content: While the majority of the matter is hydrogen, it's not all in gaseous form. A good portion of the internal structure is pressurized into "metallic hydrogen."  Gravitational measurements also suggest that there may be a rocky core with estimated 12 to 45 times the mass of our planet. Here's a diagram: https://upload.wikimedia.org/wikipedia/commons/thumb/b/b5/Jupiter_diagram.svg/1920px-Jupiter_diagram.svg.png