Tag: ta2.20

20-EPN-015: Deciphering fluidization of mass flows by metastable volatiles on extra-terrestrial bodies

Project lead: Tjalling de Haas. Visit by Lonneke Roelofs, Utrecht University, the Netherlands to TA2.20 Open University Mars Chamber (UK).
Dates of visit: 20 September – 29 October 2021

Report Summary: Martian gullies are alcove-channel-fan systems that have been hypothesized to be formed by the action of liquid water and brines, the effects of sublimating CO₂ ice, or a combination of these processes. Recent activity and new flow deposits in these systems have shifted the leading hypothesis from water-based flows to CO₂-driven flows, as it is hard to reconcile present activity with the low availability of atmospheric water under present Martian conditions. Direct observations of flows driven by metastable CO₂ on the surface of Mars are however nonexistent, and our knowledge of CO₂-driven flows under Martian conditions remains limited. For the first time, CO₂-driven granular flows were produced in a small-scale flume under Martian atmospheric conditions in the Mars Chamber at the Open University (UK). The experiments were used to quantify the slope threshold and CO₂ fraction limits for fluidization. With these experiments, we show that the sublimation of CO₂ can fluidize sediment and sustain granular flows under Martian atmospheric conditions. The morphology of the deposits is lobate and depends highly on the CO₂-sediment ratio, sediment grain size, and flume angle. The gas-driven granular flows are sustained under low (<20^o) flume angles and small volumes of CO₂ (around 5% of the entire flow). Pilot experiments with sediment flowing over a layer of CO₂ suggest that even smaller percentages of CO₂ ice are needed for fluidization. The data further shows that the flow dynamics are complex with surging behavior and complex pressure distribution in the flow, through time and space.

Article in the Europlanet Magazine on visit by Lonneke Roelofs.

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20-EPN-038: The strange behaviour of highly viscous mud in the low pressure environment: why the mixture changes its volume?

Visit by Petr Brož, Institute of Geophysics of the Czech Academy of Science (Czech Republic) to TA2.20 Open University Mars Chamber (UK).
Dates of visit: 6-17 December 2021

Report Summary: We performed multiple mud experiments inside a low-pressure chamber to investigate whether the volume of mud changes once exposed to the reduced atmospheric pressure of Mars. Our results show that mud extruded onto the surface under martian environmental conditions increases its volume and hence behaves differently than on Earth. The low atmospheric pressure causes instability of the water present in the mud mixture, leading to the formation of bubbles, which increase the volume of the mud.

These bubbles are then trapped within the mud. The buoyancy of the bubbles is not sufficient to overcome the drag force within the viscous material and rise to the surface. Hence, these bubbles remain trapped and gradually grow up to centimetre scale sizes. During their growth they push the mud out of the container resulting in horizontal and vertical inflation of the mud surface over cm-scales.

This behaviour is not observed at terrestrial mud flows, but it is somewhat similar to volumetric changes associated with degassing of some terrestrial lavas or mud volcano eruptions. Our experimental approach hence shows that viscous mud exposed to reduced atmospheric pressure behaves differently to on Earth.

Full scientific report published by kind permission of Petr Brož.

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