Carbon Monoxide Affecting Planetary Atmospheric Chemistry

CO is an important component in many N-2/CH4 atmospheres, including Titan, Triton, and Pluto, and has also been detected in the atmosphere of a number of exoplanets. Numerous experimental simulations have been carried out in the laboratory to understand the chemistry in N-2/CH4 atmospheres, but very few simulations have included CO in the initial gas mixtures. The effect of CO on the chemistry occurring in these atmospheres is still poorly understood. We have investigated the effect of CO on both gas and solid phase chemistry in a series of planetary atmosphere simulation experiments using gas mixtures of CO, CH4, and N-2 with a range of CO mixing ratios from 0.05% to 5% at low temperature (similar to 100 K). We find that CO affects the gas phase chemistry, the density, and the composition of the solids. Specifically, with the increase of CO in the initial gases, there is less H-2 but more H2O, HCN, C2H5N/HCNO, and CO2 produced in the gas phase, while the density, oxygen content, and degree of unsaturation of the solids increase. The results indicate that CO has an important impact on the chemistry occurring in our experiments and accordingly in planetary atmospheres.