sentence: Scientists think that solar systems are created out of a huge cloud of gas.
sentences_after: The process by which the solar systems are created is called the Nebular Theory. The spin of the planets around the Sun, and each around its own axis was first caused by the original gas cloud having different density in different places. The spin increased as an effect of the contraction under gravity. So did the flatness of the solar system overall shape.
concept_name: scientist
headings: Formation and evolution of the Solar System
categories: Solar System