Influence of small-scale topography on seasonal activity in martian polar regions: a study using HiRISE digital terrain models (DTM).

Abstract:

Every winter, a layer of CO2 ice forms at the poles of Mars. In spring, solar energy penetrates this layer and sublimes CO2 from underneath. This gas pressurizes and will eventually break through the ice at local weaknesses, causing a CO2 gas jet. While moving towards the vent, the compressed gas erodes substrate and picks up loose regolith particles, which is then deposited on top of the ice by the jets in the form of dark deposits. Repeated eruptions erode the underlying substrate, producing the so-called araneiform terrain (colloquially called martian “spiders”). These processes have no analog on Earth. The High Resolution Imaging Science Experiment (HiRISE) camera of the Mars Reconnaissance Orbiter mission is monitoring araneiforms and yearly seasonal re-appearance of fans and blotches, providing spatial and temporal distribution of eruptions, and activity levels in different regions of interest (ROI) around the martian south pole.

We investigate how topography, solar energy input, and time-dependent shadowing influence the distribution of the activity. The current paradigm states that CO2 jet activity and subsequent araneiform formation is driven mainly by solar energy. We use digital terrain models (DTMs) produced from HiRISE stereo images together with SPICE calculations of the local Sun’s position to create insolation maps. These maps account for surface slope and aspect as well as shadowing due to topographical features, with the DTM spatial scale of up to 1 m/pixel. This resolution allows us to resolve insolation at the smallest topographical features, e. g. araneiform troughs and isolated boulders. We correlate the amount of energy received over martian hours, days, or a complete season with CO2 jet activity nearby and thus determine why some areas are more active spatially or temporally than others.

We will discuss the pipeline for production of insolation maps and present them for several HiRISE monitored ROIs, compared with the spatial distribution of araneiforms. We aim to determine if the current insolation is correlated with the density of araneiform terrains in different ROIs. This project improves our understanding of CO2-related seasonal processes unknown to Earth, how they currently modify martian surfaces, and thus how they participate in the geological record of martian polar surfaces.