The origins of the solar system
The solar refers to a system that is gravitationally bound comprises of the sun, the eight significant planets and other dwarf planets and the objects orbiting the sun such as the moons. It also consists of other smaller bodies like asteroids and comets, the planets’ satellites and the interplanetary medium. The planets include the Mercury, Venus, Earth and Mars which form the inner planets while the others from the terrestrial planets including Jupiter, Saturn, Uranus and Neptune (Chambers & Mitton, 2017). The majority of the mass in the system is the sun and Jupiter. All of these planets have nearly circular orbits that can be seen lying almost within ecliptic, an almost flat disc. In addition to these is another smaller population of bodies which comprises of centaurs, comets and dust clouds within the interplanetary medium which travel freely between the various regions. A stream of particles that are charged and flowing from the sun forms the solar wind and this create the helisphere which represent the point at which pressure emanating from solar wind is equivalent to another pressure from interstellar medium (Chambers & Mitton, 2017).
The history of the solar system can be traced to the Babylonians, who were the first civilization a theory on the planets and records exist of planet Venus motions dating as early as 7th –century BC. These people can be said to have laid the foundation for the modern astrology in the Western world (Chambers & Mitton, 2017). There are various theories that explains the origin of the solar system but heliocentrism was the first step towards coming up with a theory of formation of the solar system , and the earth was placed at the center of the system with the earth orbiting around it. The idea was being held for thousands of years but was only embraced by the close of the 17th century. The nebular theory was to emerge later explaining how the solar system was formed. It held that the formation of the solar system happened in about 4.6 billion year ago. It involved gravity pulling together intercellular dust and gas clouds of low density referred to as nebula (Chambers & Mitton, 2017). More specifically, the Orion Nebula which refers to an interstellar cloud in within which the star systems and planets were formed. The size of the cloud was initially various light years across, and a small cloud that was overly dense led to the beginning of contraction and the growth of the over-density. This produced a faster concentration, and the first cloud particles’ motions were random but nebula was able to have a net rotation.
As the gravitational collapse was happening, the speed of the rotation of the cloud was increasing gradually because of the conservation of angular momentum. The efficiency of the gravitational collapse was more pronounced along the spin axis, and this led to the collapse of the rotating ball into a thin disk of about 0.003 years, which is the solar nebula, which had most of the mass being concentrated around the center (Chambers & Mitton, 2017). The gravitational potential energy from the contracting cloud was turned into kinetic energy of all the gas particles. Therefore, the solar nebular’s temperatures were higher around the center where majority of the mass was collected. The collected mass formed the protosun, which is the gas cloud that was formed into sun. Temperature at the center then became so high, and reached to almost 10 million. There was a lot of violence from the atoms’ collision which led to nuclear reaction and at this point the central star – the sun – was formed and having 99.8 % the entire mass. Further collapse was averted by the increase of density and temperature toward the center of the mass and also the pressure and this resulted to a net force that pointed outward (Chambers & Mitton, 2017). The sun was therefore able to reach a balance between the internal pressure and the gravitational force after about 50 million years. Thin disk around the sun formed the other solar system bodies including the planets and moons, comets and asteroids. Around the sun where a temperature was quite higher, the heaviest metals formed solid grains that were also heavy through condensation. These grains are the various compounds including the titanium, aluminum, nickel, aluminum and the silicates that were relatively cooler. Away from the sun, the temperature of the disk was so low that it allowed the formation of hydrogen-rich molecules, by condensation into ices that were a bit lighter comprising of frozen methane and ammonia and water ice. This can explain the origin of solid seeds necessary for solid formation of the planet (Chambers & Mitton, 2017). In the process there emerged four categories of solar system ingredients which include the metals, rocks, ice and the light gases.
Considering the formation of the sun, it took place in the nebulae that was high density and coldest. Gravity could only lead to creation of the sun after overwhelming the pressure emanating from the gases in the cloud. A mass of about 100 solar gases or more was needed to collapse the nebula into the sun naturally. This could also explain why many stars can be seen to be in a cluster, where as the cloud of gasses and particles contracts, molecular cloud cires (Chambers & Mitton, 2017). The nebula could be of many types that are categorized as ionization nebula, reflection nebula and dark cloud nebula. The ionization nebula can be seen to glow because of the ultra-violet light which is emerging from the surrounding stars which raises their temperature and are normally pink or red since they have hydrogen. The reflection nebula involves dust particles that scatter and reflect light.
The formation of the moons involved the gasses or particles clouds that were contracted, spined, flattened and then heated forming smaller disks of various materials near the planets , the same process in which nebula was formed. In the jovian nebulae accretion and condensation happened which lead to creation of smaller systems around every planet (Milone & Wilson, 2008). The assembling of the planet and its moon took place independently simultaneously from same dust and rocks. The formation of the moons happened elsewhere and they were then captured. The planets absorbed some planetesimals and ejected others which helped in the cleaning up of the system. When the solar system had no more debris, the formation of the planets came to an end (Milone & Wilson, 2008).
Other theories emerged to try and solve the shortcomings of the nebula theory such as the tidal theory, the Chamberlin-Moulton model, Interstellar cloud theory, Hoyle’s theory and more. The theories focused on two-body concept in an attempt to find a solution for angular momentum challenge of the nebular theory.
References
Chambers, J., & Mitton, J. (2017). From dust to life: the origin and evolution of our solar system. Princeton University Press.
Milone, E. F., & Wilson, W. J. F. (2008). Solar system astrophysics: Vol. 1. New York: Springer.
