Martian gullies: Produced by fluidization of dry material

TL;DR

This paper proposes a novel mechanism for Martian gully formation involving fluidization caused by CO2 sublimation, supported by experimental simulation, offering explanations for recurrent gully formation and formation on gentle slopes.

Contribution

It introduces a new fluidization-based model for Martian gullies, supported by experimental results, addressing limitations of previous hypotheses involving liquid water or dry flows.

Findings

Experimental simulation reproduces gully-like structures using air injection.

The proposed model explains recurrent gully formation and occurrence on slopes below the angle of repose.

Flow dynamics are consistent with Martian environmental conditions.

Abstract

The gullies on Mars were discovered in the year 1999.Since then several hypotheses have appeared trying to explain the presence of these gullies. The main hypotheses are the ones which suggest that some liquid, water or CO2, was responsible for modeling the gullies and ones that propose dry flows as the modeling agents. The aim of this work is to develop an alternative hypotetical mechanism of formation of Martian gullies.Our model proposes that the Martian gullies were formed as a result of a fluidization process of the material deposited on the slopes of the impact craters, plateaux and other geomorphologic structures. This fluidization is caused by the sublimation of carbon dioxide ice deposited in the form of snow, due to the daily and seasonal temperature changes. We also present the results of an experimental simulation.Structures similar to the Martian gullies were reproduced using the air injection mechanism, as a substitute to gaseous CO2, on a sandy slope. The Reynolds number for our experimental flow and for the flow in the Martian gullies was calculated and we found that they are of the same order, whilst the water flows have much higher Reynolds numbers.Taking into account the current environmental conditions for Mars, from our results it may be suggested that this mechanism is the possible modeling agent for the Martian gullies. Two of the most important characteristics of the proposed model are: a) It offers a simple explanation of how recurrent fluidization events occur in the same place, a necessary recurrence of the formation of a gully, offering a recharging mechanism for the system after every fluidization event, and b) It considers the formation of gullies possible even in angles smaller than the angle of repose. These characteristics of the model solve these two problems present in current theories.