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12In situ extraterrestrial samples returned for study (e.g., from the Moon) are crucial in 13 understanding the origin and evolution of the Solar System as, contrary to meteorites, they 14 provide a known geological context for the samples and their analyses. Asteroid 25143 Itokawa 15 is a rubble pile asteroid consisting of reaccumulated fragments from a catastrophically disrupted 16 monolithic parent asteroid, and from which regolith dust particles have been recovered by the 17 Hayabusa space probe. We analyzed two dust particles using Electron Backscatter Diffraction 18 (EBSD) and 40 Ar/ 39 Ar dating techniques. One of the grains showing signs of 15-25 GPa impact 19 shock pressure, yielded a 40 Ar/ 39 Ar plateau age of 2.3 ± 0.1 Ga. We develop a novel temperature-20 pressure-porosity model, coupled with diffusion models to show that the relatively low pressure 21 and high temperature involved in the impact process can be reconciled only if the asteroid was 22

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