Steady-state flow of solid CO2:: Preliminary results

To help answer the question of how much solid CO2 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 CO2. Test conditions were temperatures 150 < T< 190 K, hydrostatic confining pressures 5 less than or equal to P less than or equal to 40 MPa, and strain rates 4.5 x 10(-8) less than or equal to (epsilon) over dot less than or equal to 4.3 x 10(-4) s(-1). Most of the measurements follow a constitutive law of the form epsilon =A sigma(n)exp(-Q/RT), where sigma 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 CO2 is markedly weaker than water ice. Our results suggest that the:south polar cap on Mars is unlikely to be predominately solid CO2, because the elevation and estimated age of the cap is difficult to reconcile with the very weak rheology of the material.