Cracks Forming in Frozen Martian Soil Simulant

This image shows an experiment conducted at NASA's Jet Propulsion Laboratory re-creating the processes that form spider-like features on Mars called araneiform terrain. The experiment involves carbon dioxide gas settling into Mars soil simulant. The gas settles between the grains of simulant and eventually freezes into ice. A heater underneath the soil simulant then warms up the ice and turns it back into gas. As pressure from the gas builds, the frozen top layer of simulant eventually cracks. When the pressure builds enough, a plume of carbon dioxide erupts. The study confirms several formation processes described by what's called the Kieffer model: Sunlight heats the soil when it shines through transparent slabs of carbon dioxide ice that build up on the Martian surface each winter. Being darker than the ice above it, the soil absorbs the heat and causes the ice closest to it to turn directly into carbon dioxide gas – without turning to liquid first – in a process called sublimation (the same process that sends clouds of "smoke" billowing up from dry ice). As the gas builds in pressure, the Martian ice cracks, allowing the gas to escape. As for what creates the spider legs, the Kieffer model suggests that as the gas vents, it carries a stream of dust and sand that scours the surface, forming scars that are revealed when the ice disappears in the spring. But the experiment also suggests an alternative explanation for the this part of the process: The researchers found that these formations could have also been created when ice formed in the pores within the soil, rather than on top of it, and that the release of gas from within this soil-ice mixture may have created the formations. The experiment took place in JPL's Dirty Under-vacuum Simulation Testbed for Icy Environments, or DUSTIE. https://photojournal.jpl.nasa.gov/catalog/PIA26406