Formation Pathways, Stability, Hydration State and Spectral Characteristics of Amorphous Salts on Mars

THE OBJECTIVES OF THE PROPOSED WORK ARE TO 1) EXPLORE THE LIKELY FORMATION PATHWAYS FOR AMORPHOUS NANOCRYSTALLINE AND/OR POORLY CRYSTALLINE SULFATE CHLORIDE OXYCHLORINE AND MULTICOMPONENT SALTS 2) CHARACTERIZE THE HYDRATION STATE XRD AND SPECTRAL PROPERTIES OF AMORPHOUS SALTS EXPECTED FOR MARS AND 3) DESCRIBE THE THERMODYNAMIC PROPERTIES OF THESE SALTS AND THE SOLUTIONS AND/OR CRYSTALLINE MATERIALS FROM WHICH THEY FORM OVER A WIDE RANGE OF CONDITIONS. RECENT DISCOVERIES OF HYDRATED AMORPHOUS MATERIALS FROM THE MARS SCIENCE LABORATORY MISSION AS WELL AS DETECTIONS OF HYDRATED AMORPHOUS PHASES FROM ORBIT AND FROM OTHER LANDING SITES HAVE HIGHLIGHTED A NEED TO BETTER UNDERSTAND THE POSSIBLE PHASES THAT COULD COMPRISE THESE MATERIALS. FUNDAMENTAL QUESTIONS REMAIN ABOUT THE AMORPHOUS CONSTITUENTS IN MARTIAN SOILS AND IN PARTICULAR THE EXISTENCE AND PROPERTIES OF AMORPHOUS SALTS. THERE ARE A NUMBER OF MARS-RELEVANT PROCESSES THAT COULD LEAD TO AMORPHOUS OR NANOPHASE SALTS AND PREVIOUS STUDIES HAVE SUGGESTED THAT THEY COULD BE IMPORTANT CONSTITUENTS OF MARTIAN SURFACE MATERIALS. YET LITTLE IS KNOWN ABOUT THE FORMATION MECHANISMS STABILITY OR SPECTRAL PROPERTIES OF THESE PHASES. THERE ARE SEVERAL OUTSTANDING QUESTIONS RELATED TO AMORPHOUS SALTS LINKED UNDER THREE MAJOR OBJECTIVES. THE FIRST SET OF QUESTIONS RELATES TO FORMATION PATHWAYS FOR AMORPHOUS SALTS AS A FUNCTION OF COMPOSITION TEMPERATURE AND HUMIDITY CONDITIONS. THOUGH SOME SALTS HAVE BEEN INVESTIGATED ALREADY UNDER VARIOUS PATHWAYS OTHERS REMAIN UNEXPLORED. IMPORTANT TO UNDERSTANDING AMORPHOUS SALT FORMATION PATHWAYS IS DETERMINING THE DELIQUESCENCE RELATIVE HUMIDITY (DRH) OF CRYSTALLINE STARTING MATERIALS AT MARS-RELEVANT TEMPERATURES; HENCE THE INCLUSION OF DRH MEASUREMENTS IN THIS OBJECTIVE. THE SECOND SET OF QUESTIONS RELATES TO THE VISIBLE SPECTRAL X-RAY AND HYDRATION STATE CHARACTERISTICS OF THESE SALTS WHICH ARE IMPORTANT FOR THEIR DETECTABILITY USING PAST CURRENT AND FUTURE INSTRUMENTATION AT MARS. THE THIRD SET OF QUESTIONS RELATES TO THE STABILITY OF AMORPHOUS SALTS. THE RH-TEMPERATURE CONDITIONS UNDER WHICH AMORPHOUS SALTS FORM AND ARE STABLE AS WELL AS THE RATES OF TRANSFORMATIONS ARE NOT WELL CONSTRAINED PARTICULARLY FOR TEMPERATURES