Photo-induced free radicals on a simulated Martian surface

Abstract

THE atmospheric pressure at the surface of Mars is about 5.5 mbar and the atmosphere is composed mainly of CO2 with trace amounts of CO, O2 and H2O (refs 1 and 2). The Martian dust has an intermediate SiO2 content of 60 ± 10% (ref. 3). Although it has been thought that the synthesis in a planetary atmosphere of organic compounds relevant to the origin of life requires chemically reducing conditions, Hubbard and colleagues4,5 have reported the synthesis of organic compounds by ultraviolet irradiation (λ > 250 nm) of a solid with a gas mixture adsorbed which is compositionally similar to the oxidised atmosphere of Mars. Since the question whether organic compounds could have been formed on the surface of Mars is of fundamental importance to the concept of chemical evolution and to the interpretation of results from the future Mars Viking Mission molecular analysis experiment, we have attempted to confirm these results while concentrating on identifying the primary process and the reactive intermediates involved. Here we describe the electron spin resonance (ESR) study of free radicals in the ultraviolet irradiation of a simulated Martian surface. (A preliminary account was presented at the Fourth International Conference on the Origin of Life, Barcelona, Spain, June 1973.)