Steady-state flow of solid CO2: Preliminary results

Abstract

To help answer the question of how much solid CO 2 exists in the Martian south polar cap, we performed a series of laboratory triaxial deformation experiments at constant displacement rate in compression on jacketed cylinders of pure, polycrystalline CO 2 . Test conditions were temperatures 150 < T < 190 K, hydrostatic confining pressures 5≤ P ≤40 MPa, and strain rates 4.5×10 −8 ≤ ε ≤4.3×10 −4 s −1 . Most of the measurements follow a constitutive law of the form ε = Aσ n exp(−Q/RT), where σ is the applied differential stress, R is the gas constant, and the other constants have values as follows: A = 10 3 86 MPa −n s −1 , n = 5.6, and Q = 33 kJ/mol. Solid CO 2 is markedly weaker than water ice. Our results suggest that the south polar cap on Mars is unlikely to be predominately solid CO 2 , because the elevation and estimated age of the cap is difficult to reconcile with the very weak rheology of the material.