The chlorine cycle on Jupiter and Saturn

Hydrogen halides provide key insights into giant planet atmospheres but their detection has so far remained elusive. Herschel/HIFI.s low noise and high spectral resolution provides a unique opportunity to detect these species for the first time with an estimated sensitivity at the sub part per trillion level an improvement of over three orders of magnitude on the best measurements currently available.Observing hydrogen halide species provides an exciting new avenue for studying chemical and dynamical processes at work on the giant planets. This proposal will focus on HCl the halide with the highest predicted abundance and detectablity. HCl could have an internal or external origin although models predict that an external origin from influx of extraplanetary material is the most likely.The observed HCl abundances will be used to: (1) Determine the magnitude of external Cl sources and compare exogenic flux environments and physiochemical processes between Jupiter and Saturn. (2) For Jupiter, by comparing the Cl flux to the O flux (from H2O), we can determine the excess Cl flux and measure the proportion of Io.s plasma torus that enters the top of the jovian atmosphere. This unique measurement would have implications for the whole Jupiter system. (3) Use the gradient of the vertical profile to determine the efficiency of HCl scavenging by NH3 in the stratosphere and constrain the stratospheric chlorine cycle. (4) Provide the most stringent test of interior thermochemical models to date, by determining limits on the abundance of HCl in the troposphere. This will help constrain the speed at which internal material is dredged up and the efficiency of HCl depletion by formation of ammonia salts. Comparing HCl abundances between Jupiter and Saturn will allow us to probe these processes under different internal and external environments, providing further insight. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]