Steady-state flow of solid CO2: Preliminary results

To help answer the question of how much solid CO2 exists in the Martian sou th polar cap, we performed a series of laboratory: triaxial deformation exp eriments at constant displacement rate in compression on jacketed cylinders of pure, polycrystalline CO2. Test conditions were temperatures 150 < T< 1 90 K, hydrostatic confining pressures 5 less than or equal to P less than o r equal to 40 MPa, and strain rates 4.5 x 10(-8) less than or equal to (eps ilon) over dot less than or equal to 4.3 x 10(-4) s(-1). Most of the measur ements 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 re sults suggest that the:south polar cap on Mars is unlikely to be predominat ely solid CO2, because the elevation and estimated age of the cap is diffic ult to reconcile with the very weak rheology of the material.