Exploring the interior of icy giant planets is not an easy task. Without more advanced technology, we won’t be able to use probes to make measurements on site, so researchers must rely on models. These models are based on what scientists know about the substances that make up these ice giants such as Neptune and Uranus.
However, we can’t rule out that these models might contain errors. For example, it was previously assumed that carbon always took the form of diamond under very high pressures. Carbon and hydrogen are among the most abundant elements in the universe and make up a large portion of Neptune and Uranus, for example, in the form of methane. The deeper one goes down toward the center of either of these planets, the more extreme the conditions become. Initially, more complex structures of carbon and hydrogen are formed and then, at the very center, there is a solid core.