Subsurface structure of Planum Boreum from Mars Reconnaissance Orbiter Shallow Radar soundings

Abstract We map the subsurface structure of Planum Boreum using sounding data from the Shallow Radar (SHARAD) instrument onboard the Mars Reconnaissance Orbiter. Radar coverage throughout the 1,000,000-km2 area reveals widespread reflections from basal and internal interfaces of the north polar layered deposits (NPLD). A dome-shaped zone of diffuse reflectivity up to 12 μs (∼1-km thick) underlies two-thirds of the NPLD, predominantly in the main lobe but also extending into the Gemina Lingula lobe across Chasma Boreale. We equate this zone with a basal unit identified in image data as Amazonian sand-rich layered deposits [Byrne, S., Murray, B.C., 2002. J. Geophys. Res. 107, 5044, 12 pp. doi:10.1029/2001JE001615; Fishbaugh, K.E., Head, J.W., 2005. Icarus 174, 444–474; Tanaka, K.L., Rodriguez, J.A.P., Skinner, J.A., Bourke, M.C., Fortezzo, C.M., Herkenhoff, K.E., Kolb, E.J., Okubo, C.H., 2008. Icarus 196, 318–358]. Elsewhere, the NPLD base is remarkably flat-lying and co-planar with the exposed surface of the surrounding Vastitas Borealis materials. Within the NPLD, we delineate and map four units based on the radar-layer packets of Phillips et al. [Phillips, R.J., and 26 colleagues, 2008. Science 320, 1182–1185] that extend throughout the deposits and a fifth unit confined to eastern Gemina Lingula. We estimate the volume of each internal unit and of the entire NPLD stack (821,000 km3), exclusive of the basal unit. Correlation of these units to models of insolation cycles and polar deposition [Laskar, J., Levrard, B., Mustard, J.F., 2002. Nature 419, 375–377; Levrard, B., Forget, F., Montmessin, F., Laskar, J., 2007. J. Geophys. Res. 112, E06012, 18 pp. doi:10.1029/2006JE002772] is consistent with the 4.2-Ma age of the oldest preserved NPLD obtained by Levrard et al. [Levrard, B., Forget, F., Montmessin, F., Laskar, J., 2007. J. Geophys. Res. 112, E06012, 18 pp. doi:10.1029/2006JE002772]. We suggest a dominant layering mechanism of dust–content variation during accumulation rather than one of lag production during periods of sublimation.

[1]  P. P. del Marmo,et al.  Accumulation and Erosion of Mars' South Polar Layered Deposits , 2007, Science.

[2]  D. H. Scott,et al.  Geologic map of the polar regions of Mars , 1987 .

[3]  Kenneth L. Tanaka.  Geology and insolation-driven climatic history of Amazonian north polar materials on Mars , 2005, Nature.

[4]  G. P. Johari.  The dielectric properties of H2O and D2O ice Ih at MHz frequencies , 1976 .

[5]  Roberto Orosei,et al.  Mars North Polar Deposits: Stratigraphy, Age, and Geodynamical Response , 2008, Science.

[6]  J. Laskar,et al.  Orbital forcing of the martian polar layered deposits , 2002, Nature.

[7]  C. Mätzler,et al.  ERRATUM: Dielectric properties of fresh-water ice at microwave frequencies , 1987 .

[8]  Roger J. Phillips,et al.  Radar subsurface mapping of the polar layered deposits on Mars , 2006 .

[9]  B. Murray,et al.  North polar stratigraphy and the paleo-erg of Mars , 2001 .

[10]  Robert M. Haberle,et al.  Orbital change experiments with a Mars general circulation model , 2003 .

[11]  Chris H. Okubo,et al.  North polar region of Mars: Advances in stratigraphy, structure, and erosional modification , 2008 .

[12]  Alessandro Frigeri,et al.  Radar evidence for ice in lobate debris aprons in the mid‐northern latitudes of Mars , 2009 .

[13]  A. McEwen,et al.  Meter-Scale Morphology of the North Polar Region of Mars , 2007, Science.

[14]  P. Huybers,et al.  Is there an orbital signal in the polar layered deposits on Mars , 2009 .

[15]  M. E. Peters,et al.  Echo source discrimination in single-pass airborne radar sounding data from the Dry Valleys, Antarctica: Implications for orbital sounding of Mars , 2006 .

[16]  Kenneth L. Tanaka,et al.  Accumulation and erosion of south polar layered deposits in the Promethei Lingula region, Planum Australe, Mars , 2006 .

[17]  James W. Head,et al.  North polar cap of Mars: Polar layered deposit characterization and identification of a fundamental climate signal , 2005 .

[18]  Jacques Laskar,et al.  Long term evolution and chaotic diffusion of the insolation quantities of Mars , 2004 .

[19]  R. Phillips,et al.  SHARAD sounding radar on the Mars Reconnaissance Orbiter , 2007 .

[20]  Roberto Orosei,et al.  Radar Soundings of the Subsurface of Mars , 2005, Science.

[21]  Jeffrey J. Plaut,et al.  Surface Ages and Resurfacing Rates of the Polar Layered Deposits on Mars , 2000 .

[22]  James W. Head,et al.  Origin and characteristics of the Mars north polar basal unit and implications for polar geologic history , 2005 .

[23]  Roberto Orosei,et al.  Subsurface Radar Sounding of the South Polar Layered Deposits of Mars , 2007, Science.

[24]  Ali Safaeinili,et al.  Radar Sounding Evidence for Buried Glaciers in the Southern Mid-Latitudes of Mars , 2008, Science.

[25]  Wlodek Kofman,et al.  North polar deposits of Mars: Extreme purity of the water ice , 2009 .

[26]  David E. Smith,et al.  Mars Orbiter Laser Altimeter: Experiment summary after the first year of global mapping of Mars , 2001 .

[27]  O. Aharonson,et al.  Structure of the basal unit of the North Polar Plateau of Mars, from MARSIS , 2009, 2009 IEEE Radar Conference.

[28]  R. Phillips,et al.  Stratigraphy of Promethei Lingula, south polar layered deposits, Mars, in radar and imaging data sets , 2009 .

[29]  R. Jacobel,et al.  Analysis of deep‐penetrating radar surveys of West Antarctica, US‐ITASE 2001 , 2003 .

[30]  J. Burns,et al.  The astronomical theory of climatic change on Mars , 1980 .

[31]  F Forget,et al.  The state and future of Mars polar science and exploration. , 2000, Icarus.

[32]  Jacques Laskar,et al.  Recent formation and evolution of northern Martian polar layered deposits as inferred from a Global Climate Model , 2007 .

[33]  E. Steig,et al.  Ice Age storm trajectories inferred from radar stratigraphy at Taylor Dome, Antarctica , 1998 .