Analysis of Jupiter's atmosphere using Juno's radio occultations

Abstract

The shallow layers of the Jovian atmosphere, the only regions accessible to direct investigation through in situ sampling and remote sensing experiments, are the looking glass through which the unknowns of Jupiter's structure are revealed. Radio occultation experiments have proved to offer invaluable opportunities to investigate the atmospheric dynamics of Jupiter, akin to descending a probe into its upper layers, offering unique insights into the thermal structure and composition. Since July 2023, Juno's extended mission has presented a multitude of such opportunities, with each passing month bringing forth a new experiment, a first since the Voyager missions. In these experiments, as the Juno spacecraft orbits Jupiter, it is obscured by the planet along its trajectory. As the electromagnetic signal from the spacecraft travels towards Earth, it traverses through Jupiter's atmosphere, resulting in refraction on the signal. This refraction is recorded on the ground station as a frequency shift, known as the Doppler shift, compared to its expected frequency in a vacuum environment. Radio occultation experiments capitalize on these refraction effects to investigate and decipher the atmospheric vertical properties of the planetary atmosphere up to 0.5 bar. The Juno radio occultations of Jupiter operated in a coherent two-way mode, utilizing multi-frequency link signals. Consequently, this study necessitated the use of an optimization method employing ray tracing techniques to track both the uplink and downlink signal through the neutral atmosphere in X- and Ka-band, enabling the extraction of vertical profiles of atmospheric parameters. The analyzed atmospheric pressure-temperature profiles highlight the potential of Juno's radio occultation experiments in elucidating the relatively unknown neutral atmosphere of Jupiter. In this presentation we present initial results from Juno's first year of radio occultations, analyse the measurement sensitivity concerning density and temperature, investigate the vertical temperature profiles at different latitudes and discuss their implications regarding the dynamics of Jupiter.