 In the early seventies, the possible existence of CO2 hydrates on Mars was proposed (Miller & Smythe 1970).Recent consideration of the temperature and pressure of the regolith and of the thermally insulating properties of dry ice and CO2 clathrate (Ross and Kargel, 1998) suggested that dry ice, CO2 clathrate, liquid CO2, and carbonated groundwater are common phases, even at Martian temperatures (Lambert and Chamberlain 1978, Hoffman 2000, Kargel "et al.