Automatically Calculating Depths of Martian and Lunar Pits with Satellite Imagery

Pits, or pit craters, are roughly circular depressions found in planetary surfaces which are generally formed through gravitational collapse. Pits will be primary targets for future space exploration and habitability for their presence on most rocky Solar System surfaces and their potential to be entrances to sub-surface cavities. This is particularly true on the Moon and Mars where future astronauts will also be exposed to high radiation dosages whilst on the surface. However, since pits are rarely found to have corresponding high-resolution elevation data, tools are required for approximating their depths in order to find those which are the ideal candidates for exploration and habitation.We develop a tool that automatically calculates a pit’s apparent depth – the depth at the edge of its shadow - by measuring the shadow’s width as it appears in satellite imagery. The tool can produce a profile of the apparent depth along the entire length of the shadow, using just one cropped single- or multi-band image of a pit. Thus, allowing for the search for possible cave entrances to continue where altimetry or stereo image data is not available. Shadows are automatically extracted using k-means clustering with silhouette analysis for automatic cluster validation. We will present the results of testing the shadow extraction upon shadow-labelled Mars Reconnaissance Orbiter HiRISE imagery of Martian pits, as well as the findings of applying the tool to HiRISE images of Atypical Pit Craters (APCs) from the Mars Global Cave Candidate Catalog (MGC3) [1]. We will also present preliminary results of applying our tool to Lunar Reconnaissance Orbiter Narrow Angle Camera data taken of Lunar pits catalogued in the Lunar Pit Atlas [2].[1] – Cushing et al. (2015). Atypical pit craters on Mars: New insights from THEMIS, CTX, and HiRISE observations, Journal of Geophysical Research: Planets, 120, 1023–1043[2] – Wagner & Robinson (2021). Occurrence and Origin of Lunar Pits: Observations from a New Catalog, in 52nd Lunar and Planetary Science Conference, Lunar and Planetary Science Conference, p. 253