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2009 Portland GSA Annual Meeting (18-21 October 2009)

Paper No. 1
Presentation Time: 8:00 AM

RADAR SOUNDING OF THE POLAR LAYERED DEPOSITS ON MARS


PHILLIPS, Roger J.1, PUTZIG, Nathaniel E.2, CAMPBELL, Bruce A.3, PLAUT, Jeffrey J.4, EGAN, Anthony F.5, CARTER, Lynn M.3, HOLT, John W.6, SMREKAR, Suzanne E.4, HEAD, James W.7 and SEU, Roberto8, (1)Planetary Science Directorate, Southwest Research Institute, 1050 Walnut St, Suite 300, Boulder, CO 80302, (2)Department of Space Studies, Southwest Research Institute, 1050 Walnut Street, Suite 300, Boulder, CO 80402, (3)Center for Earth and Planetary Studies, Smithsonian Institution, MRC 315, PO Box 37012, Washington, DC 20013-7012, (4)Jet Propulsion Laboratory, California Institute of Technology, Mail Stop 183-501, 4800 Oak Grove Dr, Pasadena, CA 91109, (5)Department of Space Operations, Southwest Research Institute, 1050 Walnut Street, Suite 300, Boulder, CO 80402, (6)Institute for Geophysics, Jackson School of Geosciences, University of Texas at Austin, J.J. Pickle Research Campus, Bldg. 196, 10100 Burnet Road, Austin, TX 78758-4445, (7)Department of Earth, Environmental and Planetary Sciences, Brown University, Providence, RI 02912, (8)InfoCom, University of Rome La Sapienza, Rome, 18-00184, Italy, roger@boulder.swri.edu

For the past several years there have been two sounding radars in orbit around Mars. One is MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding) on the Mars Express orbiter and the other is SHARAD (Shallow Radar) on the Mars Reconnaissance Orbiter. SHARAD is designed to study dielectric contrasts associated with geologic layering on fine (10 m) vertical scales and to typically sub-km depths. SHARAD complements the spatially coarse but deeper sounding of the lower-frequency MARSIS. The depth of exploration of these radars is controlled by the loss properties of the material that the radar waves pass through, with the result that ice-rich material is the most fruitful target for sounding. The radars have mapped the internal structure of the layered deposits at both poles, revealing details of the layering not observable from surface exposures and showing that the layered deposits are dominated by ice. The North Polar Layered Deposits (NPLD) are draped over the Basal Unit, which exists under the main lobe of the northern polar cap. Within the NPLD, two vertical scales of reflection spacing that appear as a packet/interpacket structure are widespread, suggesting the involvement of two different periodicities of climate forcing. A packet/interpacket structure is seen distinctly only in the Promethei Lingula region of the South Polar Layered deposits (SPLD). Beneath the sloping plateau of the SPLD (centered roughly on 180°E) the layering is not as distinct, and near the highest elevation of the SPLD (Australe Mensa) layering is virtually absent. Overall, the internal radar structure seems to support the three major stratigraphic divisions proposed by Milkovich and Plaut (2008) for the SPLD. An unexpected result for both the NPLD and SPLD is that the substrates beneath deflect very little in response to the ice loads. This implies that the elastic lithosphere at the poles is very thick, or the load is not in equilibrium with the viscous mantle, or that martian heat flow has significant spatial variations.

Session No. 20

T93. Glacial Mars
Sunday, 18 October 2009: 8:00 AM-12:00 PM
A106 (Oregon Convention Center)
Geological Society of America Abstracts with Programs. Vol. 41, No. 7, p.68
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