Hypervelocity impact experiments in iron‐nickel ingots and iron meteorites: Implications for the NASA Psyche mission

1S. Marchi,1D.D. Durda,2C.A. Polanskey,3E. Asphaug,1W.F. Bottke,3L.T. Elkins‐Tanton,4L.A.J. Garvie,4S. Ray,1S. Chocron,4D.A. Williams
Journal of Geophysical Research (Planets) (In Press) Link to Article [https://doi.org/10.1029/2019JE005927]
1Southwest Research Institute, Boulder, CO, USA
2Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
3Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
4School of Earth and Space Exploration, Arizona State University, Tempe, AZ, USA
5Southwest Research Institute, San Antonio, TX, USA
Published by arrangement with John Wiley & Sons

The 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 1300 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.

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