Workshop on Martian Gullies: Theories and Tests (2008)
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MARTIAN GULLIES CREATED BY FLUIDIZATION OF DRY MATERIAL. Y. Cedillo-Flores1, 2, H. J. Durand-Manterola1, and R. A. Craddock 3 . Departamento de Física Espacial, Instituto de Geofísica, Universidad Nacional Autonoma de Mexico. UNAM. Coyoacan C.P 04510. D.F. Mexico1. (
[email protected]), (
[email protected]). Posgrado de Geografía, Facultad de Filosofía y Letras, Universidad Nacional Autonoma de Mexico. Circuito Interior. Ciudad Universitaria s/n. C.P 04510. D.F. Mexico2. Smithsonian Institution. Nacional Air and Space Museum. Room 3762. 6 th Street and Independence Avenue SW. Washington D.C. 20560-0315 3 (
[email protected]).
Introduction: Since the discovery of the Martian Gullies [1] several different theories try to explain their origin. However the formation of these features remains poorly understood, and distinctive morphologic variations exist that have often been ignored. The models based on the water, are somewhat controversial since the location of the gullies also appears in regions of very low temperature like so that the water in liquid state has taken part. Here we present a new model and the experimental results that attempt to create Martian gullies through gaseous fluidization of CO2 using mixtures of dry granular material and CO2 ice. Descrption of the model. Our model suggests this mechanism for the formation of these gullies: On Mars flows of dry material mixed with dry ice may result from the accumulation of CO2 ice and dust on slopes during the winter. Increases in temperatures during the spring may cause the CO2 ice to sublime initiating slope failure and mass-wasting. Based on our experimental data and observations, we suggest that the formation of at least some gullies may be analagous to pyroclastic flows but colds. Experiments. Our objectives when making the experiments in laboratory were to produce the fluidization of the sand by gas and to try to reproduce structures type gullies. We constructed a slope with volcanic dry sand. Tubes of 6 mm of diameter perforated in their surface each 9 mm were buried to 4 cm of depth parallel to the surface of the slope. By these tubes was injected air that bubbled in the sand, allowing that this fluidize and flow like a liquid by the slope (Fig. 1). The air in the laboratory is the substitute of the gaseous CO2 that is coming off when the carbonic ice being sublimated in Mars. The structures that formed in the laboratory are comparable with the Martian gullies (Fig. 2). Methodology. Using Mars Orbiter Camera (MOC), Thermal Emission Imaging System (THEMIS) and High Resolution Imaging Science Experiment (HiRise) 28 images and data, we identified 12 gullies with morphologic characteristis similar to those produced from our experiments. These gullies range occur at mid-latitude regions (33° to -71°) and at a range of elevations (-4800 to 2700 meters).
Fig. 1 A gully created by fluidization of dry material. Of the results of this experiment it can be observed that the fluidization produces sliding of the sand.
Fig. 2 Comparing the experimental gullies (left) with some Martian gullies (right), several similarities like narrow and winding channels, wide alcoves, wide, narrow and lobate aprons are appraised, similar to which exhibits several Martian gullies.
Workshop on Martian Gullies: Theories and Tests (2008)
The different elevation and latitudes in which we found gullies suggest that their existence can be explain by our model. Discussion: If it existed liquid water on the Martian surface, it had occurred in a very old geologic stage and nevertheless the gullies seem to be young. This appearance is due to the almost absence of small superposed craters of impact in the channels and the cones of detritus and by the comparison of these characteristics with the rest of the Martian surface. Those very old gullies possibly formed by stages during different cycles of high obliquity, between 105 to 106 years [1] to variations from 15º from 35º when the melted water ice was transported towards the poles. The gullies later to the dense atmosphere stage had to form by other processes, without intervention of some liquid. The type of morphology periglacial that is observed in numerous regions with gullies suggests frost weathering processes gave rise to the formation of eroded slopes that would represent the first stages of the formation of the gullies. Our model explains better the formation of gullies to different latitudes and in different lands and different directions since the formation processes are external and are adapted to the present conditions of the planet. The existence of gullies without intervention of a liquid is possible since recently the discovery of gullies in the Moon was reported, [2] where the nonexistence of some liquid in its surface is evident due to the extreme conditions of the satellite.
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Conclusions. Our scenario allows the formation of gullies in recent times and to a more extensive rank of latitude of what predict the models that require the liquid water presence. By our experimental results we concluded that the fluidized sand by CO2 is a feasible mechanism to form the gullies in diverse geologic and latitudinal settings and to any altitude. References: [1] Malin, M.C. and Edgett, K.S. (2000). Science, 288, 2330-2335. [2] Bart W. D. (2006). Lunar and Planetary Science XXXVII. Abstract #1345.
