky bodies. These experiments revealed that impact craters into metal targets are deeper and have sharper rims than on their rocky counterparts. These results will be crucial for interpreting both the bulk properties of Psyche's interior and the modification of Psyche's surface when the Psyche mission reaches its target.