A Laboratory Study Relevant to the Isotopic Fractionation of Ammonia on Jupiter

AST0206270Kalogerakis同位素比值在行星大气起源和演化研究中起着重要作用。最近对木星大气层的观测表明，在大约400毫巴的气压下，15NH3有显著的亏损。氨和硫化铵云团的凝聚被认为是观测到的同位素耗竭的一个可能来源。目前，还没有关于固体NH3/NH4SH/H2O混合物的蒸汽压及其温度和同位素组成关系的实验结果。冷凝过程中相关的同位素分馏系数尚不清楚，也不能用目前的实验室信息对观察到的15NH3消耗做出解释。SRI国际的Konstantinos Kalogerakis博士将进行实验室实验，研究固体NH3/NH4SH/H2O混合物的固气平衡，并确定相关的同位素分馏系数。将测量与木星对流层相关的温度范围内的差蒸气压。这些结果将阐明所观察到的15NH3耗尽是一种局部现象，还是可能代表了木星的全球大气。木星的氮同位素比率被认为反映了太阳系前星云的氮同位素比率，这一事实使得拟议的研究结果不仅对模拟木星大气的形成和演化具有重要意义，而且可能对太阳系的演化也具有重要意义。***

AST 0206270KalogerakisIsotopic ratios play an important role in the study of the origins and evolution of planetary atmospheres. Recent observations of the atmosphere of Jupiter indicate a significant depletion of 15NH3 at a pressure of approximately 400 mbar. Condensation of the ammonia and ammonium hydrosulfide clouds has been suggested as a possible origin for the observed isotopic depletion. Currently, no experimental results are available on the vapor pressure of solid NH3 / NH4SH / H2O mixtures and its temperature and isotopic composition dependence. The relevant isotopic fractionation coefficients during condensation are not known, and an interpretation of the observed 15NH3 depletion cannot be made with the current laboratory information. Dr. Konstantinos Kalogerakis at SRI International will conduct laboratory experiments to investigate the solid-gas equilibrium of solid NH3 / NH4SH / H2O mixtures and determine the relevant isotopic fractionation coefficients. The differential vapor pressures will be measured for a range of temperatures relevant to the Jovian troposphere. These results will elucidate whether the observed 15NH3 depletion is a local phenomenon or whether it could represent the global atmosphere of Jupiter. The fact that the Jovian nitrogen isotopic ratio is believed to reflect that of the presolar nebula makes the results of the proposed study significant for modeling not only the formation and evolution of the Jovian atmosphere, but potentially the evolution of the Solar System as well. ***