Jupiter's Size Recalibrated by Juno Mission

For nearly five decades, our understanding of Jupiter's size was based on just six measurements from the Voyager and Pioneer flybys. These early missions provided the benchmark figures that have been used in textbooks for half a century. The Juno spacecraft utilized a method called radio occultation, analyzing how its radio signals were bent and delayed as they passed through Jupiter's atmosphere to Earth. By taking 24 new measurements during these occultation events, scientists were able to refine the planet's dimensions with an uncertainty of just 0.4 kilometers. These precise figures are critical for modeling Jupiter's interior. A smaller radius helps scientists better align gravity data with atmospheric models, providing new insights into the planet's deep winds, which extend thousands of kilometers below the cloud tops, and its large, "fuzzy" core that is thought to be partially dissolved. The updated measurements confirm Jupiter is more oblate, or "squashed," than previously known, a consequence of its rapid, sub-10-hour rotation. The planet is about 7% wider at its equator than from pole to pole, a much more pronounced bulge than Earth's 0.33% difference. Refining Jupiter's dimensions has implications far beyond our solar system. The gas giant serves as the primary reference point for studying large exoplanets; more accurate data on Jupiter sharpens our understanding of planetary formation and the physics governing gas giants orbiting other stars. Juno's Gravity Science experiment achieved this precision by measuring minute Doppler shifts in radio signals exchanged between the spacecraft and NASA's Deep Space Network on Earth. These shifts reveal tiny variations in Juno's orbit caused by the planet's gravitational field, allowing scientists to map the distribution of mass inside Jupiter.