The shape of Jupiter in light of the Juno radio occultation measurements

The shape of Jupiter is determined primarily by the planet’s rotation rate. Additionally, its interior density distribution plays an important role in defining its detailed shape. These characteristics can be used to calculate the gravitational potential. Then, the shape can be estimated using some estimate of either the polar or the equatorial radius of a specific pressure level, such as the 1 bar or 100 mb level. The shape is also affected by the zonal winds, creating a primarily positive anomaly in the order of 10 km at low latitudes. However, uncertainties in the observed cloud-level wind and the polar radius translate to an uncertainty in the shape with the same order of magnitude. Moreover, until now, only a few radio occultations, to which a shape estimate can be compared, have been performed, three by the Voyager spacecraft and three by the Pioneer spacecraft.

During the past year, the Juno mission performed a series of radio occultation measurements, enabling a more exact calculation of Jupiter's shape. Using these measurements, we calculate a new shape for Jupiter at the 100 mb pressure level. We then examine our results with respect to earlier shape estimations, mainly to the work of Lindal et al. (1981), and find a new, entirely consistent solution for the shape at the 1 bar level, the most commonly used level for the shape of Jupiter. These results bear importance for a wide range of research studies, from the interior modeling of Jupiter and other giant planets to the study of exoplanets.