Microclimate governs the morphology of sediment flows on Mars.

Landforms created by flowing water with sediment have left deposits on the surface of Mars, allowing study of the ancient environment. These features could provide constraints on surface water activity and past habitability. However, only a few lab studies have investigated the appearance and behavior of sediment-rich flows at relevant Mars surface conditions. We conducted experiments in a Mars environment chamber to understand the rheology and deposit morphology of mud under atmospheric pressures from 5 to 1000 mbar and surface temperatures between 248 and 297 K. We found that sediment flows in the Noachian era, when most aqueous activity occurred, could behave similarly to Earth analogs, but only under certain climate conditions. However, in the Hesperian and Amazonian periods, the dominant physical regime changed due to global atmospheric loss. Sediment flows during these eras would not have been similar to Earth analogs, and would have been dominated by freezing, evaporative cooling, and boiling depending on the microclimate (local pressure and temperature). Thus, regional climate and compositional context are important factors for interpreting satellite remote sensing images of these features on Mars. The results suggest we may be able to discover the paleo-atmospheric pressure record on Mars by analyzing sediment flow morphology.