Juno Mission Redefines Jupiter’s Dimensions, Revealing a Smaller and More Oblate Gas Giant

NASA’s Juno mission has provided the global scientific community with the most accurate measurements of Jupiter’s physical dimensions to date, leading to a fundamental reassessment of the gas giant’s scale. A study featured in the journal Nature Astronomy in early February 2026 suggests that the planet is notably smaller and exhibits more significant polar flattening than has been assumed for nearly half a century. These newly defined geometric characteristics are vital for planetary science, offering a more precise foundation for modeling the planet’s complex internal composition.

For nearly fifty years, planetary models were based on data collected in the 1970s by the Pioneer 10, Voyager 1, and Voyager 2 spacecraft. These pioneering missions, however, could not fully account for the impact of Jupiter’s intense zonal winds, which created inconsistencies in the calculated dimensions. The Juno orbiter, which has been studying the Jovian system since 2016, achieved a breakthrough following a strategic mission reconfiguration in 2021. Its unique, highly elliptical orbit allowed researchers to analyze radio signal distortions as they traversed the atmosphere—a technique comparable to a medical computer tomography scan—providing a high-resolution view of the planet’s shape.

The research, spearheaded by an international team from the Weizmann Institute, indicates that Jupiter’s equatorial diameter at the 1-bar pressure level is approximately 8 kilometers smaller than previous estimates. The discrepancy is even more pronounced at the poles, where the radius was found to be 12 to 24 kilometers shorter, revealing a more compressed profile. Professor Yohai Kaspi of the Weizmann Institute noted that by incorporating 26 new data points, the team was able to reduce the margin of error regarding the planet’s shape by an entire order of magnitude.

The updated figures, released on February 2, 2026, define Jupiter’s equatorial radius as 71,488 kilometers and its polar radius as 66,842 kilometers at the 1-bar level. By factoring in the influence of zonal winds, which generate centrifugal variations of about 10 kilometers, scientists have successfully aligned gravitational measurements with atmospheric data. As the most massive entity in the solar system, Jupiter’s gravitational influence is a cornerstone of celestial mechanics. These refined parameters now serve as an essential benchmark for the study of Hot Jupiter exoplanets and ensure that internal structural models are consistent with the latest observational evidence.