A fragile record of fleeting water on Mars

The light-toned sedimentary layers that outcrop widely throughout Mars’ Southern Highlands have long been an enigma in uncovering the climatic history of Mars. Although these units seem to contain unique records of fluctuating surface conditions, the role of water in their formation is debated. A distinctive property of many such deposits is their elevated thermal inertia relative to that of surrounding materials. This temperature-controlling trait is often interpreted to indicate induration resulting from aqueous processes. However, prevalent erosional landforms suggest that the deposits host much weaker materials than neighboring units. We address this apparent contradiction by disentangling the relationships between thermal inertia, mineralogy, and erosion susceptibility and by quantifying the cohesion of layered deposits in the Arabia Terra region. We demonstrate that variations in dust cover associated with relative erodibility and eolian abrasion can be inconspicuous controls on apparent thermal inertia. We ultimately find that these deposits are not as cohesive as would be expected from a high water-to-rock ratio setting either during or after deposition. If water-rich surface conditions existed in the region after the Noachian, these deposits suggest they may have only been intermittent and fleeting.