At such a high pressure, even hydrogen atoms become so crushed that there is no room for the proton of a hydrogen nucleus to hold its electron. As a result, the protons are packed together and the electrons flow among them, hopping from proton to proton. This is how electrons flow in metals. That is why hydrogen under this level of pressure is known as metallic hydrogen. Physical properties of metallic hydrogen are quite different from molecular hydrogen even when it is sluggish under high pressure.
Metallic hydrogen appears more like mercury.
Inside this thick layer of metallic hydrogen, there may be a solid core made of silicate and ice. The size of this core is difficult to estimate. It could be several times larger than the Earth. However, it still represents a very small fraction of its total volume. One striking discovery by the Voyager is the existence of a thin ring surrounding Jupiter's equator.