Simultaneous Detection of the Size and Velocity of the Largest Ejecta Particles with Velocities Exceeding 1 km s⁻¹

Impact ejecta with velocities exceeding the escape velocity of planetary bodies become meteorites and dust particles in interplanetary space. We present a new method that allows simultaneous measurement of the size and velocity of the largest high-velocity ejecta. High-speed camera images revealed the time required for the ejecta to reach the secondary target, and ejecta size was determined after the experiment by analyzing the craters formed upon their impact on the secondary target. We defined the size–velocity relationships of submillimeter ejecta with velocities exceeding 1 km s⁻¹, focusing on the largest detectable ejecta in our experiments. The results show that millimeter-sized meteoroids impacting the rocky surfaces of planetary bodies at 7 km s⁻¹ eject particles up to a few tens of micrometers in size toward interplanetary space at velocities exceeding the escape velocity of the body, even when it is greater than 1 km s⁻¹.