Jupiter measured slightly smaller by NASA's Juno mission

NASA's Juno spacecraft measured Jupiter's equatorial diameter at about 88,841 miles and its polar diameter at about 83,067 miles, both modestly smaller than earlier estimates, using radio signals that passed through the planet's atmosphere.

New, precise observations from NASA's Juno spacecraft show Jupiter is modestly smaller and more flattened than earlier estimates indicated. The measurements refine both the planet's equatorial and polar diameters and come from experiments conducted after Juno's mission was extended in 2021. Scientists used radio signals sent from Juno that passed through Jupiter's atmosphere when the spacecraft was briefly behind the planet from Earth's viewpoint. The refined sizes are important because Jupiter's radius is a key reference for models of its interior and atmosphere and for understanding its role in the solar system's formation. Key observations: - Juno measured Jupiter's equatorial diameter at about 88,841 miles (142,976 km), roughly 5 miles (8 km) smaller than previous estimates. - The north–south (polar) diameter was measured at about 83,067 miles (133,684 km), about 15 miles (24 km) less than earlier values. - The planet is more oblate than previously known, with the equator about 7% larger than the polar diameter, compared with Earth's 0.33% difference. - The measurement technique used radio signals transmitted as Juno passed behind Jupiter; changes to the signal revealed information about atmospheric composition, density and temperature. - Earlier size estimates were based on data from Voyager and Pioneer in the late 1970s; Juno has been orbiting Jupiter since 2016 after launching in 2011. - The study reporting these results was led by Eli Galanti of the Weizmann Institute of Science and published in Nature Astronomy. Summary: The refined diameters update the standard reference for Jupiter's radius, which feeds into models of the planet's internal and atmospheric structure. These measurements will inform ongoing analyses of Jupiter's composition and of how the planet influenced the early solar system.