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The theory that explains the origin of the Solar System is a little bit different than the Big Bang that is used to explain the beginning of the Universe. The beginning of the Solar System are explained by nebular hypothesis. It has been revised several times and the modern incarnation is called the Solar Nebular Disk Model (SNDM) or simply the Solar Nebular Model. The basic theory is explained below.
The nebular hypothesis states that stars are formed in clouds of interstellar gas. Each of these clouds is filled with ice and rock. The cloud thought to have formed this Solar System is generally referred to as the solar nebulae. Astronomers have proven that turbulence and agitation will cause these clouds to collapse, heating them up. This collapse and heating does not happen overnight; it takes thousands of years. The superheated gas and dust are pulled together to form a star. More gas causes the star to grow, while some of the material forms a solid ball. Once these solid balls are large enough, their gravity will attract more material. Eventually, these balls become large enough to be planetary cores. The objects that separate from the star early on become comets. This process takes millions of years. Overtime, each core accretes varying amounts of material and is shaped by impact events. This explains why each planet is different from the other.
The nebular hypothesis was first introduced in 1734 by Emanuel Swedenborg. It fell out of use for quite a while, but was revived several decades ago with a few revisions. Technology in the last 30 years have called it into question of late. Questions abound: why are the planets not on the same ecliptic plane, why are extrasolar planets so different from the ones in this Solar System, and why do some clouds not collapse are among them
As technology improves and astronomers are able to more closely study objects in the outer Solar System and discover new objects outside of our Solar System, the ability of the nebular theory to explain the origin of the Solar System comes under more intense fire. Changes have been made to attempt to explain some of the theory’s discrepancies, but all of the questions have not been answered yet.
University Today has a number of articles you will want to read including did our Solar System start with a little bang and new instrument could reconstruct planetary origins.
Check out the episode from Astronomy Cast about nebulae.