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Turbulence and Aeolian Morphodynamics in Craters on Mars: Application to Gale Crater, Landing Site of the Curiosity Rover

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Turbulence and Aeolian Morphodynamics in Craters on Mars: Application to Gale Crater, Landing Site of the Curiosity Rover 16TH EUROPEAN TURBULENCE CONFERENCE, 21-24 AUGUST, 2017, STOCKHOLM,SWEDEN TURBULENCE AND AEOLIAN MORPHODYNAMICS IN CRATERS ON MARS: APPLICATION TO GALE CRATER, LANDING SITE OF THE CURIOSITY ROVER William Anderson1, Gary Kocurek2 & Kenzie Day2 1Mechanical Engineering Dept., Univ. Texas at Dallas, Richardson, Texas, USA 2Dept. Geological Sciences, Jackson School of Geosciences, Univ. Texas at Austin, Austin, Texas, USA Mars is a dry planet with a thin atmosphere. Aeolian processes – wind-driven mobilization of sediment and dust – are the dominant mode of landscape variability on the dessicated landscapes of Mars. Craters are common topographic features on the surface of Mars, and many craters on Mars contain a prominent central mound (NASA’s Curiosity rover was landed in Gale crater, shown in Figure 1a [1], while Figures 1b and 1c show Henry and Korolev crater, respectively). These mounds are composed of sedimentary fill and, therefore, they contain rich information on the evolution of climatic conditions on Mars embodied in the stratigraphic “layering” of sediments. Many other craters no longer house a mound, but contain sediment and dust from which dune fields and other features form (see, for example, Victoria Crater, Figure 1d). Using density-normalized large-eddy simulations, we have modeled turbulent flows over crater-like topographies that feature a central mound. Resultant datasets suggest a deflationary mechanism wherein vortices shed from the upwind crater rim are realigned to conform to the crater profile via stretching and tilting. This was accomplished using three- dimensional datasets (momentum and vorticity) retrieved from LES. As a result, helical vortices occupy the inner region of the crater and, therefore, are primarily responsible for aeolian morphodynamics in the crater (radial katabatic flows are also important to aeolian processes within the crater [2]). Figure 1(e-f) shows contours of terms in the Reynolds-averaged mean streamwise vorticity transport equation (e: stretching; f and g: tilting of spanwise and vertical vorticity, respectively, and h: production by turbulent stresses), along with contours of mean streamwise vorticity. These contours highlight the role of mean spatial gradients in sustaining the mean secondary flows. (a) (b) (c) (d) D = 120 km D = 150 km (b) D = 147 km (e) (f) (g) (h) Figure 1. Illustration of Mars craters and turbulent flow statistics. Panel (a): Gale Crater, Mars; Panel (b): Henry Crater, Mars; Panel (c): Korolev Crater, Mars; Panel (d): Victoria Crater, Mars (Source: NASA). Panels (e-h) show turbulent flow statistics from flow over synthetic craters: (e) stretching of mean streamwise vorticity; (f) and (g) show tilting of spanwise and vertical vorticity into the streamwise direction, respectively; Panel (h) shows production of mean streamwise vorticity by turbulent torque. Orange and blue solid contours correspond with positive and negative mean streamwise vorticity, respectively. References [1] J.P. Grotzinger, S. Gupta, M.C. Malin, D.M. Rubin, J. Schieber, K. Siebach, D.Y. Sumner, K. Stack, A.R. Vasavada, R.E. Arvidson, F. Calef III, L. Edgar, W.F. Fischer, J.A. Grant, J. Griffes, L.C. Kah, M.P. Lamb, K.W. Lewis, N. Magnold, M.E. Minitti, M. Palucis, M. Rice, R.M.E. Williams, R.A. Yingst, D. Blake, D. Blaney, P. Conrad, J. Crisp, W.E. Dietrich, G. Dromart, K.S. Edgett, R.C. Ewing, R. Gellert, J.A. Hurowitz, G. Kocurek, P. Mahaffy, M.J. McBride, S.M. McLennan, M. Mischna, D. Ming, R. Milliken, H. Newsom, D. Oehler, T.J. Parker, D. Vaniman, R.C. Wiens, and S.A. Wilson. Deposition, exhumation, and paleoclimate of an ancient lake deposit, Gale crater, Mars. Science, 350:doi:6257/aac7575âA¸S8⢠A¸S15,˘ 2015. [2] E.S. Kite, J. Sneed, D.P. Mayer, K.W. Lewis, T.I. Michaels, A. Hore, and S.C.R. Rafkin. Evolution of major sedimentary mounds on mars: buildup via anticompensational stacking modulated by climate change. Journal of Geophysical Research: Planets, 121:2282–2324, 2016..
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