Jupiter’s Size Revised: Juno Mission Reveals New Measurements & Updates Textbooks

For over half a century, our understanding of Jupiter’s size and shape has been based on data collected by NASA’s Pioneer and Voyager missions in the 1970s. Now, thanks to the ongoing Juno mission, that understanding is undergoing a significant revision. New data reveals that Jupiter is not only slightly smaller than previously estimated – by about 5 miles (8 kilometers) at the equator – but also more flattened at the poles, by approximately 15 miles (24 kilometers). This recalibration of Jupiter’s dimensions, published in February 2, 2026, in Nature Astronomy, has implications that extend far beyond our solar system.

The Juno spacecraft, orbiting Jupiter since 2016, has been instrumental in this updated assessment. Unlike previous measurements, Juno employed a technique called radio occultation, analyzing how radio signals bend and delay as they pass through Jupiter’s atmosphere. This allows scientists to probe the planet’s internal structure, even through its dense cloud cover. By measuring the changes in frequency caused by this bending, researchers can calculate temperature, pressure, and electron density at different depths within the atmosphere. The analysis incorporated data from 13 flybys and, crucially, accounted for the effects of Jupiter’s powerful zonal winds – the high-speed winds that encircle the planet in bands.

“We have analyzed how the radio signals are refracted when they pass through Jupiter’s atmosphere,” explained Maria Smirnova of the Weizmann Institute, a co-author of the study. This detailed analysis has reduced the uncertainty in Jupiter’s shape by an order of magnitude, from over 4 kilometers to just 0.4 kilometers.

The implications of this seemingly small adjustment are substantial. Jupiter’s radius serves as a critical calibration standard for modeling giant exoplanets – planets orbiting stars other than our sun. Astronomers rely on accurate measurements of Jupiter to interpret data from exoplanets detected using the transit method, where planets are identified by the slight dimming of their host star as they pass in front of it. A more precise understanding of Jupiter’s shape will allow for more accurate interpretations of data from these distant worlds.

“These few kilometers are significant – textbooks will need to be updated,” stated Yohai Kaspi, also of the Weizmann Institute and senior author of the study. The previous reference values, known as L81, overestimated Jupiter’s size. The updated average radius is 69,886 kilometers, 25 kilometers less than the previously accepted value.

Beyond refining our understanding of Jupiter’s external dimensions, the new data also sheds light on the planet’s interior. Previous models of Jupiter’s internal structure relied on the L81 reference radius. However, these models have consistently shown discrepancies with observational data, particularly regarding the abundance of heavier elements in Jupiter’s atmosphere.

By incorporating the new, smaller equatorial radius into these models, researchers find a better fit with gravitational and atmospheric measurements. This suggests that Jupiter may possess a more metal-rich and cooler atmosphere than previously thought. The revised data also impacts assumptions about Jupiter’s core, potentially refining our understanding of its composition, and formation.

The Juno mission’s continued analysis of data collected even after the primary mission concluded in 2025 demonstrates the enduring value of long-term planetary exploration. The radio occultation technique, refined and applied by Juno, has proven to be a powerful tool for unraveling the mysteries of gas giants. The recalibration of Jupiter’s size and shape is not merely a correction of past measurements; it’s a foundational step towards a more accurate and comprehensive understanding of not only Jupiter itself, but also the broader population of giant planets throughout the universe.