|Artist rendition of collision between proto-Earth and Theia
The formation of Earths moon is however created by a different means. Very near the end of the formation of the Earth, and
now only proto-planets exist, there is theorized that a proto-planet named Theia lay within the orbit of the proto-Earth.
The orbit of both these proto-planets overlapped in many places, and the probability of collisions was a near certainty.
The proto-planet Theia was a Mars-sized proto-planet, thus having a lot of kinetic energy behind her. When the collision
occurred, it literally ripped a large chunk of the proto-Earths early crust and upper mantle. The impact caused nearly 100%
melting and planetary differentiation. The ejected material created an accretion disk around the Earth, and through gravitational
influence, formed our Moon. This event was known as the "Giant Impact Hypothesis".
This model explains why the Moon doesn't have a large iron core and why its mostly made up of silicate material.
|Artist rendition of the Gaint Impact Hypothesis
The current explanation for the Asteroid Belt is this. There was going to be the formation of another planet, namely the dwarf
planet Ceres, however there simply wasn't enough mass there for the material to gather and form into larger masses. This was
because of Jupiter, Mars and Earth "stealing" material from the region, and because of their gravitational pull.
The retrograde orbit of Venus is also explained by the Solar Nebular Theory. During the chaos of collisions during the
accretion age, the proto-Venus was impacted by a fairly large planetesimal in the "opposite direction", causing
a change in angular momentum. Therefore, it rotates in the opposite direction.
The formation of the Jovian Planets is different however. Solar Nebular Theory explains this as follows. The region closer
to the proto-Sun is described to be "rocky" in nature, resulting in the terrestrial planets. However, further out,
more hydrogen, helium, methane and various other gases accumulated. An in the same manner of gravitational pull, they accreted
and formed the Gas Giants.
The icy worlds of the Kiuper Belt is a region where semi-rocky and semi-gases, icy worlds formed.