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

Sri International, Menlo Park CA

Investigators

Abstract

AST 0206270 Kalogerakis Isotopic 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. ***