WASHINGTON, February 4, 2026, 12:16 EST
- New Juno data puts Jupiter’s equatorial diameter at 88,841 miles (142,976 km), about 5 miles (8 km) smaller than earlier estimates
- Jupiter’s pole-to-pole diameter is 83,067 miles (133,684 km), about 15 miles (24 km) smaller, sharpening how “flattened” the planet is
- Scientists used radio occultation during Juno flybys, a technique that reads how the planet bends and delays spacecraft radio signals
NASA’s Juno spacecraft has delivered the most precise measurements yet of Jupiter’s size and shape, showing the solar system’s largest planet is slightly smaller than scientists had thought for decades. The updated figures come from a study published this week in the journal Nature Astronomy. Reuters
The tweak is small in miles, but it matters because Jupiter’s radius is a basic reference number used to model the planet’s interior and its atmosphere. Those models feed into how scientists understand gas giants more broadly, including planets orbiting other stars.
The new analysis draws on radio occultation, a method that effectively “reads” a planet’s limb by watching how a spacecraft’s radio signal bends and slows as it passes through the upper atmosphere on its way back to Earth. NASA said the team used data from 13 Juno flybys and accounted for zonal winds — fast east‑west bands that can subtly shift the planet’s measured outline. NASA
Juno measured Jupiter’s equatorial diameter at 88,841 miles (142,976 km), about 5 miles (8 km) smaller than earlier values. Jupiter’s diameter from north pole to south pole came in at 83,067 miles (133,684 km), about 15 miles (24 km) smaller than previously estimated.
The planet is not a sphere, and the new data sharpen how squashed it is. Jupiter is about 7% larger at the equator than at the poles, compared with about 0.33% for Earth, scientists said.
The timing was partly orbital luck. Lead author Eli Galanti of Israel’s Weizmann Institute of Science said Juno only got the right geometry after the mission was extended, when the spacecraft’s signal could pass through Jupiter’s atmosphere during a behind-the-planet alignment; “Measuring how the signal changed” helped pin down the size and shape, he said.
Yohai Kaspi of the Weizmann Institute said, “Textbooks will need to be updated,” while stressing the planet itself did not shrink — measurement did. The earlier baseline leaned on a limited set of radio occultation experiments from NASA’s Pioneer and Voyager flybys in the 1970s. Space
Maria Smirnova, also at Weizmann, said the team tracked how Juno’s radio signals bend through Jupiter’s atmosphere to build temperature and density maps, producing the “clearest picture yet” of the planet’s outline.
Even for a planet this big, small numbers propagate. Galanti said, “These few kilometers matter,” because shifting the radius slightly can bring interior models into better agreement with gravity and atmospheric data.
The broader payoff extends beyond Jupiter. NASA said Jupiter’s radius is used as a calibration standard when astronomers model giant exoplanets, especially those detected when they pass in front of their host star, because small changes in assumed size can skew estimates of density and structure.
But nailing down the “size” of a gas giant has built-in uncertainty. Jupiter has no solid surface, and the measurement depends on how its upper atmosphere and winds shape the point where scientists define the planet’s edge, as well as how radio signals propagate through its ionosphere.
Juno, launched in 2011 and orbiting Jupiter since 2016, has been mapping the planet’s atmosphere, interior, magnetic field and magnetosphere. Jupiter is mostly hydrogen and helium and is so large that all the other planets could fit inside it, including more than 1,300 Earths, researchers said.
