The size and shape of Jupiter

Jupiter, the fastest-rotating planet in the Solar System, exhibits a pronounced equatorial bulge, with its equatorial radius exceeding the polar radius by approximately 7%. This oblate shape reflects the combined effects of rapid rotation, complex internal structure, and atmospheric winds. Existing estimates of Jupiter’s shape, with uncertainties of about 4 km, are based on a single analysis of Voyager and Pioneer radio occultations from nearly five decades ago and do not account for the influence of Jupiter’s strong winds. The Juno spacecraft has recently returned numerous high-precision radio-occultation measurements, enabling a more accurate determination. Incorporating the effects of zonal winds, we derive Jupiter’s shape with an order-of-magnitude reduction in uncertainty. At the 1-bar pressure level, we find a polar radius of 66,842±0.4 km, an equatorial radius of 71,488 ±0.4 km, and a mean radius of 69,886 ± 0.4 km, which are 12 km, 4 km, and 8 km smaller than previous estimates, respectively. The results indicate that winds above the visible cloud tops are largely barotropic, showing minimal vertical variation. The updated shape has important implications for interior structure models, supporting a metal-enriched and cooler atmosphere, thereby helping reconcile discrepancies between models, Galileo probe measurements, and Voyager-derived temperatures. The refined radius profile also improves spatial referencing for pressure-dependent measurements, offering a more precise context for interpreting Jupiter’s atmospheric dynamics.