PLANETARY MUSINGS

GEOL 512 and the Martian dichotomy boundary

This semester I am teaching a graduate seminar course centered around some unresolved problems regarding the history of the planet Mars.  The first topic is the origin of the hemispheric dichotomy.  Basically, the northern and southern hemispheres of Mars appear quite different.  The south is a few kilometers higher than the north, the north is smoother than the south, and the surface materials appear younger in the north than in the south.  The image below illustrates the basic idea - the colors are the topography of Mars from the MOLA instrument (a laser altimeter) and the blues in the north are low and the reds and oranges in the south are higher.  Several hypotheses have been put forth, ranging from one or multiple large impacts to internal processes like a past period of plate tectonics (Mars doesn't have plate tectonics today).  We are discussing the available data and how well various existing hypotheses work.  Students will be working on small individual projects related to the problem as well.  As sort of a catalog for myself and other students of Mars the following lists the papers we have been using to motivate our discussions so far.

Solomon, S. C., O. Aharonson, J. M. Aurnou, W. B. Banerdt, M. H. Carr, A. J. Dombard, H. V. Frey, M. P. Golombek, S. A. Hauck, II, J. W. Head, III, B. M. Jakosky, C. L. Johnson, P. J. McGovern, G. A. Neumann, R. J. Phillips, D. E. Smith, and M. T. Zuber, New perspectives on ancient Mars, Science, 307, 1214-1220, 2005.

Zuber, M. T., The crust and mantle of Mars, Nature, 412, 220-227, 2001.
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Nimmo, F., and K. Tanaka, Early crustal evolution of Mars, Annu. Rev. Earth Planet. Sci., 33, 133-161, 2005.

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McGill, G. E.,and S. W. Squyres, Origin of the Martian crustal dichotomy: Evaluating hypotheses, Icarus, 93, 386-393, 1991.

Fairén, A. G., and J. M. Dohm, Age and origin of the lowlands of Mars, Icarus, 168, 277-284,
2004.

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Frey, H. V., Impact constraints on, and a chronology for, major events in early Mars history, J. Geophys. Res., in press.

Neumann, G. A., M. T. Zuber, M. A. Wieczorek, P. J. McGovern, F. G. Lemoine, and D. E. Smith, Crustal structure of Mars from gravity and topography, J. Geophys. Res., 109,
08002, 2004.

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Connerney, J. E. P., M. H. Acuña, N. F. Ness, G. Kletetschka, D. L. Mitchell, R. P. Lin, and H. Reme, Tectonic implications of Mars crustal magnetism, Proc. Nat. Acad. Sci., 102, 14970-14975, 2005.

Lenardic, A., F. Nimmo, and L. Moresi, Growth of the hemispheric dichotomy and the cessation of plate tectonics on Mars, J. Geophys. Res., 109, E02003,
doi:10.1029/2003JE002172, 2004.

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Elkins-Tanton, L. T., P. Hess, and E. M. Parmentier, Possible formation of ancient crust on Mars through magma ocean processes, J. Geophys. Res., 110, E12S01,
doi:10.1029/2005JE002480, 2005

Zhong, S., and M. T. Zuber, Degree-1 mantle convection and the crustal dichotomy on Mars, Earth Planet. Sci. Lett., 189, 75-84, 2001.