Recent advances in the Io Plasma Torus Calibrations for Galileo, Juno, and Europa Clipper Radio Science Measurements

Abstract:

As of July 2020, NASA’s Juno spacecraft has performed 28 closest approaches of Jupiter, which provide opportunities to observe plasma electrons in the Io plasma torus along the radio ray path. Juno’s X-band and Ka-band radio links propagating through the Io plasma torus can be used to retrieve the integrated electron content. During each closest approach, Juno passed through the inner region between Jupiter and the Io plasma torus with Perijove altitudes of ~1.06 Jovian Radii, and the radio ray path crossed through the Io plasma torus once. Prior to the perijove 27 and 28 during Juno’s ascending equator crossing, a unique observation opportunity occurred where the electron content was measured simultaneously through both sides of the torus. The measured maximum integrated electron contents are ~30 TECU for the perijoves and ~120 TECU during the ascending equator crossings. Comparisons between observations and the corresponding IPT models derived from Voyager PLS data are presented. The results improve our understanding of the Io plasma torus effect on radio science measurements and help to generate calibrations to reduce the corresponding (non-gravity field-induced) radio frequency shift. Of particular importance to these calibrations are the Galileo radio science measurements and upcoming Europa Clipper radio science measurements, which are single-band radio measurements only, requiring a model for calibration of the Io plasma torus effect.