As part of HEDS, we propose to explore the practicality of recovering minerals from the Martian soils using supercritical carbon dioxide as a solvent. On earth, water is the solvent of choice and it is used to dissolve and recover a wide range of minerals. On Mars, however, there is very little water. Carbon dioxide becomes a supercritical fluid when it is heated to 31.1 degrees Celsius and compressed to a pressure of 1,073 pounds per square inch.
Supercritical fluids have properties that resemble both gas and liquid.
These include the ability to dissolve other materials. This solubility is strongly related to the pressure of the fluid. By alternating the pressure correctly we can cause materials to dissolve in the supercritical fluid and then to crystallize out. Most of the current research on supercritical fluids has focused on the solubility of organic compounds. For example, decaffeinated coffee is made by extracting caffeine from coffee beans with supercritical carbon dioxide.