Spectral broadening measurements of the ionospheres of Jupiter and Saturn

Abstract

When Pioneers 10 and 11 flew by Jupiter, their 2.3-GHz monochromatic radio signals underwent substantial spectral broadening as they propagated through the planet's ionosphere^1,2. Although spectral broadening has been observed during radio occultation by the solar corona^3,4, the Pioneer measurements of Jupiter represent the first time it has been observed during radio occultation by a planetary atmosphere. The Pioneer data are also unique in that r.f. spectral broadening, a scattering phenomenon normally associated with strong intensity scintillations (σ²_χ ∼ 1 where σ²_χ is the variance of the log-amplitude scintillations), occurred when the intensity scintillations were weak. This unusual opportunity makes it possible to compare the theory for spectral broadening with the more widely used weak intensity scintillation theory^5,6. We report here that good agreement is found, and present the inferred characteristics of the electron density irregularities for the ionospheres of both Jupiter and Saturn. The Saturn results are based on measurements made during the 1979 Pioneer 11 encounter of Saturn.