Experiments On Sublimating Carbon Dioxide Ice And Implications For Contemporary Surface Processes On Mars

Abstract

Carbon dioxide is Mars’ primary atmospheric constituent and is an active driver of Martian surface evolution. CO2 ice sublimation mechanisms have been proposed for a host of features that form in the contemporary Martian climate. However, there has been very little experimental work or quantitative modelling to test the validity of these hypotheses. Here we present the results of the first laboratory experiments undertaken to investigate if the interaction between sublimating CO2 ice blocks and a warm, porous, mobile regolith can generate features similar in morphology to those forming on Martian dunes today. We find that CO2 sublimation can mobilise grains to form (i) pits and (ii) furrows. We have documented new detached pits at the termini of linear gullies on Martian dunes. Based on their geomorphic similarity to the features observed in our laboratory experiments, and on scaling arguments, we propose a new hypothesis that detached pits are formed by the impact of granular jets generated by sublimating CO2. We also study the erosion patterns formed underneath a sublimating block of CO2 ice and demonstrate that these resemble furrow patterns on Mars, suggesting similar formation mechanisms.

How martian araneiforms get their shapes: morphological analysis and diffusion-limited aggregation model for polar surface erosion

“…These new dendritic troughs are found in the southern hemisphere. They are similar in the scale to northern furrows -small shallow branching channels -observed on northern dunes (Bourke, 2013;Mc Keown et al, 2017). The same seasonal phenomena (fans, cracks, spring albedo variations, etc.)…”

Martian gullies: a comprehensive review of observations, mechanisms and insights from Earth analogues

“…The authors use a field-simulation analogue to support their hypothesis, where the authors placed decametre-scale sublimating blocks of CO2 ice on terrestrial dunefields ( Figure 25) and produced similar narrow leveed channels (and terminal pits). These pits have also been reproduced in laboratory simulations with sublimating blocks of CO2 ice (Mc Keown et al, 2017). As discussed in Sections 2.1 and 2.6, the peculiar morphology and precise timing of the activity of linear gullies suggests that their formation process is different from the other martian gullies, so this mechanism has not been applied to the general population of gullies.…”

CO 2 sublimation in Martian gullies: laboratory experiments at varied slope angle and regolith grain sizes

“…Dundas et al 2010Dundas et al , 2014Dundas et al , 2017Johnsson et al 2014;de Haas et al 2015b) require some viscosity or fluidization of the flow beyond that of a simple granular flow. Further, in linear gullies the new morphologies are complex, encompassing albedo changes, formation of pits, channels with levees and complex distributary networks on relatively low slopes (Diniega et al 2013;Pasquon et al 2016;this volume, in review;McKeown et al 2017;Jouannic et al, this volume, in review). As discussed by Stewart & Nimmo (2002), CO 2 gas should dissipate too quickly to enable durable fluidization of a sublimationtriggered flow.…”

“…Recent studies suggest that seasonal freezing and sublimation of CO 2 ice could be responsible for present-day gully activity on Mars (Diniega et alassociate the timing of morphological changes with the seasonal CO 2 cycle (Reiss & Jaumann 2003;Dundas et al 2010Dundas et al , 2012Dundas et al , 2014Reiss et al 2010;McEwen et al 2011;Raack et al 2015;Vincendon 2015;Pasquon et al 2016) while experimental simulations (Diniega et al 2013;Sylvest et al 2016;McKeown et al 2017) and numerical simulations (Cedillo-Flores et al 2011;Pilorget & Forget 2016) demonstrate the efficacy of CO 2 slope mobilization models.…”