NASA's Juno Mission Refines Jupiter's Dimensions
Recent data from NASA's Juno spacecraft indicate that Jupiter is slightly smaller and flatter than previously estimated, prompting updates to planetary models.
Recent measurements from NASA's Juno spacecraft have refined our understanding of Jupiter's size and shape. The data reveal that Jupiter's equatorial diameter is approximately 8 kilometers narrower, and its polar diameter about 24 kilometers flatter than earlier estimates. These findings, published in Nature Astronomy in February 2026, suggest that Jupiter's mean radius is now calculated to be 69,886 kilometers, a reduction of 8 kilometers from previous measurements.
The study, led by researchers at the Weizmann Institute of Science, utilized radio occultation data from 13 Juno flybys. This technique involves analyzing how radio signals from the spacecraft bend as they pass through Jupiter's atmosphere, providing insights into the planet's internal structure. By incorporating the effects of Jupiter's zonal winds—east-west winds that penetrate approximately 3,000 kilometers beneath the 1-bar atmospheric pressure level—the team achieved a more precise determination of the planet's dimensions.
"This work provides the most precise measurement of Jupiter’s size and shape to date, reducing the uncertainty to ~0.4 km using Juno radio-occultation data," said Yohai Kaspi, lead researcher at the Weizmann Institute of Science. "The improved determination of Jupiter’s radius is important because the planet’s shape is a key parameter used in models of its internal structure and atmospheric dynamics."
These refined measurements are significant for enhancing models of Jupiter's interior and atmospheric dynamics. A smaller equatorial radius implies that the planet may have colder and metal-rich outer envelopes. Additionally, Jupiter serves as a calibration standard for gas giants within and beyond our solar system, making accurate measurements crucial for comparative planetary studies.
Looking ahead, future missions like the European Space Agency's Jupiter Icy Moons Explorer (JUICE), scheduled for radio occultation measurements between 2031 and 2034, may provide even deeper insights into Jupiter's atmosphere. However, with the current accuracy of 0.4 kilometers, significant changes to the planet's shape are not anticipated.
These findings underscore the dynamic nature of planetary science and the importance of continuous exploration to refine our understanding of the solar system's largest planet.