Jupiter hasn’t shrunk, but our best measurement of it just did. Using fresh data from NASA’s Juno spacecraft, scientists say the solar system’s largest planet is slightly smaller and squatter than decades-old estimates suggested, reports Smithsonian Magazine. The revised dimensions, published in Nature Astronomy, trim roughly 15 miles off Jupiter’s polar height and about 5 miles off its equatorial width—hardly enough to threaten its status as king of the planets.
Still, “textbooks will need to be updated,” says study co-author Yohai Kaspi of the Weizmann Institute of Science in Israel, in a statement. Earlier measurements came from NASA’s Voyager and Pioneer missions in the 1970s, which used a technique known as radio occultation: spacecraft beamed radio signals through Jupiter’s atmosphere, and scientists inferred the planet’s size from how those signals were slowed and bent. Those measurements, however, didn’t adequately factor in the influence of Jupiter’s powerful winds, researchers say.
Juno, which has been orbiting Jupiter since 2016, changed that, explains Live Science. During passes in which the spacecraft slips behind the giant planet from Earth’s perspective, its radio signal is temporarily blocked and distorted by Jupiter’s atmosphere. “This enables an accurate measurement of Jupiter’s size,” says study co-author Scott Bolton of the Southwest Research Institute. Using 24 such measurements, the team now pegs Jupiter at about 83,000 miles from pole to pole and 89,000 miles across at the equator.