Dear All, I understand that one of the most popular theories concerning the origin of the solar system begins with cloud of gas and dust (called a nebula), assumed to be the remnants of a supernova; in order to explain elements such as iron and above. That this nebula begins to flatten into a spinning pancake shape with a bulge at the center, with the bulge forming the sun and with the various planets condensing out of the rest of the pancake. All of this I can understand and accept. However, why is the sun composed mostly of hydrogen and not the denser elements such as iron and above, which should have headed to the center of the solar system, due to gravitational forces, the same way they did when earth condensed? Is there any theory on why the sun does not contain the heavy elements and the planets the gaseous elements or or gas molecules?