Outline the process by which planets form as natural by-products of star formation?

Outline the process by which planets form as natural by-products of star formation, and explain how that process accounts for the overall properties of our solar system.Outline the process by which planets form as natural by-products of star formation?The planetesimal theory, also called the Nebula theory is the leading theory on the formation of the solar system.



It all started with a cloud of gas. Due to gravity the clouds started to shrink. In the core density and temperature became high enough so that nuclear fusion could start. The gas cloud became a stable star. This is the present state of our Sun.



Around the Sun a disk of gas and dust was left, containing about 1% of the mass of the Sun. In the inner part of the disk it was warm enough so that molecules like water, ammonia and methane tended to stay as gases, and did not produce grains and clumps and so on. And because they stayed in gas form the radiation pressure from the Sun and the solar wind pushed them outwards.



Around the orbit of Jupiter it was cold enough for ice to form. Here the gaseous molecules could condense into grains and lumps, that quickly accreted into planetesimals. The proto-Jupiter and proto- Saturn grew large enough to pull in great quantities of hydrogen and helium from the solar nebula.



The inner planets accreted from grains containing heavier atoms like oxygen and aluminium and silicon as well as iron and nickel and so on.



Consequently inside the ice limit at 5 AU only small, dense planets have formed, while outside there is matter enough to form the gas giants.



At this stage there were a dozen of proto-planets and quite a lot of comet-like, icy, small stuff. The proto-planets swept space clean with their gravitation fields and the comets rained on them. This also helped in making their orbits more circular.



But it was still a period with big collisions. For instance there are clear indications that the Moon was formed after a collision of the proto-Earth with another big object.



Nowadays, what is left over are zones like the asteroid belt, where Jupiter's perturbing gravity inhibited the formation of another planet. And also the Oort cloud, the region outside the orbit of Neptune, where dwarf planets like Pluto and Eris make their long orbits.Outline the process by which planets form as natural by-products of star formation?http://en.wikipedia.org/wiki/Nebular_hyp鈥?/a>