Micrometeorite bombardment simulated by ns-pulsed laser ablation: Morphological characterization of the impact craters

The term “space weathering” refers to processes that include changes in the physical, chemical, mineralogical, and spectral properties of the surface of asteroids, comets, and some planets and their satellites, such as the bombardment by micrometeorites, solar wind ions, and cosmic rays. In this study, we focus on micrometeorite impacts, which may be the primary contributor to the annual mass flow of material that reaches the surface of such bodies. Studying the processes and effects associated with micrometeorite impacts is fundamental for understanding the evolution of the solar system and its components. From an experimental point of view, it is typically assumed that micrometeorite impacts may be simulated by ns-pulsed lasers and, indeed, many experimental studies have been performed based on such assumption. These studies have the common main goal to understand how micrometeorite impacts may change the physical-chemical and spectral properties of the bombarded surfaces. However, here we perform the first experimental study dedicated to the morphological characterization of the impact craters created by ns-pulsed laser ablation, in order to determine how well ns-pulsed lasers simulate the crater morphology of natural micrometeorite impacts. For this purpose, the laser ablation technique was applied to three different silicates: feldspar, quartz, and jadeite. For each of these minerals, two ablation scenarios have been considered: in air and in water. The craters formed by ns-pulsed laser ablation were characterized, from the morphological point of view, using a profilometer. Using this data we estimated the depth:diameter ratio of each crater. The comparison with literature data shows that the simple craters formed by ns-pulsed laser ablation closely resemble craters formed by natural micrometeorite impacts. In other words, from a morphological point of view, ns-pulsed laser ablation is appropriate for the simulation of micrometeorite impacts. We additionally verified that the value of the depth:diameter ratio does not depend, within errors, on the total number of laser pulses or the repetition frequency, at least within the ranges covered in these experiments: i) between 1 and 1200 laser pulses and ii) between 1 and 10 Hz.