Measurement of micron-sized ejecta generated from oblique impact experiments with regolith simulant targets

The surface of the Moon and other airless planetary bodies is usually covered by a regolith layer. The meteoroids and interplanetary dust particles bombarding such highly pulverized layer may excavate with a yield up to 1000 times of the impactor’s own mass. The excavated ejecta grains with relatively high speeds are the main components of the dust cloud around airless bodies. Faster grains with speeds exceeding the escape velocity of a planetary body contribute to the interplanetary dust environment.

In order to understand the formation of the dust cloud around airless planetary bodies, it is necessary to deeply understand how ejecta grains are launched from regolith surfaces. We performed new oblique impact experiments on particulate targets to determine the angular and size distributions of ejecta. The spherical Aluminum projectiles of 4 mm were fired by a light gas gun at speeds of around 4.1 km/s. The targets were B₄C powders with median diameters of 17 µm and the incident angles were 15°, 30°, and 45° to the target surface. Around the target, arrays of thin Al foils with thicknesses of 15 µm were installed, which were penetrated by high speed ejecta grains. The resulting holes were analyzed with computer vision methods. Our preliminary result is that we found (1) the sizes of major ejecta grains are comparable with median diameters of the target powder; (2) the angular distributions of ejecta varies with the incident angle of the impactor.