Search

The Kieffer model is a widely accepted explanation for seasonal modification of the Martian surface by CO _2 ice sublimation and the formation of a “zoo” of intriguing surface features. However, the lack of in situ observations and empirical laboratory measurements of Martian winter conditions hampers model validation and refinement. We present the first experiments to investigate all three main stages of the Kieffer model within a single experiment: (i) CO _2 condensation on a thick layer of Mars regolith simulant; (ii) sublimation of CO _2 ice and plume, spot, and halo formation; and (iii) the resultant formation of surface features. We find that the full Kieffer model is supported on the laboratory scale as (i) CO _2 diffuses into the regolith pore spaces and forms a thin overlying conformal layer of translucent ice. When a buried heater is activated, (ii) a plume and dark spot develop as dust is ejected with pressurized gas, and the falling dust creates a bright halo. During plume activity, (iii) thermal stress cracks form in a network similar in morphology to certain types of spiders, dendritic troughs, furrows, and patterned ground in the Martian high south polar latitudes. These cracks appear to form owing to sublimation of CO _2 within the substrate, instead of surface scouring. We discuss the potential for this process to be an alternative formation mechanism for “cracked” spider-like morphologies on Mars. Leveraging our laboratory observations, we also provide guidance for future laboratory or in situ investigations of the three stages of the Kieffer model.

The role played by transient impact-induced endogenous brines in the formation of geomorphic features has been proposed on airless worlds such as Europa, Vesta, and Ceres, as well as on worlds with thin atmospheres such as Mars. After liquefaction, the hypothesized brines flow in a debris-flow-like process, incising curvilinear gullies and constructing lobate deposits within newly formed craters. Here we investigate what parameters (if any) could enable liquid to be transiently present for a sufficient time (∼tens of minutes) under postimpact transient atmospheric pressures (10 ^−4 –10 ^−5 torr) to form curvilinear gullies and lobate deposits, as have been seen on Vesta and more tentatively Ceres. We report that water likely vacuum-freezes too quickly, while NaCl brine enables flow longevity. We also find that frozen lid formation facilitates longer liquid lifetimes, as with lava in terrestrial lava tubes and model predictions for cryovolcanic flows on Europa. This work provides additional contributions to the growing body of literature that investigates the role of transient brines in sculpting the surfaces of airless worlds.