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Reconstructing Callisto’s Gravity Field through the Combination of JUICE 3GM and Europa Clipper Radio Science Experiments

Presentation #314.01 in the session Icy Satellites, Fields and Particles (Poster + Lightning Talk)

Published onOct 23, 2023
Reconstructing Callisto’s Gravity Field through the Combination of JUICE 3GM and Europa Clipper Radio Science Experiments

This work presents a synergistic approach for assessing and reconstructing Callisto’s gravity field by combining data from the ESA JUpiter ICy moons Explorer (JUICE) 3GM (Gravity and Geophysics of Jupiter’s Moons) experiment and the NASA Europa Clipper radio science experiment. JUICE and Europa Clipper will visit the jovian system in an overlapping time span ranging from 2030 to 2035. By leveraging the complementary capabilities of these two missions, we investigate one of the possible sinergies between the radio science experiments. The JUICE 3GM radio science experiment will utilize a 5-way multifrequency link (X/X, X/Ka, and Ka/Ka band) to obtain highly accurate Doppler and ranging data. These measurements are expected to have an accuracy level of approximately ~0.017 mm/s @60s and 6 cm @300 s, almost at all solar elongation angles. Europa Clipper will rely only X/X and X/Ka Doppler measurements with a predicted accuracy of ~0.088 mm/s at 60 s of integration time. A key goal of the 3GM experiment is to estimate the gravity field and tidal response of Callisto, by measuring the tidal Love number k2. The accuracy of this estimation heavily relies on sampling the Callisto gravity field at different mean anomalies along its orbit around Jupiter. Thus, an ideal flyby distribution would include encounters at the apojove and perijove, where the tidal effect is strongest. JUICE will conduct a total of 21 Callisto flybys, 16 of them are located at a mean anomaly close to -90°. Additionally, only one of them will sample the gravity field at the apojove and one at the perijove. Europa Clipper will encounter Callisto 9 times, with 4 of those occurring near an apojove. Despite JUICE’s radio tracking measurements being more accurate than those of Europa Clipper, the different of the encounter geometries offer potential benefits for the overall reconstruction of Callisto’s gravity field and tidal response. By means of numerical simulation, we show the difference between a single mission scenario and a combined mission results, in terms of potential improvement of the scientific outcome. Additionally, we present a risk mitigation strategy to address potential data loss during flybys, e.g., due to adverse weather conditions at the station or the spacecraft entering safe mode. The integration of JUICE 3GM and Europa Clipper radio science experiments could enable a comprehensive analysis of Callisto’s gravity field, shedding light on its interior structure, geophysical processes, and potential subsurface water reservoirs.

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