Depth to Diameter Relationships for <50 m Diameter Martian Craters

Impact craters provide key information about the geological history of planetary surfaces. Small craters are particularly useful for determining the target properties and for quantifying erosion rates. On Mars, few studies have been conducted on small craters, especially on their shapes, and little is known about their morphometry. Here, we address this problem using high-resolution orbital data. We mapped $\sim$80,000 craters with diameters below 50 m over two types of terrains found in Valles Marineris: landslide deposits and Interior Layered Deposits (ILDs). We computed six morphometric relationships from the measurements of the crater depth $d$ and apparent diameter $D_{\text{app}}$ for each terrain, in the form $d=c{D}_{\text{app}}^{\alpha }$. We found a linear relationship $\left(\alpha \sim 1\right)$ linking depth and diameter for both terrains, in good agreement with previous results for simple craters over 50 m and below 5 km. We obtained a lower value for $c$ for ILDs, highlighting that freshest craters from our population are shallower than expected for newly formed craters. Hence, we suggest that erosion is the dominant mechanism over the target properties to explain the observed crater shapes, especially for ILDs. The computed morphometric relationships can be used to better constrain the initial crater shapes for small diameters. Our study also highlights the limits of manual crater mapping and paves the way for the use of automatic algorithms to count and map craters in future works.