Radio observations of the planets: The importance of laboratory measurements

Abstract

In this paper we summarize the needs of planetary radio astronomers regarding future laboratory measurements. We present a short review of our present knowledge regarding planetary atmospheres and surfaces, and show our progression in data analysis over time when more and better laboratory data became available. To further constrain elemental abundances and understand the dynamics and cloud physics in the giant planet's atmospheres, we need laboratory data on the line broadening parameters of H2S gas under Uranian/Neptunian conditions, on the far wings of the H2S and NH3 line profiles, and on the dielectric properties of CH4−, NH3−, H2S−, and NH4SH‐ice. To obtain a better understanding of Venus' atmosphere, we need measurements of the absorption coefficient of gaseous H2SO4 at millimeter wavelengths. Accurate measurements of the center frequencies of the CO lines are necessary to determine wind velocity fields in Venus' and Mars' atmospheres. The modeling of radiative transfer through particulate material is the most difficult aspect of the analysis of microwave observations of planetary surfaces. Laboratory experiments that separately measure the absorption and scattering properties of lunar soils and/or terrestrial rock powders at frequencies from ∼1 to 200 GHz would provide a valuable addition to existing data at 450 MHz, 35 GHz, and far infrared frequencies. These data would be applied to the analysis of microwave spectra of planetary surfaces to help separate the effects of radiative transfer from those of nonlinear heat conduction and internal heat sources.