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

磷(P)和氮(N)是生物学上有趣的分子的重要组成部分。这一综合建议包括两个项目；首先，研究早期地球、火星和金星大气中的大气颗粒释放出的生物可利用磷的产生机制；其次，研究氮原子与复杂有机分子的结合，这些有机分子与在土卫六（土星的卫星之一）大气中产生天体生物学上有趣的化合物和气溶胶颗粒有关。磷和内行星——大气中磷的主要产生途径是在内行星的上层大气中，随着大气粒子的燃烧而释放出来。我们试图描述这一过程，并确定进入大气的P的量。元素P一旦释放，就会开始被O、OH、O2和O3氧化。我们已经确定了氧化过程中的关键步骤，这些步骤会产生磷化合物、磷酸盐和亚磷酸盐，它们在到达地球表面时具有明显不同的生物利用度。我们将结合我们的流星消融研究和大气模型中的动力学数据来确定磷酸盐和亚磷酸盐生产的相对效率，并估计P到行星表面的总通量。该项目与MAVEN项目等正在进行的火星大气研究相关联。氮和土卫六——土卫六是一个有趣的太阳天体，像地球一样，它的大气主要是氮和氮，但土卫六周围是由含有复杂有机分子的气溶胶颗粒组成的橙色薄雾。这些粒子的确切组成和形成机制尚不清楚。在过去10年左右的时间里，卡西尼号任务一直在发回土卫六（和土星）的数据，这刺激了各个领域的研究。氮在土卫六的低层大气中通常是极不活泼的，然而，在土卫六大气层的上层，吸收高能辐射等过程会产生N原子。我们将描述这些原子与土卫六大气中存在的碳氢化合物结合的关键反应。HCN分子是这种化学反应的核心，然而，该物种的测量结果和模型之间的一致性非常差。我们将使用我们的实验室数据（在土卫六上层大气的低温和低压下这些反应速率的测量值）和大气模型来尝试缩小测量值和模型之间的差距，并评估N被纳入土卫六雾霾层的机制。

Phosphorus (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.