NASA's Juno mission to Jupiter made the first definitive detection beyond our world of an internal magnetic field that changes over time, a phenomenon called secular variation. Juno determined the gas giant's secular variation is most likely driven by the planet's deep atmospheric winds.

The discovery will help scientists further understand Jupiter's interior structure - including atmospheric dynamics - as well as changes in Earth's magnetic field. A paper on the discovery was published today in the journal Nature Astronomy.

"Secular variation has been on the wish list of planetary scientists for decades," said Scott Bolton, Juno principal investigator from the Southwest Research Institute in San Antonio. "This discovery could only take place due to Juno's extremely accurate science instruments and the unique nature of Juno's orbit, which carries it low over the planet as it travels from pole to pole."

See: https://www.jpl.nasa.gov/news/news.php?feature=7406