I remember models of Jupiter going up to the Pioneer 10-11 days in the early 1970s where
astronomers thought that under the thick atmosphere full of clouds was a "crust" thousands
of miles thick with ice. In fact that was the general interior model for all the Jovian planets.

Jupiter's Core Bigger And Icier Than Thought

Red Orbit

http://www.redorbit.com/news/space/1602717/jupiters_core_bigger_and_icier_than_thought/

November 25, 2008

Jupiter has a rocky core that is more than twice as large as previously thought, according to computer calculations by a UNIVERSITY OF CALIFORNIA, BERKELEY, GEOPHYSICIST who simulated conditions inside the planet on the scale of individual hydrogen and helium atoms.... The simulation predict the properties of hydrogen-helium mixtures at the extreme pressures and temperatures that occur in Jupiter's interior, which cannot yet be studied with laboratory experiments. Applying techniques originally developed to study semiconductors, UC BERKELEY'S BURKHARD MILITZER, AN ASSISTANT PROFESSOR OF EARTH AND PLANETARY SCIENCE AND ASTRONOMY, calculated the properties of hydrogen and helium for temperature, density and pressure at the surface all the way to the planet's center.... The research was supported by the National Aeronautics and Space Administration and the National Science Foundation.