Formation of ultrafine particles from impact-generated supercritical water

Shock-recovery experiments were performed targeting an olivine, iron, and water mixture to simulate a low-velocity ocean impact event. The maximum pressure in the sample container reached 20 GPa during the experiments. Ultrafine particles (UPs) of olivine and metal oxides were newly formed, even at pressures less than their vaporization pressure (150-200 GPa). Impedance-match and thermodynamic calculations suggest that supercritical water formed during the shock wave traversal. Such supercritical water dissolves impacted materials and precipitates UPs. Results of our experiments further suggest that many extraterrestrial objects that have impacted on oceans might have been converted to large masses of UPs and probably influenced the climate and UV shielding, especially during the late Hadean and early Archean eras.