Concentric crater fill

Concentric crater fill is when 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, and is widely believed to be caused by glacial movement. Areas on Mars called Deuteronilus Mensae and Protonilus Mensae contain many examples of concentric crater fill.

Description

Concentric crater fill is common in the mid-latitudes of Mars.^{[2] [3]}It is thought to be a result of glacial movement.^{[4] [5]} Sometimes boulders are found on concentric crater fill; it is believed they fell off crater wall, then were transported away from the wall with the movement of the glacier.^[6][7]Erratics on Earth were carried by similar means. 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. That is, they hold hundreds of meters of material that probably consists of ice with a few tens of meters of surface debris.^{[8] [9]} The ice accumulated in the crater from snowfall in previous climates.^{[10] [11] [12]} Concentric crater fill, like Lobate debris aprons, and Lineated valley fill are believed to be ice-rich features. ^[13]

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.^[14][15]

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  Wide-view of concentric crater fill, as seen by HiRISE. Location is the Casius quadrangle.

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  Concentric Crater Fill Close-up of near the top of previous image, as seen by HiRISE. The surface debris covers water ice. Location is the Casius quadrangle.

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  Well-developed hollows, as seen by HiRISE under the HiWish program. Location is the Casius quadrangle.

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  Close-up that shows cracks containing pits on the floor of a crater containing concentric crater fill, as seen by HiRISE under HiWish program. Location is the Casius quadrangle.

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  Close-up that shows cracks containing pits on the floor of a crater, as seen by HiRISE under HiWish program. Cracks may start as a line of pits that enlarge, then join. Location is the Casius quadrangle.

See also

• Climate of Mars
• Water on Mars
• Fretted terrain
• Impact crater
• Deuteronilus Mensae
• Protonilus Mensae
• Glacier
• Casius quadrangle
• Glaciers on Mars

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. ^ 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.
7. ^ 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.
8. ^ Garvin, J. et al. 2002. Global geometric properties of martian impact craters. Lunar Planet. Sci: 33. Abstract # 1255.
9. ^ http://photojournal.jpl.nasa.gov/catalog/PIA09662
10. ^ 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
11. ^ Madeleine, J. et al. 2007. Exploring the northern mid-latitude glaciation with a general circulation model. In: Seventh International Conference on Mars. Abstract 3096.
12. ^ http://hirise.lpl.arizona.edu/PSP_002917_2175
13. ^ 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.
14. ^ Mellon, M. 1997. Small-scale polygonal features on Mars: Seasonal thermal contraction cracks in permafrost. J. Geophysical Res: 102. 25,617-625,628.
15. ^ 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.