Impact cratering experiments with metallic targets: Ejecta
Abstract
The parent bodies of iron meteorites are thought to have formed early in the terrestrial planet region, differentiated, and migrated to the main asteroid belt [1]. Asteroid (16) Psyche, the target of the NASA mission, is one of the most iron-rich asteroids and could be a remnant of the core of a differentiated body [2]. The surface of iron-rich bodies should have been modified by hypervelocity impacts, i.e., covered by craters and fallback ejecta. To obtain knowledge of impact ejecta from iron-rich bodies, we conducted laboratory impact experiments using iron meteorite, carbon steel, and iron-nickel alloy blocks and a two-stage hydrogen-gun at the Institute of Space and Astronautical Science (ISAS) [3]. In this study, the projectiles were rocks and pieces of metal with velocities ranging from 1.4 to 7.0 km/s. The targets were kept at either room temperature (RT) or below 150 K. The ejecta were investigated in terms of ejection velocities, size distribution, and shape. Our results showed that more fine ejecta were formed from the targets kept at 150 K than those at RT. There were ejecta with velocities lower than the escape velocity of Psyche, similar to the reported results for cratering on steel targets at room temperature [4], suggesting that there is iron-rich regolith on Psyche. The collected fragments were thin and had highly irregular shapes. The average axial ratio of the middle (b) and longest (a) axes (b/a) was 0.6-0.7 and was similar to those of rock fragments [5]; however, the shape was more angular than that of rock fragments, meaning a higher angle of friction of iron-rich regolith. Acknowledgments: This research was supported by the Hosokawa Powder Technology Foundation and by the Hypervelocity Impact Facility at ISAS/JAXA. References: [1] Bottke, W. F., et al., 2006, Nature 439, 821-824. [2] Elkins-Tanton, L. T., et al., 2017. In: 48th Lunar and Planetary Sci. Conf., abstract id.1718. [3] Ogawa, R., et al., submitted. [4] Katsura, T., et al., 2014, Icarus 241, 1-12. [5] Fujiwara, A., 1998, Nature 272, 602-603.
- Publication:
-
43rd COSPAR Scientific Assembly. Held 28 January - 4 February
- Pub Date:
- January 2021
- Bibcode:
- 2021cosp...43E.280N