THE MORPHOLOGY OF MARTIAN IMPACT CRATERS IN 'SOFT' VS. 'HARD' TERRAIN

Impact crater morphology plays a critical role in the relative dating of impact craters. Subsequently, it is important to understand how the relative durability of the impacted substrate may affect impact crater morphology at the time of impact and as time goes on. We examined a series of nine craters, six in 'soft' terrain and three in 'hard' terrain, in order to determine if there were any noticeable morphological differences between the two crater environments. The soft-terrain impact craters were taken from the Medusae Fossae Formation, with two craters each representing the Upper, Middle, and Lower portions of the formation, whereas the hard-terrain impact craters were taken from the volcanic plains south of Arsia Mons.

A base map consisting of Context images captured by the Mars Reconnaissance Orbiter and taken from JMARS was first constructed for each impact crater using Adobe Illustrator. From these base maps, detailed geologic maps were constructed to mark the boundaries between separate layers of ejecta, features in crater interiors and the extent of secondary crater fields. Additionally, topographical profiles running north-south and west-east were constructed for the analyses. After examining each crater and profiling details regarding their impact histories and appearances, we compiled the data into a list containing similarities between the two impact environments. Martian impact craters in both soft and hard terrain shared similarities in the relative appearance and dimensions of their crater rims, crater interiors, and transient crater diameters and depths, as well as sharing the presence of fluidized ejecta. Four main differences were found between the two crater environments: Ejecta lobes in 'hard' terrain follow the shape of the crater closely, while soft-terrain ejecta lobes are more erratic in shape; there are visible textural differences in hard-terrain ejecta lobes, which correlate with the thickness of the surface material; the ejecta lobes of soft-terrain craters are more easily compromised by wind erosion and are less recognizable with age, while those of hard-terrain craters are easy to define regardless of age; and secondary crater fields surrounding soft-terrain craters are more prominent and easier to distinguish from surrounding craters than those in 'hard' terrain.