 MICROSTRUCTURE ON THE SURFACE OF DARK DUNES IN THE POLAR REGIONS OF MARS.  Bérczi Sz,1,2, Horváth A.1,3, Kereszturi A.1,4, Sik A.1,5, 1Collegium Budapest, H-1014 Budapest, Szentháromság u. 2. 2 Eötvös University, Inst. Physics, H-1117 Budapest, Pázmány 1/a., 3Konkoly Observatory, H-1121 Budapest, Konkoly-Thege M. u. 13. 4 Hungarian Astronomical Society, Budapest,  5 Eötvös University, Inst. Geology, Geography, H-1117 Budapest, Pázmány p. s. 1/c. Hungary,  (bercziszani@ludens.elte.hu)  detector [6], which is compatible with the idea of surface ice cover in the dark spots. On the basis of Phoenix in situ measurements and images, it was demonstrated that the fluid phase in form of brines may appeare on the surface [7] and this was supported by physical modeling, too [3, 8]. As a result liquid flows may be present in the analyzed features. Time sequence phases of DDS flows were observed at the South (Fig. 1.) and at the North (Fig. 2.) polar regions on the MGS MOC and MRO HiRISE images. Introduction: In this work we focus on the possible microscopic structures of the soil corresponding to the flow features originating from the Dark Dune Spots (DDSs), which have been studied in the last 10 years in the polar, seasonally frost covered regions of Mars [1, 2, 3]. In our earlier investigations on the MGS MOC images we discovered the DDS flow-features which were later identified as possible water or brine flows beginning to be formed during Martian springtime [4, 5].   Preliminary analysis of CRISM spectra from the target regions suggests that water ice is present as surface ice, or clouds between the dark surface and the  Observations and new results: In the last years several flow-like features  were observed on the slopes    Fig. 1. Southern hemisphere DDS-seepages extending on 80x100 m sized subsets of HiRISE  images of the Richardson crater. Image numbers and Ls-values from left: PSP-003175, 210.6°; PSP-003386, 220.7°; PSP-003597, 230.9°;  PSP-00374, 238.1° [9]. The slopes are tilted upward    Fig. 2. Gradually growing seepage-like features as the season passes by on 100x150 m HiRISE images taken in the Northern Polar Region t 77.5°N, 300.1°E (difference in days=22 and 12 terrestrial days respectively. Image numbers: PSP-007468, -007758 and -007903) [10]a  of polar dunes, em features formed by confined slope stre downslope with a s branching pattern "ponds" at their end Discussion: Pro types and location sections are visible microscopic brines dark front [12]. C) cover where the d visible. D) the graph affected  flow exten The ring structu be interpreted by geyser/fountain-like the erupted materia structure (it may c too) (Fig. 3.); or forced by various capillary effect, pre  Fig. 3. Appearance (84.7°N, 0.8°E Fig. 4.  Microscopic brine/water and ligh (68  of ring-strucrures during the seasonal development of a dark dune spot on the Northern Polar Region ,  in spring 2008). On these 450x300 m enlarged frames of HiRISE-images DDS can be seen [11]   models of various flow-structures of DDS-seepages described by soil-grain cross sections. Dark blue is t blue color shows frost. Lower left and central are 300x300 m enlarged frames of MRO HiRISE images .2°S, 1.32°E; numbers and Ls-values from left: PSP- 003432, 222.9°; PSP-003709, 236.4°).  Explanation given in the text anating from DDSs, different from  CO2-jets or wind blow [9]. These aks (DDS seepages) are moving peed of about 1 m/sol, showing a (Fig. 1., 2.) and accumulated .  posed microscopic view of various s of brine filled: different cross  in Fig. 4. A) the graph shows the only at the surface. B) extending the location of the retreating frost arker brine-wet surface becomes  shows the slope where the gravity ds downward. res visible around some DDS can two different models: 1) after a  eruption from the central portion l falls down forming the ring-like onsist of salts or refrosted vapors 2) a liquid material moves there  effects  beyond  gravity  (like  ssure from volume change or from  the liquid runnings after etc.) causing the flow to expand from the source [13] (Fig. 4.).  Acknowledgment: This work has been supported by the ESA ECS-project No. 98076.  References: [1] Szathmáry et al. (2007) in Planetary Systems and the Origin of Life, ed. Ralph Pudritz, Paul Higgs, Jonathan Stone, Cambridge Astrobiology Series III., Cambridge University Press, 241-262. [2] Horváth et al. (2009) Astrobiology 9/1, 90-103. [3] Kereszturi et al. (2009) Icarus 201, 492-503. [4] Horváth et al. (2001) 32th LPSC#1543. [5] Gánti el al. (2003) Origin of Life and Evolution of the Biosphere 33, 515-557. [6] Kereszturi et al. (2010), 41st  LPSC#1714. [7] Renno et al. (2009) JGR submitted. [8] Kereszturi at al. (2010) Icarus, doi:10.1016/j.icarus.2009.10.012. [9] Kereszturi et al. (2007) LPSC #1864, [10] Kereszturi et al. (2009) LPSC#1111. [11] Horváth et al. (2009) 32nd NIPR, Tokyo. [12] Möhlmann (2009) Icarus DOI: 10.1016/j.icarus.2009.11.013 [13] Möhlmann (2010), submitted to Icarus. 
