HR: 0800h
AN: P31B-0203    [Abstracts]
TI: Evolution of the North Polar Cap of Mars
AU: * Hecht, M H
EM: michael.h.hecht@jpl.nasa.gov
AF: Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr., M/S 302-231, Pasadena, CA 91109 United States
AB: While the rate of accumulation or ablation of the polar cap is uncertain to 3 orders of magnitude (e.g. Laskar et al., Nature 419, 2002), there is wide agreement that orbital forcing, as manifested in the visible layering of the PLD, drives variations on the scale of tens of thousands to millions of years. The very fact that we can see the PLD striations implies that we are not in a period of aggressive accumulation, which would obscure them. Morphological structures, notably Chasma Boreale, also suggest that the shape of the polar cap evolves despite the lack of evidence for bulk flow. Morphological evolution of a volatile material in a radiative environment is strongly geometry-dependent, and therefore a model of ablation should self-consistently incorporate the equilibrium shape of the ablating structures. In this work, both vertical slope and horizontal curvature of ablating scarps are considered in a model of radiative balance, orbital forcing, and heat storage in ice. Two conclusions leap from the results: (1) Scarp retreat is sufficient to explain the evolution of the cap on the scale of a few million years, and (2) Precession of perihelion is the dominant forcing term, while obliquity change primarily influences the equilibrium slope of surfaces.
DE: 5462 Polar regions
DE: 6225 Mars
SC: Planetary Sciences [P]
MN: Fall Meeting 2005