The Formation of Solar System: The Solar Nebula Hypothesis - Literature review Example

The Formation of Solar System: The Solar Nebula Hypothesis Introduction Immanuel Kant, a philosopher from German hypothesized in the eighteenth century that the Solar System was formed from a huge revolving gaseous nebula gradually contracting and condensing (Sreepat 65). A Nebula is a huge cloud of gas, and perhaps particles of dust, held together by the mutual gravitational force of the particles making it. Such nebula, as we see them somewhere else in our Galaxy, is immeasurably larger as compared to the Solar System. Pierre Laplace, a French mathematical astronomer, expounded on the idea in 1796, and it was known as the nebular hypothesis (Sreepat 66). The nebula theory The solar nebula theory or the nebular hypothesis is the most common acknowledged model that explains the formation of the solar system. It was at first applied to only the solar system but now considered to hold true all throughout the universe. The solar system was formed about 4.5 billion years ago from a large spinning cloud of dust called nebula. It is within the nebula that stars are formed the sun being a large star created in one such nebula (Frank 475). Something, possibly the shock wave from an igniting supernova also known as dying star elicited the drawing together of dust particles to form a thick sphere-shaped cloud. The dust accumulation triggered a chain reaction. As the center of the cloud attracted more dust particles, its gravitational pull grew stronger. More dust was accumulated, and the cloud subsided in on itself. As this occurred, the speed of spinning cloud increased (Frank 476). The forces of rotation at the equator of the cloud vetoed dust down this plane being drawn in, making the cloud become flat like a disc spinning around a dense core. Formation of sun As more mass was built up at the centre of the disc, the temperature raised radically. In due course, there was sufficient energy to trigger nuclear reactions. Hydrogen atoms merged to produce helium, releasing large amounts of energy in forceful bursts. This marked the formation of the Sun though it would take approximately 1- 10 million more years for it to settle into the key sequence star acknowledged today (Karttunen et al.205). Formation of planets The planet, as well as the other extraterrestrial objects like asteroids, was formed in the flat plane of the whirling disc of dust. Both electrostatic forces and sticky carbon coatings made particles of dust stick together forming clusters, which eventually stuck together forming rocks. Mutual gravity made these rocks come together, ultimately to form planets in a process called accretion. During and after the Terrestrial planets were formed, there was a cataclysmic bombardment by the remains of rocky planetesimals that cratered these planets’ surfaces. The impacting material, together with extreme radioactivity as well as consequent gravitational concentration, generated adequate heat to melt as well as chemically separate the planets into three layers (crust, mantle, and core) as per Holton et al. (487). The Terrestrial planets’ atmospheres were created in this process and subsequently by outgassing from hot interiors of planets as well as from the impacting material. Between Mars and Jupiter, in the asteroid belt, the solar nebula temperature was lower so that water and carbon-rich minerals could unite in the forming of planetesimals. From Jupiter outward, temperatures were much lower making large amounts of frozen water accumulate with the rocky matter in the planetesimals. At colder temperatures, other ices formed, like methane and ammonia, giving those far-away planetesimals a mixed composition of ammonia, water, as well as methane ice saturated with a small quantity of rocky matter (Karttunen et al.206). According to Solar Nebula Hypothesis, rocky planets formed in the centre of the protoplanetary disk where the temperatures were very high to prevent condensation of ice, water and other materials into grains. This resulted in the coagulation of only rocky grains and later on into the creation of rocky planetesimals. Following small planetesimals formation, runaway accretion began. Growth hastens as mass builds up leading to the growth of bigger bodies by the destruction of minor bodies. This lasted approximately 10,000 to 100,000 years and ended when the biggest bodies exceeded about 1,000 km in diameter. Next, oligarch accretion started. Many hundred of the largest bodies called oligarchs continued to accrete planetesimals. They grew impacting each other and forming a bigger body. The outcome of the oligarchic phase was the formation of approximately 100 bodies of the size of the Moon to the size of Mars (Karttunen et al 207). The merger phase is the last that starts when the oligarchs became enormous enough to perturb one another causing their orbits to be disorganized. This lasted for about 10 to 100 million years forming some of the Earth-sized bodies. A number of the oligarchs are considered to have brought water to planet Earth. The resulting rocky planets finally settle into nearby stable orbits. Formation of the Earth System Within a fairly short time after solar nebula began contracting, the young Earth had gathered most of the materials that make it today. The growing Earth Matter attracted matter that collided with it, producing its kinetic energy in the form of heat. This energy, together with the energy coming from Earths gravitational contraction as well as radioactive nuclei emissions, heated up the interior of the Earth. In only some tens of millions of years, the Earth was molten; followed by chemical differentiation. The heaviest elements particularly iron, detached from the lighter elements, like silicon and oxygen (in the form of oxides of magnesium or iron and silicates) and submerged toward the center. The oxides and silicates rose forming the mantle that surrounds an iron-rich core. The lightest matters rose to the top solidifying as the crust (Holton et al.487). Approximately 4.5 billion years ago, the whole Earth was cooling although volcanic activity on the surface was severe. It is believed that during this time an atmosphere of those compositions not certain was created, possibly from the gases carbon monoxide, carbon dioxide, nitrogen, water vapor, hydrogen sulfide and hydrogen. These gases escaped from the interior during volcanic activity as the earth cooled. Moreover, the water condensed, forming the oceans. Evidence for the Nebular Hypothesis The original angular momentum as well as subsequent development of the collapsing nebula makes this hypothesis to provide a natural explanation for a number of basic facts concerning the Solar System: the planets’ orbits lie virtually in a plane, the sun being at the center, the planets all rotate in the same direction, and the planets typically rotate in the same direction with the rotation axes almost at right angles to the orbital plane (Holton et al.486). Shortcomings of solar nebula hypothesis According to the nebular hypothesis, all satellites and planets should rotate in the west-to-east direction in which the nebula was rotating. But Saturn’s ninth satellite called Phoebe was found to be rotating around Saturn in the retrograde direction. Later two other Jupiter satellites were discovered rotating in the east-to-west direction (Jaki 130). The hypothesis was objected by astronomer Kirkwood in the nineteenth century claiming that if any unstable state should set in the rotating nebula equatorial zone, such as was assumed to result in the ring detachment, it would constantly persist (Jaki 138). In other words, it would be not possible for rings to be detached apart from at particular intervals. Furthermore, if a ring ought to form, it could not at all condense to form a planet since expansion of the gases composed of as well as the tidal attraction of the solar nebula would overbalance its parts gravitation (Jaki 140). Works cited Holton, Gerald J, and Stephen G. Brush. Physics, the Human Adventure: From Copernicus to Einstein and Beyond. New Brunswick, N.J: Rutgers University Press, 2001. Print Jain, Sreepat. Fundamentals of Physical Geology. , 2014. Internet resource Jaki, Stanley L. Planets and Planetarians. Edinbrugh: Scottish Acad. Pr, 1978. Print. Karttunen, Hannu, Pekka Kröger, Heikki Oja, Markku Poutanen, and Karl J. Donner. Fundamental Astronomy. New York, NY: Springer New York, 1987. Internet resource. Shu, Frank H. The Physical Universe: An Introduction to Astronomy. Sausalito, Calif: Univ. Science Books, 1982. Print Read More