Impact phenomena of micrometeorites on lunar surface material

The NASA lunar surface samples 10019 and 10046 from the Apollo 11 mission were searched for micrometeorite impact craters by means of an optical reflecting microscope and a Stereoscan electron microscope. Craters with diameters between 2 microns and 0.8 mm were observed. Approx. 1 crater larger than 0.15 mm in diameter per 1 mm ² and 1 crater larger than 2 μm per 500 μm ² could be found. The time of exposure is calculated from crater number densities and cosmic dust influx values to be 10 000 yr and 100 yr for layers of respectivethicknesses. On lunar glassy spherules impact features were found which yield the same crater number densities. The phenomenology of high velocity impacts was studies by shooting microspheres on targets similar to lunar material using a 2 MV dust accelerator.