Until 2017, astronomers had assumed that the 'core' of the planet Jupiter would be dense, comparatively small ( compared with the planet's diameter ), and would be composed of rock and ices, possibly surrounded by a layer of 'metallic' hydrogen under extreme pressure.

But, in 2016, NASA's Juno spacecraft undertook a substantial set of very precise gravity measurements - and their analysis subsequently showed that the assumed model was very probably wrong.

Instead :

The Juno mission's measurements of Jupiter's gravity require a thorough revision of models of the interior of the solar system's largest planet. Doing so has proved to be a challenge given other constraints that must be satisfied, including atmospheric temperature and abundances of elements heavier than helium. Here we report models of Jupiter's interior that meet these constraints. Our models have a dilute core—a region substantially enriched in heavier elements—spanning 63% of the planet's radius. This unexpected feature challenges conventional models of the formation and early evolution of Jupiter."

Source : The Planetary Science Journal, Volume 3, Number 8

Future studies and measurements will be required to confirm the new hypothesis.

The findings also suggest that 'traditional' models for the cores of other 'gas giant' planets may need rethinking.

Note : The analysis also showed anomalies in the magnetic field of the planet - and it's now proposed that it may have an internal 'double dynamo' system - generating two distinct fields, This may have implications for Jupiter - radio auroraplugin-autotooltip__plain plugin-autotooltip_bigJupiter - radio aurora

Chance observations in 1955 logged strong radio frequency oscillations from Jupiter between the Kilometric (1000s metres) and Decametric (10s metres) wavebands. NASA's Juno spacecraft scanned Jupiter in late 2016 and made recordings of the emissions.

Also see : Planet formationplugin-autotooltip__plain plugin-autotooltip_bigPlanet formation

"The origin of planets is a vast, complex, and still quite mysterious subject. Despite decades of space exploration, ground-based observations, and detailed analyses of meteorites and cometary grains (the only space samples available in our laboratories),