Accurate knowledge of the centimeter- and millimeter-wavelength absorptivity of ammonia is necessary for the interpretation of the emission spectra of the jovian planets. The objective of this research has been to advance the understanding of the centimeter- and millimeter-wavelength opacity spectra of ammonia under jovian conditions using a combination of laboratory measurements and theoretical formulations. As part of this research, over 1000 laboratory measurements of the 2-4 mm-wavelength properties of ammonia under simulated upper and middle tropospheric conditions of the jovian planets, and approximately 1200 laboratory measurements of the 5-20 cm-wavelength properties of ammonia under simulated deep tropospheric conditions of the jovian planets have been performed. Using these and pre-existing measurements, a consistent mathematical formalism has been developed to reconcile the centimeter- and millimeter-wavelength opacity spectra of ammonia. This formalism can be used to estimate the opacity of ammonia in a hydrogen/helium atmosphere in the centimeter-wavelength range at pressures up to 100 bar and temperatures in the 200 to 500 K range and in the millimeter-wavelength range at pressures up to 3 bar and temperatures in the 200 to 300 K range. In addition, a preliminary investigation of the influence of water vapor on the centimeter-wavelength ammonia absorptivity spectra has been conducted. This work addresses the areas of high-sensitivity centimeter- and millimeter-wavelength laboratory measurements, and planetary science, and contributes to the body of knowledge that provides clues into the origin of our solar system. The laboratory measurements and the model developed as part of this doctoral research work can be used for interpreting the emission spectra of jovian atmospheres obtained from ground-based and spacecraft-based observations. The results of the high-pressure ammonia opacity measurements will also be used to support the interpretation of the microwave radiometer (MWR) measurements on board the NASA Juno spacecraft at Jupiter.

The object of this research program has been to provide a baseline for microwave remote sensing of ammonia and water vapor in the atmosphere of Jupiter through laboratory measurements of their microwave absorption properties. Jupiter is not only the largest planet in our solar system, but one of the most interesting and complex. Despite a handful of spacecraft missions and many astronomical measurements, much of Jupiter s atmospheric dynamics and composition remain a mystery. Although constraints have been formed on the amount of certain gases present, the global abundances and distributions of water vapor (H2O) and ammonia (NH3) are relatively unknown. Measurements of H2O and NH3 in the Jovian atmosphere to hundreds of bars of pressure are best accomplished via passive microwave emission measurements. For these measurements to be accurately interpreted, however, the hydrogen and helium pressure-broadened microwave opacities of H2O and NH3 must be well characterized, a task that is very difficult if based solely on theory and limited laboratory measurements. Therefore, accurate laboratory measurements have been taken under a broad range of conditions that mimic those of the Jovian atmosphere. These measurements, performed using a newly redesigned high-accuracy system, and the corresponding models of microwave opacity that have been developed from them comprise the majority of this work. The models allow more accurate retrievals of H2O and NH3 abundances from previous as well as future missions to Jupiter and the outer planets, such as the NASA New Frontiers class Juno mission scheduled for launch in 2011. This information will enable a greater understanding of the concentration and distribution of H2O and NH3 in the Jovian atmosphere, which will reveal much about how Jupiter and our solar system formed and how similar planets could form in other solar systems, even planets that may be hospitable to life.