Perchlorate induced low temperature carbonate decomposition in the Mars Phoenix Thermal and Evolved Gas Analyzer (TEGA)

Simulated Thermal Evolved Gas Analyzer (TEGA) analyses have shown that a CO₂ release detected between 400°C and 680°C by the Phoenix Lander's TEGA instrument may have been caused by a reaction between calcium carbonate and hydrated magnesium perchlorate. In our experiments a CO ₂ release beginning at 385 ± 12°C was attributed to calcite reacting with water vapor and HCl gas from the dehydration and thermal decomposition of Mg-perchlorate. The release of CO₂ is consistent with the TEGA detection of CO₂ released between 400 and 680°C, with the amount of CO₂ increasing linearly with added perchlorate. X-ray diffraction (XRD) experiments confirmed CaCl₂ formation from the reaction between calcite and HCl. These results have important implications for the Mars Science Laboratory (MSL) Curiosity rover. Heating soils may cause inorganic release of CO₂; therefore, detection of organic fragments, not CO₂ alone, should be used as definitive evidence for organics in Martian soils.