The origin of Universe and planets has always been one of the greatest mysteries astronomers have attempted to uncover for decades and centuries. Nevertheless, until the present days, there is no common view on the origin of planets, although the process of their formation is relatively clear to modern scientists. In such a situation, arguments of scientists concerning the origin of planets are focused on two major approaches, which are the most popular in the modern science: the sequential-accretion scenario and the gravitation-instability scenario.
In actuality, neither of the aforementioned scenarios is taken for granted as the only correct scenario of the origin of planets, but still researches carry on and new scientific discoveries can help to find out the true origin of planets some day.
In this respect, it should be said that within a few decades views on the origin of planets have changed consistently. To put it more precisely, in the 1970s the process of formation of planets was viewed as a steady and determined process. Scientists believed that planets are formed in the result of the transformation of amorphous disks of gas and dust into planets and solar system. At this point, it is important to lay emphasis on the fact that scientists stood on the ground that solar systems are similar. As the matter of fact, scientists used the solar system, where the Earth is located, as the model for other solar systems.
However, in the course of the development of astronomy, scientists have found out that solar systems are not identical at all. In stark contrast they are very different to the extent that it is practically impossible to find two identical solar system. The discovery of such a diversity of solar systems revolutionized in a way the view on planets and solar systems as well as their origins. Instead of a well-structured and deterministic process, the process of formation of planets and solar system proved to be a chaotic process, in which specialists can hardly identify clear system common to all planets and solar systems. In such a situation, scientists can discover more and more new facts, specific for different planets and solar system, which can change their view on the origin of planets, because to their uniqueness planets and solar system have their specific features and characteristics that determined their formation.
Nevertheless, today, specialists have two scenarios of the origin of planets, which they believe to be the most probable, although both scenarios have their own drawbacks. First of all, it is worth mentioning the sequential-accretion scenario, according to which tiny grains of dust clump together to create solid nuggets of rock, which either draw in huge amounts gas, becoming gas giants such as Jupiter, or do not, becoming rocky planets such as Earth (Lin, 2008). At first glance this scenario is convincing and reliable enough to be accepted by the overwhelming majority of scientists. However, this scenario has a substantial drawback. In fact, if this scenario is true, the process of formation of planets is a slow process, but, in such a situation, gas may disperse before it can run to completion. Hence, this scenario cannot be fully applied as the only possible explanation of the origin of planets.
Alternatively, specialists develop a different scenario known as the gravitation-instability. According to this scenario, gas giants take shape in an abrupt whoosh as the prenatal disk of gas and dusk breaks up (Lin, 2008). This process replicates the formation of stars, but this scenario still remains arguable because it assumes the existence of highly unstable conditions, which may not be attainable. In addition, another substantial drawback of the gravitation-instability scenario is the recent finding of scientists who have discovered that the heaviest planets and the lightest stars are separated by a “desert”ť ”“ a scarcity of intermediate bodies. Hence, scientists make a conclusion that planets have a different origin from the origin of stars. In such a way, the gravitation-instability scenario is criticized by many specialists and this scenario is still not as popular as the sequential-accretion scenario. The latter remains the mainstream scenario in regard to the origin of planets, but, as it has been already mentioned before, this scenario is imperfect too.
Obviously, the problem of the understanding of the origin of planets lies in the complexity of the phenomenon researched by scientists, lack of knowledge and insufficient technical opportunities of modern scientists. In spite of a tremendous progress, human science is still unable to adequately explain the origin of planets. In this respect, it is possible to presuppose that the solution of the problem can be found when the modern science makes a consistent, change in its approach to the study of planets and solar systems because the study of planet formation lies on the intersection of astrophysics, planetary science, statistical mechanics and nonlinear dynamics. It proves beyond a doubt that all these branches of science need to be united efficiently to make a breakthrough toward understanding of the origin of planets.