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

同位素比在研究行星大气的起源和演化中起着重要的作用。最近对木星大气的观测表明，15NH3在大约400毫巴的压力下显著耗竭。氨和氢硫化铵云的凝结被认为是观测到的同位素耗竭的可能来源。目前还没有关于固体NH3 / NH4SH / H2O混合物蒸汽压及其与温度和同位素组成关系的实验结果。在凝结过程中相关的同位素分馏系数是未知的，并且观测到的15NH3耗竭不能用目前的实验室信息来解释。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。将在与木星对流层有关的温度范围内测量蒸气压差。这些结果将阐明观测到的15NH3耗竭是一种局部现象，还是代表木星的全球大气。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，这一事实使得所提出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，而且对太阳系的演化也有潜在的意义。＊＊＊

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. ***