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A Programme of Research in Planetary and Solar System Science - Understanding the Formation of Phosphorus and Nitrogen Compounds

Middle/Upper Atmosphere – Current Projects

Project Reference: ST/P000517/1

Science and Technology Facilities CouncilPhosphorus (P) and Nitrogen (N) are important components of biologically interesting molecules. This consolidated proposal contains two projects; firstly looking at mechanisms of generating bioavailable phosphorus released from meteoric particles in the atmospheres of early Earth, Mars and Venus and secondly examining the incorporation of atomic nitrogen into complex organic molecules relevant for the production of astrobiologically interesting compounds and aerosol particles in Titan's atmosphere (one of Saturn's moons).

Phosphorus and the Inner Planets - The major route to the generation of atmospheric phosphorus is its release as meteoric particles burn up in the upper atmospheres of the inner planets. We seek to characterize this process and to determine the amount of P entering into the atmosphere. Once released elemental P will start to be oxidized by O, OH, O2 and O3. We have identified crucial steps in this oxidation process that can lead to phosphorus compounds, phosphates and phosphites, which have markedly different bioavailability on reaching the planet's surface. We will combine our meteor ablation studies and kinetic data within atmospheric models to determine the relative efficiency of phosphate and phosphite production and estimate the total flux of P to the planet surface. The project links to on-going studies of the Martian atmosphere such as the MAVEN project.

Nitrogen and Titan - Titan is an interesting solar body, like Earth its atmosphere is predominantly nitrogen, N2, but Titan is surrounded by an orange haze comprised of aerosol particles containing complex organic molecules. The exact composition and mechanism of formation of these particles is unknown. For the last 10 years or so, the Cassini mission has been sending back data on Titan (and Saturn) which has stimulated research in a variety of areas.

Nitrogen is generally extremely unreactive in Titan's lower atmosphere, however, in the upper reaches of Titan's atmosphere absorption of high energy radiation and other processes generate N atoms. We will characterize critical reactions in the incorporation of these atomic species into the hydrocarbons that exist in Titan's atmosphere. The HCN molecule lies at the heart of this chemistry, yet there is very poor agreement between measurements and models of this species. We will use our laboratory data (measurements of the rates of these reactions at the cold temperatures and low pressures of Titan's upper atmosphere) and atmospheric models to try and close the gap between measurements and models and to assess the mechanisms by which N is incorporated into Titan's haze layer.