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Concentric crater fill

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Concentric crater fill

A concentric crater fill is a landform where the floor of a crater is mostly covered with a large number of parallel ridges.[1] It is common in the mid-latitudes of Mars,[2][3] and is widely believed to be caused by glacial movement.[4][5] Areas on Mars called Deuteronilus Mensae and Protonilus Mensae contain many examples of concentric crater fill.

Description

Concentric crater fill, like lobate debris aprons and lineated valley fill, is believed to be ice-rich.[6] Based on accurate topography measures of height at different points in these craters and calculations of how deep the craters should be based on their diameters, it is thought that the craters are 80% filled with mostly ice.[7][8][9][10] That is, they hold hundreds of meters of material that probably consists of ice with a few tens of meters of surface debris.[11][12] The ice accumulated in the crater from snowfall in previous climates.[13][14][15] Recent modeling suggests that concentric crater fill develops over many cycles in which snow is deposited, then moves into the crater. Once inside the crater shade and dust preserve the snow. The snow changes to ice. The many concentric lines are created by the many cycles of snow accumulation. Generally snow accumulates whenever the axial tilt reaches 35 degrees.[16]

Sometimes boulders are found on concentric crater fill; it is believed they fell off the crater wall, then were transported away from the wall with the movement of the glacier.[17][18] Erratics on Earth were carried by similar means.

High resolution pictures taken with HiRISE reveal that some of the surfaces of concentric crater fill are covered with strange patterns called closed-cell and open-cell brain terrain. The terrain resembles a human brain. It is believed to be caused by cracks in the surface accumulating dust and other debris, together with ice sublimating from some of the surfaces. The cracks are the result stress from gravity and seasonal heating and cooling.[19][20]

See also

References

  1. ^ http://hiroc.lpl.arizona.edu/images/PSP/diafotizo.php?ID=PSP_111926_2185
  2. ^ Dickson, J. et al. 2009. Kilometer-thick ice accumulation and glaciation in the northern mid-latitudes of Mars: Evidence for crater-filling events in the Late Amazonian at the Phlegra Montes. Earth and Planetary Science Letters.
  3. ^ http://hirise.lpl.arizona.edu/PSP_001926_2185
  4. ^ Head, J. et al. 2006. Extensive valley glacier deposits in the northern mid-latitudes of Mars: Evidence for late Amazonian obliquity-driven climate change. Earth Planet. Sci Lett: 241. 663-671.
  5. ^ Levy, J. et al. 2007. Lineated valley fill and lobate debris apron stratigraphy in Nilosyrtis Mensae, Mars: Evidence for phases of glacial modification of the dichotomy boundary. J. Geophys. Res: 112.
  6. ^ Levy, J. et al. 2009. Concentric crater fill in Utopia Planitia: History and interaction between glacial "brain terrain" and periglacial processes. Icarus: 202. 462-476.
  7. ^ Levy, J., J. Head, D. Marchant. 2010. Concentric Crater fill in the northern mid-latitudes of Mars: Formation process and relationships to similar landforms of glacial origin. Icarus 2009, 390-404.
  8. ^ Levy, J., J. Head, J. Dickson, C. Fassett, G. Morgan, S. Schon. 2010. Identification of gully debris flow deposits in Protonilus Mensae, Mars: Characterization of a water-bearing, energetic gully-forming process. Earth Planet. Sci. Lett. 294, 368–377.
  9. ^ http://hirise.lpl.arizona.edu/ESP_032569_2225
  10. ^ Garvin, J., S. Sakimoto, J. Frawley. 2003. Craters on Mars: Geometric properties from gridded MOLA topography. In: Sixth International Conference on Mars. July 20–25 2003, Pasadena, California. Abstract 3277.
  11. ^ Garvin, J. et al. 2002. Global geometric properties of martian impact craters. Lunar Planet. Sci: 33. Abstract # 1255.
  12. ^ http://photojournal.jpl.nasa.gov/catalog/PIA09662
  13. ^ Kreslavsky, M. and J. Head. 2006. Modification of impact craters in the northern planes of Mars: Implications for the Amazonian climate history. Meteorit. Planet. Sci.: 41. 1633-1646
  14. ^ Madeleine, J. et al. 2007. Exploring the northern mid-latitude glaciation with a general circulation model. In: Seventh International Conference on Mars. Abstract 3096.
  15. ^ http://hirise.lpl.arizona.edu/PSP_002917_2175
  16. ^ Fastook, J., J.Head. 2014. Concentric crater fill: Rates of glacial accumulation, infilling and deglaciation in the Amazonian and Noachian of Mars. 45th Lunar and Planetary Science Conference (2014) 1227.pdf
  17. ^ Marchant, D. et al. 2002. Formation of patterned ground and sublimation till over Miocene glacier ice in Beacon valley, southern Victorialand, Antarctica. Geol. Soc. Am. Bull:114. 718-730.
  18. ^ Head, J. and D. Marchant. 2006. Modification of the walls of a Noachian crater in northern Arabia Terra (24E, 39N) during mid-latitude Amazonian glacial epochs on Mars: Nature and evolution of lobate debris aprons and their relationships to lineated valley fill and glacial systems. Lunar Planet. Sci: 37. Abstract # 1126.
  19. ^ Mellon, M. 1997. Small-scale polygonal features on Mars: Seasonal thermal contraction cracks in permafrost. J. Geophysical Res: 102. 25,617-625,628.
  20. ^ Ley, J. et al. 2009. Concentric crater fill in Utopia Planitia: History and interaction between glacial "brain terrain" and periglacial processes. Icarus: 202. 462-476.
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