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Martian dichotomy

The most conspicuous feature of Mars is a sharp contrast, known as the Martian dichotomy, between the Southern and the Northern hemispheres. The two hemispheres' geography differ in elevation by 1 to 3 km. The average thickness of the Martian crust is 45 km, with 32 km in the northern lowlands region, and 58 km in the southern highlands.

The boundary between the two regions is quite complex in places. One distinctive type of topography is called fretted terrain.[1][2][3] It contains mesas, knobs, and flat-floored valleys having walls about a mile high. Around many of the mesas and knobs are lobate debris aprons that have been shown to be rock glaciers.[4][5][6][7]

Many large valleys formed by the lava erupted from the volcanoes of Mars cut through the dichotomy.[8][9][10][11]

The Martian dichotomy boundary includes the regions called Deuteronilus Mensae, Protonilus Mensae, and Nilosyrtis Mensae. All three regions have been studied extensively because they contain landforms believed to have been produced by the movement of ice[12][13] or paleoshorelines questioned as formed by volcanic erosion.[14] In the Terra Cimmeria–Nepenthes Mensae transitional zone, the dichotomy boundary is characterized by an escarpment with a local relief of about 2 km, and interconnected NW-SE-trending closed depressions at the foot of the dichotomy probably related to extensional tectonics.[15]

The northern lowlands comprise about one-third of the surface of Mars and are relatively flat, with as many impact craters as the southern hemisphere.[16] The other two-thirds of the Martian surface are the highlands of the southern hemisphere. The difference in elevation between the hemispheres is dramatic. Three major hypotheses have been proposed for the origin of the crustal dichotomy: endogenic (by mantle processes), single impact, or multiple impact. Both impact-related hypotheses involve processes that could have occurred before the end of the primordial bombardment, implying that the crustal dichotomy has its origins early in the history of Mars.

  1. ^ Greeley, R. and J. Guest. 1987. Geological map of the eastern equatorial region of Mars, scale 1:15,000,000. U. S. Geol. Ser. Misc. Invest. Map I-802-B, Reston, Virginia
  2. ^ Sharp, R (1973). "Mars Fretted and chaotic terrains" (PDF). J. Geophys. Res. 78 (20): 4073–4083. Bibcode:1973JGR....78.4073S. doi:10.1029/jb078i020p04073.
  3. ^ Whitten, Dorothea S. (1993). Imagery & Creativity: Ethnoaesthetics and Art Worlds in the Americas. ISBN 978-0-8165-1247-8.
  4. ^ Plaut, J. et al. 2008. Radar Evidence for Ice in Lobate Debris Aprons in the Mid-Northern Latitudes of Mars. Lunar and Planetary Science XXXIX. 2290.pdf
  5. ^ Carr, M. 2006. The Surface of Mars. Cambridge University Press. ISBN 978-0-521-87201-0
  6. ^ Squyres, S (1978). "Martian fretted terrain: Flow of erosional debris". Icarus. 34 (3): 600–613. Bibcode:1978Icar...34..600S. doi:10.1016/0019-1035(78)90048-9.
  7. ^ Kieffer, Hugh H. (October 1992). Mars: Maps. ISBN 978-0-8165-1257-7.
  8. ^ Leone, Giovanni (2014-05-01). "A network of lava tubes as the origin of Labyrinthus Noctis and Valles Marineris on Mars". Journal of Volcanology and Geothermal Research. 277: 1–8. Bibcode:2014JVGR..277....1L. doi:10.1016/j.jvolgeores.2014.01.011.
  9. ^ Leverington, David W. (2004-10-01). "Volcanic rilles, streamlined islands, and the origin of outflow channels on Mars". Journal of Geophysical Research: Planets. 109 (E10): E10011. Bibcode:2004JGRE..10910011L. doi:10.1029/2004JE002311. ISSN 2156-2202.
  10. ^ Leverington, David W. (2011-09-15). "A volcanic origin for the outflow channels of Mars: Key evidence and major implications". Geomorphology. 132 (3–4): 51–75. Bibcode:2011Geomo.132...51L. doi:10.1016/j.geomorph.2011.05.022. S2CID 26520111.
  11. ^ Leone, Giovanni (2016-01-01). "Alignments of volcanic features in the southern hemisphere of Mars produced by migrating mantle plumes". Journal of Volcanology and Geothermal Research. 309: 78–95. Bibcode:2016JVGR..309...78L. doi:10.1016/j.jvolgeores.2015.10.028.
  12. ^ Baker, D.; et al. (2010). "Flow patterns of lobate debris aprons and lineated valley fill north of Ismeniae Fossae, Mars: Evidence for extensive mid-latitude glaciation in the Late Amazonian". Icarus. 207 (1): 186–209. Bibcode:2010Icar..207..186B. doi:10.1016/j.icarus.2009.11.017.
  13. ^ "HiRISE - Glacier? (ESP_018857_2225)". www.uahirise.org. Archived from the original on 2017-05-30.
  14. ^ Hargitai, Henrik; Kereszturi, Ákos (2015). Encyclopedia of Planetary Landforms - Springer. doi:10.1007/978-1-4614-3134-3. ISBN 978-1-4614-3133-6. S2CID 132406061.
  15. ^ García-Arnay, Ángel (2023). "Geologic map of the Terra Cimmeria-Nepenthes Mensae transitional zone, Mars – 1:1.45Million". Journal of Maps. 19 (1). doi:10.1080/17445647.2023.2227205.
  16. ^ Frey, H. V. (2006-08-01). "Impact constraints on, and a chronology for, major events in early Mars history". Journal of Geophysical Research: Planets. 111 (E8): E08S91. Bibcode:2006JGRE..111.8S91F. doi:10.1029/2005JE002449. ISSN 2156-2202.

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