 EXPERIMENTAL SIMULATIONS OF RECURRENT SLOPE LINEAE ON THE SURFACE OF MARS.   H. Farris1, V. Chevrier1, J. Dixon1, and G. de Mijolla2, 1Arkansas Center for Space and Planetary Sciences, University of Arkansas, Fayetteville, AR, 2Smith College, Northampton, MA.   Introduction:  As seen by Mars Reconnaissance Orbiter HiRISE, recurrent slope lineae (RSLs) (Fig 1) are narrow (no longer than 5 meters), dark features seen on Martian slopes between 48°S and 32°S latitudes, extending beyond the regions which experience cyclical CO2 frost patterns.  Their ephemeral or seasonal appearance suggests a variety of hypotheses, one of which is formation caused by the existence of viscous brines near the surface [1].  Phoenix results showed the presence of ions like perchlorates [2], which alter the stability of such brines at low temperatures, as do regional freezing and evaporating, timescales, and presence of solid sediment [3]. Therefore, studies of liquid brine flows are vital in understanding geomorphological processes on the surface of Mars, specifically the formation of RSLs.    Fig 1: Example of RSLs taken by HiRISE at Newton Crater [1].  Previous low-viscosity flow simulations using pure water [4] salt-rich fluids [5], (Fig. 2) or water-ice slush [6] produced morphologies similar to gullies [7]. High viscosity solutions (~1 Pa.s) produced morphologies similar to RSLs or slope streaks [8]. Preliminary work using a cold room showed that low temperatures affect the progression of the flow, especially for higher viscosities [9]. In this work, we attempt to quantify the effect of low temperatures and viscosity on the morphology of the resulting flow features.       Methods:  To simulate the formation of these slope lineae, we used Natrosol, natural cellulose ether.  It is a commercial thickener that changes the viscosity of a fluid without altering its other properties.  We mixed different amounts of Natrosol with water using a magnetic stirrer for 1-8 hours, depending on the    desired viscosity of the resulting fluid.  The viscosity of the fluid was measured from viscosity ball drop   Fig 2: A. Previous experiments using about 100 mL of pure water, showing similar morphologies to Martian gullies [6], B, C, D. Flow features created with higher fluid viscosity (B) 100 mL, 1.0 Pa.s; (C) 200 mL, 1.0 Pa.s; (D) 200 mL, 0.07 Pa.s. E, F. Experiments run at 20°C with the following viscosity values (E) 1 Pa.s and (F) 0.75 Pa.s but on a 10° slope compared to 20° for all the other tests [7].  tubes.  We then added 3 to 4 drops of food coloring to the solution, thus adding to the contrast between substrate and solution.  We then ran 50mL of the solution down two wooden flumes using a funnel and a 15 cm long piece of polyethylene tubing with a 19 mm diameter.  One of the flumes was at room temperature with dimensions of 0.5x3 m2  and filled with Mars Mojave Simulant (MMS) (Fig 3).  The other one was at -20 degrees Celsius with dimensions of 0.9x1.5 m2  and filled with sand.  These flumes were first inclined at an angle of 20 degrees.  Then the experiments were repeated at an inclination angle of 10 degrees.  Once the features had dried or frozen, the width, length, and other relevant aspects of the features were measured in 5 cm increments.  Each run was performed twice and the values were averaged.   Fig 3: Wooden flume at room temperature used for slope lineae experiments Results:  The measurements were plotted in excel (Fig 4-6).    Fig 4: Average width of RSLs as a function of viscosity  As the viscosity of the liquid increased, the width of the RSLs increased in all cases (Fig 4), but was most dramatic in the cold room at a 10° slope.  The greatest variability in the data occurs at the highest viscosity (~1 Pa.s).    As the viscosity of the liquid increased, the length of the RSLs decreased in all cases (Fig 5), again, most dramatically in the cold room at a 10° slope. The ratio of average width to average length varied the greatest as a function of viscosity in the cold room at a 10° slope (Fig 6).    Fig 5: Average Length of RSLs as a function of viscosity  Discussion: The 20° slope runs remain relatively linear, while the 10° slope runs dramatically rise or drop initially and then smooth out, indicating length and width are more dependent on the slope of the substrate rather than the temperature of the environment.  This is especially interesting because the substrate varies from sand to MMS for the cold and room temperature experiments, respectively. Since, looking at the width and/or length of these features independently do not paint a complete   Fig 6: Ratio of average width to average length of RSLs as a function of viscosity  picture, the most useful information comes from the ratio of average width to average length.  The quicker the fluid (warmer, less viscous), the features become indistinguishable (Fig 6).  However, the slower the fluid (colder, more viscous), the resulting morphologies are vastly different.  The features which result from a 20° slope at room temperature have width only about 1/100th the length similar to Fig 2B, while the features which result from a 10° slope in the cold room have widths about 1/3rd the length similar to Fig 2F. Future Work: In addition to studying the effects of viscosity on the formation of RSLs, other parameters will also be looked at, as a means of creating a more robust model for the surface of Mars.  First, the substrates used will vary to include JSC-Mars 1 and perhaps even mixtures of all three substrates.  Also, we will examine the effects of environmental conditions on formation of RSLs.  As the surface freezes, thaws, and evaporates, the thermodynamic properties of the regolith change.  By introducing a layer of CO2 ice to the substrate, the effects of sublimation and evaporation can be noted.  Lastly, the introduction of larger grains to the substrate, representing boulders, would be more characteristic of actual Martian terrain.  RSLs have been seen in contact with such boulders and could cause local melting [1]. References: [1] McEwen, A.S., et al. (2011) Science, 333, 740-743. [2] Hecht, M.H., et al. (2009) Science, 325, 64-67. [3] Chevrier, V., et al. (2009) Geophys. Res. 114(E06001). [4] Addison, B.C., et al. (2010) LPSC, 41, #1399. [5] Coleman, K.A., et al (2008) LPSC, 39, #2240. [6] Coleman, K.A., et al (2009) Planetary and Space Sciences, 57, 711-716. [7] de Mijolla, G.M., et al. (2011) LPSC, 42, #1142. [8] Howe, K.L., et al. (2010) LPSC, 41, #1706. [9] Verdie, E., et al. (2008) Geophys. Res. 35(L21501). 0.5$ 1$ 1.5$ 2$ 2.5$ 3$ 3.5$ 4$ 4.5$ 0$ 0.2$ 0.4$ 0.6$ 0.8$ 1$ Av er ag e' Wid th '(c m)' Viscosity'(Pa's)' Average'Width' 20$deg.$slope,$ room$temp$ 20$deg.$slope,$ cold$temp$ 10$deg.$slope,$ room$temp$ 10$deg.$slope,$ cold$room$ 0" 20" 40" 60" 80" 100" 120" 140" 160" 180" 0" 0.2" 0.4" 0.6" 0.8" 1" 1.2" Av er ag e' Le ng th '(c m)' Viscosity'(Pa's)' Average'Length' 20"deg."slope," room"temp" 20"deg."slope," cold"room" 10"deg."slope," room"temp" 10"deg."slope," cold"room" 0" 0.05" 0.1" 0.15" 0.2" 0.25" 0.3" 0.35" 0" 0.2" 0.4" 0.6" 0.8" 1" 1.2" Av er ag e' Wid th /A ve ra ge 'L en gt h' Viscosity'(Pa's)' Average'Width/Average'Length' 20"deg."slope," room"temp" 20"deg."slope," cold"room" 10"deg."slope," room"temp" 10"deg."slope," cold"room" 
