MODELING OF JUPITER MILLIMETER-WAVE EMISSION UTILIZING LABORATORY MEASUREMENTS OF AMMONIA (NH3) OPACITY

Radiative transfer models which have been used to compute Jupiter's millimeter wave emission do not agree well with the existing radio astronomical observations (e.g., de Pater and Massie, 1985). This apparent discrepancy has gone largely unexplained due to a lack of laboratory absorption data at these wavelengths coupled with uncertainties in the calibration of millimeter wave observations. Gaseous ammonia (NH3) is the largest source of millimeter wave opacity on Jupiter. Previous laboratory measurements at 7.5- to 9.38-mm were inconclusive as to which theoretical line shape most accurately describes the millimeter absorptivity of NH3 (Joiner et al., 1989). We have made additional laboratory absorption measurements of gaseous ammonia at a shorter wavelength (3.2 mm) where the theoretical line shapes can be better evaluated. We have conducted measurements at a temperature of 210 K, at pressures ranging from 1 to 2 atm, and in a mixture consisting of 85.56% hydrogen (H-2), 9.37% helium (He), and 5.07% ammonia (NH3). We give a revised formalism for computing NH3 absorption in an H-2/He atmosphere using the Ben-Reuven line shape. We investigate several other potential millimeter wavelength absorbers and give revised formalisms for computing their absorption. We compiled a list of Jupiter's reliable millimeter wavelength observations. We compare our list of observations with synthetic emission spectra utilizing our revised expressions for computing absorption.