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Therefore the evolution of the solar nebula involved both the transportation of mass into the central proto-Sun region and the increased angular momentum in the planetary regions. This meant that most of the primitive cloud?s mass fell in to the proto-Sun?s region while the remainder formed the planets.

It is not only important to study the evolution of the solar nebula, but also the formation of the planets. There is a general consensus that once the solar nebula settled to rest that solid dust particles began to move toward the central plane of the nebula. It was at this stage that the planets began to form. There are two current theories that resulted in the development of the planets. The first theory suggests that the planets formed in a very basic process where dust particles accumulated into planetesimals which in turn grew to the present planets. The second theory proposes that planetesimals resulted from a gravitational instability in the gaseous portion of the solar nebula.

The first theory states process of planet formation began with the settling of dust in into the central plane of the nebular disk. Soon after, the first dust particles began to coagulate into small solid bodies. These bodies then accumulated through a collective gravitational instability in of the dust disk. The thin dust disk became more massive through continual sedimentation and resulted in its breakup into a large number of planetesimals. Through a process of random collisions these planetesimal continued to grow and accumulate mass. There are two possible extremes that ended this process of accumulation. The first involved runaway accreting where one object grows extremely large through the collection of all smaller planetesimals within its area. The alternative extreme would involve the uniform growth of a number of masses resulting in a many equal mass planetesimals. It is currently believed that the formation of the planets resulted from a combination of these two processes. The equal mass accumulation is presumed to have dominated during the early stages of planet formation while the run away accumulation is suggested to have taken over during the latter stages. However, there is one substantial problem with this explanation of the planet’s formation. The accumulation theory fails to take into account the rapid formation of the giant planets. By the slow process of coagulation, it would take much longer then the lifetime of the solar system to form the giant planets of Jupiter and Saturn. This incorrectness in the first theory led scientists to contrive the second theory.

The second theory of planetary evolution involves a gravitational instability of the gaseous portion of the solar nebula. It is suggested that if the solar system were massive enough then the instability would lead to the fragmentation of the gaseous nebula and the formation of giant gaseous protoplanets. This theory allows plenty of time for the formation of the very large planets Jupiter and Saturn. The one flaw of this theory is its contingency on a very massive planetary nebula, one much larger than ours. Because of this problem many cosmogonists have begun to doubt that the gaseous disk instability led to planet formation in our solar system.

Although many of the details on the theories of our solar system will most likely change in the near future, the fundamental concept of solar system formation appear to remain the same. The Sun and planets began forming approximately 4.56 billion years ago out of a solar nebula produced by the collapse of a rotating interstellar cloud of gas and dust. Following soon after, the terrestrial and Jovian planets eventually formed from the collision and accumulation of smaller planetesimals.

While there is significant evidence supporting the formation of the Sun and planets in this way, it is not likely that scientist will know with complete certainty about the solar system?s origin for some time. It is highly likely that the details in the theory of the solar system will change. With continued improvements in technology and significant advances in astronomical fields of observation, further understanding of our solar system will undoubtedly come. In recent years, the idea that the Solar System formed from the evolution of a primodial solar nebula, has received significant conformation. The use of satellites such as the Infrared Astronomical Satellite (IRAS) have detected disks of solid particles around several nearby stars, including Formalhaut, Beta Pictoris and Vega. The uses of satellites have provided scientists with most of the information they currently have on the system?s origin. Another source of information lies in our neighboring planets.

Investigations of the other planets in the solar system by means of interplanetary spacecraft have provided a wealth of data pertaining to the origin and history of the solar system. Through the observation of solar-type stars in the Galaxy, we can learn critical information about the properties of the interstellar cloud that collapsed to form our own solar nebula. It is likely that future explorations and observations will help to solidify our understanding of the solar system.

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