Short answers, pulled from the story.
In planetary science, any material that has a relatively high equilibrium condensation temperature is called refractory. This distinction forms the foundation for understanding how planets form and what they are made of.
Super-refractory elements include rhenium, osmium, tungsten, zirconium, and hafnium with temperatures at or above 1700 Kelvin. These materials require extreme heat to transition from gas to solid under a pressure of 10 minus 4 bar.
Refractory material are also often divided into refractory lithophile elements and refractory siderophile elements based on chemical behavior rather than just temperature thresholds alone. Lithophile elements have an affinity for silicate minerals and tend to concentrate in the rocky crusts of planets while siderophile elements prefer metallic phases and migrate toward planetary cores during differentiation processes.
Volatile substances were largely absent from these regions due to the intense radiation and proximity to the young sun. The abundance of super-refractory and moderately refractory elements defines the physical properties of these worlds including their density and resistance to heat.
Giant planets like Jupiter and Saturn possess cores composed largely of these dense refractory substances. While outer solar system bodies contain more volatiles than their inner counterparts, they still retain significant amounts of rock-forming elements that help explain the gravitational dynamics and structural integrity of outer solar system objects.