Photocatalytic Production of Organic Compounds from CO and H ₂ O in a Simulated Martian Atmosphere

Abstract

Current ideas regarding the abiogenic synthesis of organic compounds on the planets rest on the theories of Oparin (1) and Urey (2), and on the experiments of Miller (3) and others, showing that the synthesis of biologically important compounds on the primitive earth was favored by the chemically reducing character of the primitive atmosphere. The importance of an excess of a reduced gas such as hydrogen, methane, or ammonia in laboratory simulations of these processes has often been pointed out (4). In view of these findings, it appears a priori unlikely that a synthesis of organic matter would be demonstrable in a gas mixture compositionally similar to the oxidized atmosphere of Mars. This atmosphere consists almost entirely of CO2 (5) with 0.1-0.3% CO (5, 6) and a small, seasonally variable quantity of water (7). Small amounts of other gases are not excluded. The mean surface pressure is about 6.5 mb (8). Solar ultraviolet (UV) reaching the surface is filtered through the CO2, which effectively absorbs wavelengths shorter than 1950 A. Thus, little energy is available at the surface for the activation of C02, CO, or water.We have performed organic synthesis experiments with mixtures of C02, CO, and H20 exposed to UV in the presence of soil or powdered vycor glass. The purpose of these tests was to uncover possible sources of error in an experiment, planned for the first Mars lander, designed to detect biosynthesis of organic matter in Martian soil (9). The The reservoirs were then brought to a total pressure of 1 atm by filling with diluent gas and with about 50 ml of liquid water previously flushed with the diluent gas. The [14C]CO reservoirs were attached to a pyrex manifold which had five positions for attachment of sample chambers. The latter consisted of quartz tubes (1.3 X 8 cm) with a detachable pyrex section containing a stopcock. Each chamber had a gas volume of about 5.5 ml. The chambers were evacuated and flushed with diluent gas, then filled manometrically to 1 atm with ['4C]CO and diluent gases. The pressure in the reservoir was maintained at 1 atm by adding water flushed with diluent gas.The vacuum system contained a liquid nitrogen trap to prevent diffusion of impurities from the mechanical vacuum pump. The vacuum indicator was a Wallace and Tiernan Gage. The gas reservoirs, manifold, and sample chambers were constructed of new glass that presumably had never been exposed to mercury. Also, all glassware was cleaned with 8 N HNO3 to minimize adventitious mercury contamination.The organic soil was an arable, fertile, brown soil with particle size less than 1 mm. Before exposure to [14C]CO, the soil was sterilized overnight in an oven at 1750C and then equilibrated for 1 hr at 100% relative humidity at 23°C.The vycor substratum was 80-100 mesh, highly fractured particles with a surface area of 173 m2/g. Before use, the vycor was heated to 7200C in air and equilibrated with water vapor as described above.Sample chambers containing gas mixtures were irradiated in a horizontal position with the soil...

Viking on Mars: The carbon assimilation experiments

“…Although solar wavelengths as short as 200 nm reach the surface c:if Mars we have excluded wavelengths shorter than 320 nm from the 'test chamber in order to prevent a nonbiological, photocatalyzed synthesis of organic compounds from CO and adsorbed water vapor that we find to occur on. silicate and other mineral surfaces irradiated with ultraviolet shorter than 300 nm [Hubbard et al, 1971[Hubbard et al, , 1973[Hubbard et al, , 1975. Since these short wavelengths are generally destructive to organic matter except under the special conditions of the synthesis, we assume that Martian life, if it exists, must also avoid this spectral region; its deletion from the radiation entering the test chamber therefore does not constitute a significant change in the biological environment.…”

The missing organic molecules on Mars

“…The examination suggests that organic compounds that arrive on Mars via meteorite are most likely to be converted to carboxylic acid derivatives that would not be easily detected by GC-MS. Organic molecules generated on Mars itself by nonbiological (11)(12)(13)(14) or (entirely hypothetical) biological synthesis (15) should suffer similar fates at or near the surface.…”

Oligoglyceric acid synthesis by autocondensation of glyceroyl thioester

“…It seems very likely that formaldehyde was available on the primitive earth, since it can be produced under a variety of prebiotic conditions (Garrison e_t_al. 1951» Miller 19571 Getoff et al 1960Hubbard et al 1971;Bar-Nun and Hartman 1978;Miller and Schlesinger 1984), and model studies of the early Earth show its photochemical synthesis in the primitive atmosphere and its rain-out to the Earth's surface (Pinto et.al. 1980;Canute et al 1983;Kasting and Pollack 1984).…”

“…Formaldehyde has been synthesized under a variety of prebiotic conditions (Garrison et al 1951;Miller 1957;Getoff et al I960;Hubbard et al 1971;Bar-Nun and Hartman 1978;Miller and Schlesinger 1984), and models of the Earth's primitive atmosphere show photochemical synthesis of formaldehyde in the early atmosphere and its transport to the Earth's surface by rain-out (Pinto et al 1980;Canute et al 1983;Kasting and Pollack 1984 Glyceric acid hydroxamate was prepared by the method of Thompson (1951).…”