P082-0005
Updates on Jupiter’s gravity from the latest Juno data

Wednesday, 16 December 2020
Poster
Daniele Durante1, Virginia Notaro1, Paolo Racioppa2, Luciano Iess2, Marzia Parisi3, Dustin Buccino4, William M Folkner4, Marco Zannoni5, Luis Gomez Casajus6, Paolo Tortora5, David J Stevenson7 and Scott J Bolton8, (1)Sapienza University of Rome, Rome, Italy, (2)Sapienza University of Rome, Department of Mechanical and Aerospace Engineering, Rome, Italy, (3)Jet Propulsion Laboratory, Pasadena, CA, United States, (4)Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, United States, (5)University of Bologna, Department of Industrial Engineering, Bologna, Italy, (6)University of Bologna, Bologna, Italy, (7)California Institute of Technology, Pasadena, CA, United States, (8)Southwest Research Institute, San Antonio, TX, United States
Abstract:
As of December 2020, Juno is close to completing its nominal mission. From Doppler data acquired during 30 close perijove passes in the last 4 years, Juno provided new insights into Jupiter’s interior structure by determining its gravity field. These results were made possible by the onboard and ground radio science instrumentation, enabling radial velocity (Doppler) measurements with accuracy as low as 10 micron/s at an integration time of 60 s.

The gravity field of the planet is recovered though the precise reconstruction of Juno’s orbital motion, which relies on an accurate model of the spacecraft dynamics. Standard gravitational and non-gravitational accelerations are easily accounted for, but cannot fully explain (at a level of few tens of micron/s) Juno Doppler data.

Conventional models have been updated to account for the larger available dataset. Jupiter’s spin axis motion precesses approximately around the normal to the Sun-Jupiter invariable plane due to the gravitational torques exerted on the Jupiter system by Solar System’s bodies. In the approach used to process gravity Doppler data acquired till the end of 2018 (Durante, et al., 2020), Jupiter’s pole position was estimated assuming a linear precession model. While a linear approximation was satisfactory to process the data till mid-mission, the integration of Jupiter’s pole motion shows an increasingly non-linear behaviour as the mission progresses towards the nominal end in July 2021. Therefore, we integrated Euler's equations for Jupiter subject to the gravitational torques from the Galilean satellites and the Sun. A more precise precession model not only allowed a better estimate of the accelerations acting on Juno, but also enabled a direct estimation of Jupiter's polar moment of inertia, a quantity with fundamental implications for Jupiter’s interior structure.

In addition, since Jupiter is a gas giant, other unconventional phenomena (never observed in terrestrial planets’ gravity fields) may complicate the global picture. Different phenomena can be at play, including: 1) small-scale atmospheric vortices, 2) deep-rooted gravity anomalies, 3) normal modes (acoustic or gravity). We analyzed these different options and report on preliminary results we found, with the aim of putting constraints on some characteristics of these phenomena.

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