CHEMISTRY OF MARS AS REVEALED BY THE VIKING LABELED RELEASE EXPERIMENT

An intriguing scientific puzzle emerged from the 1976 Mars Viking microbiology investigations. In one of these three experiments, the Labeled Release (LR) experiment, unambiguous positive signals were obtained. A total of 9 cycles of this experiment on Mars established the kinetics, successive injection behavior, temperature response correlation, photochemical role and heat stability. Some aspect of the phenomenon were not biology-like. Other evidence argues against a biological interpretation.; In order to seek a more chemically reasonable model, as opposed to the models invoking exotic or highly reactive compounds proposed by other post-Viking investigators, intensive laboratory simulation guiding by thermodynamic and physical chemistry principles have been employed. Mass spectrometry and C-14 isotropic tracer techniques were used to follow the reaction. In addition, an inert atmosphere, high vacuum technique as well as procedures to ensure sterility were used to provide chemically pure and controlled conditions for the simulations.; It was found that the nutrient used on Mars contained a small amount of ethanol, a component which had been overlooked by most Viking-related scientists, and it was discovered that the ethanol played a major role in the LR phenomenon. The exact ethanol content in the LR nutrient was analyzed.; By using proper combinations of acidity and desiccation levels of Martian soil model, all the key features of the LR response have been reproduced. The mutually consistence of this chemical explanation with all the physical chemical information known about Mars' environment proved the high possibility of the model as to occur in the flight experiment.; During the course of the LR simulation studies, a novel morphological form of partially dehydrated metal sulfates was discovered. Upon periodic cycling of moisture in and out of the powder, as presumably occurs on Mars, a very open coral-like network structure of high surface area is formed. This new material seems to possess some interesting physical properties and catalytic activities.