Using data from NASA’s Juno spacecraft, planetary scientists have produced the most precise measurements of Jupiter’s size in half a century and found the Solar System’s largest planet is slimmer and flatter than long believed.
Hubble’s photo of Jupiter displays the ever-changing landscape of its turbulent atmosphere. Image credit: NASA / ESA / Hubble / Amy Simon, NASA’s Goddard Space Flight Center / Michael H. Wong, University of California, Berkeley / Joseph DePasquale, STScI.
“Jupiter’s shape, as understood until now, was derived by researchers from just six measurements made almost five decades ago by NASA’s Voyager and Pioneer missions, which sent radio beams from the spacecraft to Earth,” said Dr. Eli Galanti, a researcher at the Weizmann Institute of Science.
“Those missions provided a foundation, but now we got the rare opportunity to spearhead the analysis of as many as 26 new measurements made by NASA’s Juno spacecraft.”
“Just by knowing the distance to Jupiter and watching how it rotates, it’s possible to figure out its size and shape,” said Weizmann Institute of Science’s Professor Yohai Kaspi.
“But making really accurate measurements calls for more sophisticated methods.”
“Juno’s passing behind Jupiter provides an opportunity for new science objectives,” said Juno’s principal investigator Dr. Scott Bolton, a researcher at Southwest Research Institute.
“When the spacecraft passes behind the planet, its radio communication signal is blocked and bent by Jupiter’s atmosphere. This enables an accurate measurement of Jupiter’s size.”
“We tracked how the radio signals bend as they pass through Jupiter’s atmosphere, which allowed us to translate this information into detailed maps of Jupiter’s temperature and density, producing the clearest picture yet of the giant planet’s size and shape,” explained Maria Smirnova, a Ph.D. student at the Weizmann Institute of Science.
The researchers found Jupiter’s polar radius to be 66,842 km, its equatorial radius 71,488 km, and its mean radius 69,886 km — each falling short of previous estimates by 12, 4, and 8 km, respectively.
“Textbooks will need to be updated. The size of Jupiter hasn’t changed, of course, but the way we measure it has,” Professor Kaspi said.
“These few kilometers matter. Shifting the radius by just a little lets our models of Jupiter’s interior fit both the gravity data and atmospheric measurements much better,” Dr. Galanti said.
“We were in a unique position to use our state-of-the-art models for the interior density structure of Jupiter to show that the refined shape helps bridge the gap between the models and the measurements,” said Maayan Ziv, a Ph.D. student at the Weizmann Institute of Science.
Earlier measurements didn’t account for Jupiter’s powerful winds. By folding them into their calculations, the scientists resolved discrepancies that had lingered for decades.
“It’s difficult to see what’s happening beneath the clouds of Jupiter, but the radio data give us a window into the depth of Jupiter’s zonal winds and powerful hurricanes,” Professor Kaspi said.
The results appear in the journal Nature Astronomy.
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E. Galanti et al. 2026. The size and shape of Jupiter. Nat Astron 10, 493-501; doi: 10.1038/s41550-026-02777-x
