Scalloped depressions and small-sized polygons in western Utopia Planitia,Mars: A new formation hypothesis |
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| Authors: | A. Séjourné F. Costard J. Gargani R.J. Soare A. Fedorov C. Marmo |
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| Affiliation: | 1. Université Paris-Sud XI, CNRS, Laboratoire IDES, UMR 8148, 91405 Orsay, France;2. Dawson College, Department of Geography, Montreal, Canada;3. Permafrost Institute, Russian Academy of Sciences, Yakutsk, Russia;1. U.S. Geological Survey, Astrogeology Science Center, 2255 N. Gemini Drive, Flagstaff, AZ 86001, USA;2. University of Colorado, Boulder, CO, USA;1. V.I. Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, 19, Kosygin St., 119991 Moscow, Russia;2. Institut für Planetologie, Westfälische Wilhelms-Universität, Münster, Wilhelm-Klemm-Str. 10, 48149 Münster, Germany;1. Physikalisches Institut, Bern Univeristät, Sidlerstrasse, 5, 3012 Berne, Switzerland;2. Whitin Observatory, Department of Astronomy, Wellesley College, Wellesley, MA, 02481, USA;3. Department of Physical Sciences, MacEwan University, Edmonton, Alberta, Canada;4. Institut d’Astrophysique Spatiale, Paris-Sud University, Orsay, France;5. Planetary Science Institute, Tucson, AZ, 85719, USA;6. NASA Ames Research Center, Mountain View, CA, 94035, USA;7. SETI Institute, Mountain View, CA 94043, USA;1. Nordic Volcanological Center, Institute of Earth Sciences, University of Iceland, Sturlugata 7, 101 Reykjavssík, Iceland;2. Department of Earth Sciences, University of Aarhus, Hoegh-Guldberggade 2, 8000 Aarhus C, Denmark |
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| Abstract: | Flat-floored depressions with scalloped-shapes and spatially associated small-sized polygons (diameter <～100 m) dot the landscape of western Utopia Planitia (centered at 45°N–95°E). The scalloped depressions are thought to be the result of ice-rich regolith undergoing degradation by sublimation or thaw. Current models suggest that the formation and development of the depressions occur in a poleward direction due to the enhanced sublimation of their equator-facing slopes. By contrast, we propose a conceptual model that shows the equatorward growth of depressions due to preferential degradation by sublimation of their pole-facing slopes. Our model is based on a geomorphological study of the depressions and small-sized polygons in western Utopia Planitia (80°–110°E, 35°–50°N), using images from the High Resolution Imaging Science Experiment (HiRISE) and topographical data from the Mars Orbiter Laser Altimeter (MOLA) and a HiRISE stereo Digital Elevation Model (DEM). Here we describe (i) a morphological evolution of small-sized polygons within the depressions, from low-centered to high-centered, that facilitates one's understanding of depression growth and development; and (ii) occurrence of v-shaped alcoves, failure cracks and semicircular hollows that point to a retrogressive degradation of the pole-facing slopes of depressions. We propose that the development of the depressions is due to heightened insolation of their pole-facing slopes, leading to enhanced sublimation of ground-ice. Based upon the inferred asymmetric insolation, we suggest that the equatorward expansion of depressions occurred during recent high-obliquity periods of Mars. |
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