Transcript: Some of the general principals that relate planets to each other are to do with planetary geology. For example, larger planets are more likely to have internal geological activity than smaller planets. This is simply due to the increased mass of a planet increasing the amount of pressure in its interior and increasing the amount of energy released from radioactive elements deep within the core. These radioactive decay processes release heat which melts the interior material which leads to geological activity. During planet formation, another process kicks in called differentiation. This is the method by which heavier elements and materials sink relative to lighter elements and materials. So when planets form and they are still molten, the physical principal of differentiation will leave the metallic substances, pure elements and compounds, to gravitate toward the center while the lighter rocks end up in the mantel and the crust.