Basal Topography of the South Polar Layered Deposits

Details Basal Topography of the South Polar Layered Deposits Basal Topography of the South Polar Layered Deposits

Dec 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agufm.p13a0971d&link_type=abstract

American Geophysical Union, Fall Meeting 2004, abstract #P13A-0971

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5462 Polar Regions, 6225 Mars

Scientific paper

The ice inferred to comprise the south polar layered deposits (SPLD) represents a significant fraction of the total water reservoir of the planet. The basal topography of these deposits is currently unconstrained but may be expected to contain considerable relief based on the heavily cratered nature of the surrounding terrain. In this work we report on our efforts to characterize the overall nature of this basal topography and in so doing better constrain the volume of this important volatile reservoir. Our approach has been to measure elevations at the periphery of the SPLD (defined by [1]) and use various interpolation techniques to estimate the basal topography. We used 1300 control points from the edges and areas surrounding the SPLD and included extensive control points from within the Chasmae and other features to fit a surface beneath the SPLD. No assumptions were made about any lithospheric flexure, nor did the results suggest that possibility. We first tested a variety of surface interpolation routines on a comparable area of cratered terrain immediately adjacent to the SPLD, using the same spatial distribution of 1300 height control points as we used for the SPLD itself, and found that the topography was broadly reproducible (ignoring craters) to within a few hundred meters. The SPLD basal topography we derive can be subtracted from the current spatial topography to produce isopach maps of the layered deposits. All interpolation methods we tested (within the ArcMap 8.3) indicate a lower total SPLD volume than that previous published [Smith et al., 2001]. Our best estimate for the SPLD volume is ~1 million km3, with a formal error in volume of ~5%, corresponding to an average thickness of ~950 meters. In comparison, [2] estimated this volume to be ~1.2-1.7 million km3. The Prometheus impact basin is present as a rimmed depression, consistent with the inference by [3]. More unexpected is the presence of a broad ridge underlying nearly the entire eastern half of the SPLD, which makes those deposits relatively thin. Our isopach maps show the northwestern portion of the Ultimi lobe to be an isolated thick region, in agreement with [1]. [1] Kolb, E. J., and K. L. Tanaka (2001), Icarus, 154, 22-39. [2] Smith, D. E., et al. (2001), J. Geophys. Res., 106(E10), 23,689-23,722. [3] Byrne, S., and A. B. Ivanov (2004), J. Geophys. Res., In press.

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