Abstract
Impact craters are a common geological feature found on a variety of planetary bodies throughout the Solar System and can reveal information about the history of the Solar System and its planets. Specifically, crater statistics can be used in age determination of planetary surfaces, and is currently the only tool available for such purposes. The calibration of the so-called cratering chronology models, from dated lunar samples and size-frequency distribution (SFD) makes it possible to derive more accurate absolute model ages for other planetary surfaces, including Mars. There are several processes that can alter the SFD, and one of them is target properties and this is especially apparent for craters in a smaller diameter range. Several studies have found that target properties, such as porosity, strength, cohesion, and friction play a major role on the final crater diameter size, but today´s knowledge is limited. In this study, a combination of numerical modelling and crater statistics was used to examine the effects of target properties (impact velocity and material) of small craters near the InSight landing site on Mars. The numerical simulations were conducted using the hydrodynamic code iSALE and in total, 128 models were computed for four different velocities and two different target materials, weak material (sand) and harder material (rock). The two model setups was selected based on THEMIS thermal data in the study area were areas with weak material (thought to be dust or sand) and rock, both basaltic in composition, were selected. This study shows that the impact velocity does change the final crater diameter, as expected from crater scaling laws. This is also the case between the two materials tested. While, for the lowest velocity tested (near the lower threshold of subsonic velocity) it fails to obey the expected power law relation between crater size and impactor diameter. In addition, cratering statistics and derivation of crater SFDs were performed for two areas with different target properties for the study area. The crater SFD show that the areas had the same age within the uncertainty, but had several changes in the slope, which could be a result of geological processes or human errors when conducting the crater counting. While, the coupling of the crater SFD with power-laws derived from the numerical models show that the change in slope of the two crater SFDs can possibly be explained by difference in target properties between the areas.