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Mars North Polar Deposits: Stratigraphy, Age, and Geodynamical Response
Roger J. Phillips,1,2*Maria T. Zuber,3Suzanne E. Smrekar,4Michael T. Mellon,5James W. Head,6Kenneth L. Tanaka,7Nathaniel E. Putzig,1Sarah M. Milkovich,4Bruce A. Campbell,8Jeffrey J. Plaut,4Ali Safaeinili,4Roberto Seu,9Daniela Biccari,9Lynn M. Carter,8Giovanni Picardi,9Roberto Orosei,10P. Surdas Mohit,11,12Essam Heggy,13,14Richard W. Zurek,4Anthony F. Egan,1Emanuele Giacomoni,9Federica Russo,9Marco Cutigni,9Elena Pettinelli,15John W. Holt,16Carl J. Leuschen,17Lucia Marinangeli18
The Shallow Radar (SHARAD) on the Mars Reconnaissance Orbiterhas imaged the internal stratigraphy of the north polar layereddeposits of Mars. Radar reflections within the deposits reveala laterally continuous deposition of layers, which typicallyconsist of four packets of finely spaced reflectors separatedby homogeneous interpacket regions of nearly pure ice. The packet/interpacketstructure can be explained by approximately million-year periodicitiesin Mars' obliquity or orbital eccentricity. The observed 100-metermaximum deflection of the underlying substrate in response tothe ice load implies that the present-day thickness of an equilibriumelastic lithosphere is greater than 300 kilometers. Alternatively,the response to the load may be in a transient state controlledby mantle viscosity. Both scenarios probably require that Marshas a subchondritic abundance of heat-producing elements.
1 Southwest Research Institute, Boulder, CO 80302, USA. 2 Washington University, St. Louis, MO 63130, USA. 3 Massachusetts Institute of Technology, Cambridge, MA 02139–4307, USA. 4 Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA. 5 University of Colorado, Boulder, CO 80309–0392, USA. 6 Brown University, Providence, RI 02912, USA. 7 U.S. Geological Survey, Flagstaff, AZ 86001, USA. 8 Smithsonian Institution, Washington, DC 20013–7012, USA. 9 Dipartimento InfoCom, Università di Roma "La Sapienza," I-00184 Rome, Italy. 10 Istituto Nazionale di Astrofisica, I-00133 Rome, Italy. 11 Scripps Institution of Oceanography, La Jolla, CA 92093, USA. 12 University of British Columbia, Vancouver, British Columbia, Canada, V6T 1Z4. 13 Lunar and Planetary Institute, Houston, TX 77058, USA. 14 Institute de Physique du Globe de Paris, Paris, France. 15 Università Roma Tre, 00146 Rome, Italy. 16 Jackson School of Geosciences, University of Texas, Austin, TX 78712, USA. 17 University of Kansas, Lawrence, KS 66045–7612, USA. 18 Universita' d'Annunzio 65127 Pescara, Italy.
* To whom correspondence should be addressed. E-mail: roger{at}boulder.swri.edu
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|Abstract »|Full Text »|PDF »
100-meter maximum deflection of the underlying substrate in response to the ice load implies that the present-day thickness of an equilibrium elastic lithosphere is greater than 300 kilometers. Alternatively, the response to the load may be in a transient state controlled by mantle viscosity. Both scenarios probably require that Mars has a subchondritic abundance of heat-producing elements. 
