Final answer:
The primary factor responsible for the condensation of materials in the solar nebula to form our solar system is gravity. The collapse of the nebula due to gravitational forces led to increasing temperatures in the center and the formation of planetesimals from condensing particles in the cooler outer regions, which ultimately gave rise to the planets and moons.
Step-by-step explanation:
The materials in a nebula condense primarily due to gravity. As the vast cloud of dust and gas that constituted the early solar nebula began to collapse under its own gravitational pull, the material moved toward the center, becoming increasingly concentrated and heated. This increasing temperature caused the solid particles to vaporize but as the nebula continued to contract and rotate, it eventually flattened into a disk. The cooling of the nebula at distances away from the hot center allowed solid particles to condense, leading to the formation of planetesimals, which are the building blocks for the planets and moons we observe in our solar system today.
Over time, a significant amount of material was pulled into the very hot center of this disc, ultimately forming the Sun, while the remainder of material in the outer parts condensed into the various other objects of the solar system including planets, their moons, and various debris like asteroids and comets.