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Leveraging high-precision radio occultation measurements from NASA’s Juno mission, planetary scientists have significantly refined the shape of Jupiter. Their findings reveal that the planet’s polar, equatorial, and mean radii are smaller than earlier estimates from NASA’s Pioneer and Voyager missions, with substantially reduced uncertainty.
This vibrant visible-light image of Jupiter was captured using the Hubble Wide-Field Camera 3 on January 11, 2017. Featured prominently are the Great Red Spot and a long brown feature known as the “Brown Barge,” stretching approximately 72,000 km (around 45,000 miles) from east to west, with Red Spot Junior (Oval BA) on the lower right. Image credits: NASA / ESA / NOIRLab / NSF / AURA / Wong et al. / De Peyter et al. / M. Zamani.
“Jupiter, recognized as the largest planet in our solar system, is an almost oblate spheroid due to its rapid rotation of 9 hours, 55 minutes, and 29 seconds, causing a slight flattening at the poles and a bulge at the equator,” stated Dr. Eli Galanti of the Weizmann Institute of Science.
“This unique shape results from the gravitational forces pulling inward and centrifugal forces pushing outward from its rotation axis. Consequently, Jupiter’s equatorial radius is approximately 7% larger than its polar radius.”
“For celestial bodies with a uniform density, the shape is ideally ellipsoidal. However, Jupiter’s internal density varies significantly from the cloud layer of about 1 bar, where density is less than 1 kg/m3, to deeper layers reaching densities of several thousand kg/m3.”
“This density variation causes the planet’s shape to deviate from a simple ellipsoid by tens of kilometers, as reflected in fluctuations of the gravitational field across latitudes.”
“Additional alterations in Jupiter’s shape are induced by strong zonal winds detected at cloud level,” Dr. Galanti continued.
“These winds modify the centrifugal force, leading to variations of about 10 km mainly at lower latitudes.”
Historically, Jupiter’s dimensions were based on data from six radio occultation experiments conducted by NASA’s Pioneer and Voyager missions in the 1970s.
In this groundbreaking study, researchers reviewed radio occultation data collected during 13 close encounters between Juno and Jupiter, integrating the effects of zonal winds into their analysis.
“Radio occultation enables us to peer through Jupiter’s dense, opaque atmosphere to understand its internal structure,” the researchers elucidated.
“During the occultation experiment, Juno transmits radio signals to NASA’s Deep Space Network on Earth.”
“As these signals traverse Jupiter’s electrically charged ionosphere, they experience bending and delay.”
“By measuring the frequency changes caused by this bending, we can derive the temperature, pressure, and electron density at various atmospheric depths.”
The research concluded that Jupiter is approximately 8 km narrower at its equator and 24 km flatter at its poles.
“Including the effects of zonal winds significantly diminishes uncertainty in our understanding of Jupiter’s shape,” the researchers noted.
“At a pressure level of 1 atmosphere, we’ve determined a polar radius of 66,842 km, an equatorial radius of 71,488 km, and a mean radius of 69,886 km, which are smaller by 12 km, 4 km, and 8 km than previously estimated, respectively.”
For more details, view the findings published in this week’s Nature Astronomy.
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E. Galanti et al. Jupiter’s Size and Shape. Nat Astron published online on February 2, 2026. doi: 10.1038/s41550-026-02777-x
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Source: www.sci.news
