Fig. 7: Micrometeoroid size estimation.
A A provenance plot (left half) and a snapshot (right half) at the time when t = 50 ts, where t is the time after the initial contact and ts is the characteristic time for projectile penetration defined by the projectile diameter divided by the impact velocity. The impact velocities are shown in each panel. The spatial scale is normalized by the projectile radius. The target is a flat surface. Residual temperatures in the region of maximum pressure <1 GPa are not calculated (white area). The yellow-colored regions indicate residual temperatures greater more than 1000 K. B Heated volume above 1000 K normalized by the projectile one as a function of impact velocity. We used the expected residual temperatures (see Methods) to estimate the heated volumes at given impact velocities. The results depend on the choice of the EOS models. Two dashed black lines are the upper and lower bounds. C The estimated projectile diameter as a function of impact velocity. We used the two dashed lines in the (B) in this calculation. The hatched region is an allowable range of the combination between the projectile diameter and impact velocity. The heated volume on the Ryugu particle is estimated to be (1.6–6.3) × 10−16 m3 by assuming a cylindrical shape with the diameter of (10–20) μm and the thickness of 2 μm. The dimensions were determined with the microscopic images shown in Fig. 3.
