1.Four major features provide clues:
(1) The Sun, planets, and large moons generally rotate and orbit in a very organized way.
(2) With the exception of Pluto, the planets divide clearly into two groups: terrestrial and jovian.
(3) The solar system contains huge numbers of asteroids and comets.
(4) There are some notable exceptions to these general patterns.
2. Gravity causes the early solar nebula to collapse. The solar nebula flattens and warms at its core as it revolves. Within the spinning disk, planetesimals (early planets) begin to form.
3. Because the center of the revolving disk had the least amount of centripetal force, the majority of the mass from the nebula cloud was drawn to it by gravity. The majority of the material was hydrogen gas that was subjected to extreme pressure, which heated it to a critical point, causing it to fuse with another hydrogen atom, resulting in the formation of helium and the birth of the sun.
4. Nebular Theory: argues that when the Sun formed in the nebula, it created planets, asteroids, and other bodies from a spinning disk of materials known as the accretion disk. Almost all revolve in the same direction on their axes. Venus and Uranus are moving backwards on their axes.
5. In the inner solar nebula, only dense materials could condense. The Jovian planets are really denser than the terrestrial planets. Gravity compresses terrestrial planets to a greater extent, causing them to become denser. The gravity of the Sun drew dense materials into the inner solar system.
