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R. M. Haberle (NASA/Ames Research Center)
The low thermal inertia regions of Mars represent accumulations of fine dust particles, while the high thermal inertia regions contain much coarser particles. These thermal "continents" are thought to be due to aeolian processes with winds scouring out the finer particles in high thermal inertia regions and preferentially depositing them in the low thermal inertia regions. Furthermore, these regions are thought to be geologically young (~100,000 years) as they come and go with variations in Mars' orbit parameters. However, General Circulation Model simulations of the surface stress patterns on Mars show that the low thermal inertia regions of Tharsis, Arabia, and Elysium, are remarkably stable with respect to wind erosion for all plausible values of the planet's obliquity and season of perihelion. This suggests that the low thermal inertia regions are much older than previously thought, and that their origin may have begun very early in the planet's history when the topography stabilized into its present configuration.