Mineralogical analysis of Martian soil and rock by a miniaturized backscattering Mossbauer spectrometer

The general scientific objectives of an in situ experiment employing a Mossbauer spectrometer on a Martian lander are, for both rock and soil samples, identification and relative abundance of iron-bearing minerals (including carbonates, phyllosilicates (clays), hydroxyoxides, phosphates, oxides, silicates, sulfides, sulfates), measurement of the ferric (Fe3+) to ferrous (Fe2+) ratio, determination of the properties of magnetic phases including the size distribution of magnetic particles (nanophase versus larger particles) in the Martian soil. These data provide information about the nature and extent of atmosphere-surface chemical and physical weathering processes involving Fe-bearing phases. These objectives are directly relevant to studying the evolution of volatiles and climate over time on Mars because surface materials are major volatile sinks. In fact one of the major problems associated with understanding the evolution of volatiles on Mars is understanding the processes in the past and/or present that are responsible for oxidizing the red planet. A miniaturized backscattering Mossbauer spectrometer, developed at the Technical University of Darmstadt, is reported on which is a flight prototype of an instrument that could be used for in situ analysis as part of a payload of a Martian lander. Its critical instrument parameters are < 300 g mass, 250 cm(3) volume, about 0.4 W power, and about 300 mCi (at launch) Co-57 radiation source. Results of test measurements on Mars sample analogues will be presented. As an example for laboratory weathering studies on Fe-bearing phases, which are important for analysis and interpretation of returned data from Mars, first results of the study of weathering of basalt under CO2 and CO2-O-2 atmospheres will be presented and discussed. Copyright (C) 1996 Elsevier Science Ltd