Jupiter spins so quickly that it bulges around the middle. Its equator is about 7% wider than its top-to-bottom diameter. This squashed shape is caused by its fast spin, what’s inside the planet, and strong winds.
Past measurements of Jupiter’s shape, taken nearly 50 years ago by Voyager and Pioneer, were uncertain by about 4 km and didn’t account for winds.
Now, NASA’s Juno spacecraft has collected precise new data, giving scientists a clearer picture of Jupiter’s true shape. It suggests that the solar system’s largest planet is slightly smaller and more “squashed” than previously believed.
Using radio occultation data from 13 Juno flybys and considering the effects of Jupiter’s powerful zonal winds, the team measured the planet’s shape with ten times more precision. They found Jupiter’s polar radius is 66,842 ± 0.4 km, its equatorial radius is 71,488 ± 0.4 km, and its mean radius is 69,886 ± 0.4 km. These are slightly smaller than older estimates, by 12 km, 4 km, and 8 km, respectively.
Jupiter was once twice as prominent with a supercharged magnetic field
In simple words, Jupiter is shaped a bit like a squashed ball; it’s about 5 miles (8 kilometers) slimmer around the equator and 15 miles (24 kilometers) flatter at the poles.
Study authors noted, “The results indicate that winds above the visible cloud tops are largely barotropic, showing minimal vertical variation.”
Radio occultation lets scientists peek beneath Jupiter’s thick clouds. Juno sends radio signals to Earth, and as they pass through Jupiter’s upper atmosphere, called the ionosphere, the gases bend and slow them down. By tracking these small changes, researchers can figure out the planet’s temperature, pressure, and electron density at different depths.
Pinning down Jupiter’s true size gives astronomers a cosmic measuring stick. With this sharper standard, they can better decode the shapes and atmospheres of giant planets orbiting distant stars when those worlds pass in front of their suns.
Authors noted, “The updated shape has important implications for interior structure models, supporting a metal-enriched and cooler atmosphere, thereby helping reconcile discrepancies between models, Galileo probe measurements, and Voyager-derived temperatures.”
“The refined radius profile also improves spatial referencing for pressure-dependent measurements, offering a more precise context for interpreting Jupiter’s atmospheric dynamics.”
Journal Reference:
- Galanti, E., Smirnova, M., Ziv, M. et al. The size and shape of Jupiter. Nat Astron (2026). DOI: 10.1038/s41550-026-02777-x
