Using high-precision radio occultation measurements from NASA’s Juno mission and incorporating the effects of zonal winds, planetary scientists derived the shape of Jupiter with orders of magnitude less uncertainty, finding that the polar, equatorial, and mean radii are smaller than previous estimates made by NASA’s Pioneer and Voyager missions.
This visible-light image of Jupiter was created from data taken on January 11, 2017 using Hubble’s Wide Field Camera 3. Near the summit, a long brown feature known as the “Brown Barge” stretches 72,000 km (about 45,000 miles) from east to west. The Great Red Spot stands out in the lower left, and a small feature called Red Spot Junior (known to Jupiter scientists as Oval BA) is visible in the lower right. Image credits: NASA / ESA / NOIRLab / NSF / AURA / Wong others. / De Pater others. / M. Zamani.
“Jupiter, the largest planet in the solar system, is a nearly oblate spheroid, meaning it has a rapid rotation period of 9 hours, 55 minutes, and 29 seconds, so it is slightly flat at the poles and bulges at the equator,” said Dr. Eli Galanti of the Weizmann Institute of Science.
“This shape results from the balance between gravitational forces pulling radially inward and centrifugal forces pushing outward from the axis of rotation. As a result, for Jupiter, the equatorial radius is about 7% larger than the polar radius.”
“For an object of constant density, its shape is exactly ellipsoidal. However, Jupiter’s internal density profile differs significantly from the cloud level of about 1 bar, where the density is less than 1 kg/m.”3down to the depths where the density reaches several thousand kg/m3. “
“This causes a change in the shape of the planet from an ellipsoid on the order of tens of kilometers, which is expressed as a latitudinal change in the gravitational field.”
“Further changes in Jupiter’s shape are brought about by the strong zonal winds observed at cloud level.”
“These alter the centrifugal force, producing fluctuations of the order of 10 km, mainly at lower latitudes.”
Previously, Jupiter’s physical dimensions were based on data from six radio occultation experiments performed by NASA’s Pioneer and Voyager missions in the 1970s.
In the new study, the authors analyzed radio occultation data obtained during Juno’s 13 approaches to Jupiter and incorporated the effects of zonal winds.
“Radio occultation is used to ‘see’ through the dense, opaque clouds of Jupiter’s atmosphere to understand its internal structure,” they explained.
“During the occultation experiment, Juno will transmit radio signals to the NASA Deep Space Network on Earth.”
“When these signals pass through the electrically charged upper layer of Jupiter’s atmosphere, called the ionosphere, the gases bend and delay the signals.”
“By measuring the changes in frequency caused by this bending, we can calculate the temperature, pressure, and electron density of Jupiter’s atmosphere at different depths.”
The researchers’ results showed that Jupiter is about 8 km narrower at its equator and 24 km flatter at its poles.
“Incorporating the effects of zonal winds reduces the uncertainty by orders of magnitude in determining Jupiter’s shape,” the researchers said.
“At a pressure level of 1 atmosphere, we find a polar radius of 66,842 km, an equatorial radius of 71,488 km, and a mean radius of 69,886 km, which are 12 km, 4 km, and 8 km smaller than previous estimates, respectively.”
of findings Published in this week’s magazine natural astronomy.
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E. Galanti others. Jupiter’s size and shape. Nat Astronpublished online on February 2, 2026. doi: 10.1038/s41550-026-02777-x