Submitted on March 10, 2008
Accepted on May 7, 2008

Mars North Polar Deposits: Stratigraphy, Age, and Geodynamical Response

¹ Southwest Research Institute, Boulder, CO 80302, USA.; Washington University, St. Louis, MO 63130, USA.
² Massachusetts Institute of Technology, Cambridge, MA 02139-4307, USA.
³ Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA.
⁴ University of Colorado, Boulder, CO 80309-0392, USA.
⁵ Brown University, Providence, RI 02912, USA.
⁶ U.S. Geological Survey, Flagstaff, AZ 86001, USA.
⁷ Southwest Research Institute, Boulder, CO 80302, 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 & University of British Columbia, Vancouver, BC, Canada, V6T 1Z4.
¹² Lunar and Planetary Institute, Houston, TX, 77058, USA & Institute de Physique du Globe de Paris, Paris, France.
¹³ Università Roma Tre, 00146 Rome, Italy.
¹⁴ Jackson School of Geosciences, University of Texas, Austin, TX 78712, USA.
¹⁵ University of Kansas, Lawrence, KS 66045-7612.
¹⁶ Universita' d'Annunzio 65127 Pescara, Italy.

^* To whom correspondence should be addressed.
Roger J. Phillips , E-mail: roger{at}boulder.swri.edu

The sounding radar SHARAD on the Mars Reconnaissance Orbiter has imaged the internal stratigraphy of the North Polar Layered Deposits of Mars. Radar reflections within the deposits reveal laterally-continuous deposition of layers, which consist typically of four packets of finely-spaced reflectors separated by homogeneous inter-packet regions of nearly pure ice. The packet/inter-packet structure can be explained by likely ~million-year periodicities in Mars’ obliquity or orbital eccentricity. The observed ~100-m 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 km. Alternatively, the response to the load may be in a transient state controlled by mantle viscosity. Both scenarios likely require that Mars has a sub-chondritic abundance of heat-producing elements.