Astronomy. Solar System Formation Processes


For many years, different scientists have come up with varied ideas that explain the origin as well as the future of the world. This has not been the case with solar system. One of the main reasons is that most of the scholars had limited knowledge about the existence of the solar system. This was until the advent of heliocentrism philosophy which asserted that the sun was centrally positioned with the earth rotating around it. This marked the beginning of establishment of theories and ideas that explained the formation of the solar system. Kant, Swedenborg and Laplace came up with the Nebula hypothesis (Lee pp. 1591-1611). This theory was found to have numerous weaknesses leading to some scholars questioning its credibility. It is with this respect that different intellectuals have come up with varied ideas regarding the process involved in the formation of solar system and subsequent evolution. This paper aims at highlighting some of the established ideas as well as what is believed about the fate of the solar system.

Formation of the Solar system

Pre-solar nebula

Laplace, Kant and Swedenborg in their nebula theory argues that formation of the solar system came about due to gravitational disintegration of a facet of a massive molecular cloud. They argue that the facet underwent further fragmentation leading to formation of solid cores. It is from one of these fragments that the solar system emerged. An analysis conducted on ancient meteorites has shown presence of short-term isotopes which results from explosion. There have also been traces of short-lived stars. These findings led to an idea that numerous supernovae took place close to the sun during its formation. It is believed that formation of the sun may have resulted from a distress wave emerging from the supernova (Astronomy Online para. 2-7). The wave led to disturbance of the supernova resulting in creation of extremely dense regions. Subsequently, these regions collapsed forming the sun. Supernova is thought to have been formed from numerous short-term stars. Hence, the sun is said to have formed during star formation process in a vast region that had numerous stars.

Analysis of kuiper belt as well as anomalous materials corrected from the belt revealed that the sun was formed from a group of big stars which had their diameter ranging from 6.5 to 19.5 light years. The total mass of all stars that formed the sun is believed to be 3,000 times that of the present sun.

As the nebula fragmented, it rotated at a very high speed. During condensation process of the materials that were within the nebula, the atoms in them increasingly started knocking against one another. This led to their kinetic energy being transformed into heat. Most of the nebula materials collected in the middle leading to its center becoming hotter than the peripheries. Availability of numerous forces within the surface of the nebula led to it flattening. These forces included gravitational force, magnetic force, gas pressure and rotational forces. Accordingly, the central region of the nebula changed into a big star with potential hydrogen fusion. This is referred to as protostar. At this stage, the sun had not completely developed and was seen as a T Tauri star (Whitehouse pp. 236-257). Fifty million years later, pressure and temperature in the middle of the sun intensified triggering the hydrogen fusion process. This led to an upsurge of inner energy that was against gravitational contraction. Eventually, hydrostatic balance was attained. It is this process that led to formation of the current sun. This phase of sun formation is referred to as the main sequence. Being one of the stars, the sun is said to get its energy from hydrogen fusion that takes place in its core.

Planets formation

Present day planets are thought to have emerged from the solar nebula. During the formation of the sun, a cloud of dust and gas was formed. It is this gas and dust that collected forming the current planets. The process through which planets were formed is referred to as accretion. Scholars argue that the initial planets started as dust particles around the sun. As these particles continued colliding, they fused and formed huge bodies. Subsequent collision of these bodies led to formation of even bigger bodies referred to as planetesimals (Kominami & Ida pp. 43-56). Over the time, these bodies have continued colliding leading to increase in their sizes.

The temperature at the centre of the solar system did not allow for the formation of planetesimals with low melting points. It was difficult for elements such as methane and water to solidify in this region. Hence, the planetesimals that formed in these regions comprised of compounds that could withstand high temperatures. They comprised of metals such as aluminium, nickel and iron. It is the bodies formed from these hardy compounds that comprise the present planets such as Mercury, Venus, Earth and Mars (Goldreich, Lithwick & Sari 497). Compounds that formed the aforementioned planets are scarce in the world. Consequently, it was hard for these planets to gather more elements as they rotated around the sun. This is the reason behind why these planets are smaller in size compared to other planets.

During planet formation, they were engulfed within a disc of gas and dust. The gas was supported by pressure making it had for the planets and the dust to rotate around the sun at a high speed. It is this low speed that led to shift in angular momentum making the different planets change their axis. The rate at which planets changed their axis depended on the level of temperature within the disc that covered the forming planets. From an improvised model, it has been found that as the disk degenerated, the planets moved inwards and occupied their present positions.

The rest of the planets (Jupiter, Saturn, Uranus and Neptune) are formed of gas. These planets formed past the iciness line. This is the region between the axis of Mars and Jupiter where temperature can support solidification of icy materials. These planets are known as the Jovian planets. The planets are bigger in size compared to terrestrial planets (Mercury, Venus, Earth and Mars). It is believed that the compounds that led to formation of these planets were abundant in the universe. In addition, as the compounds collided, they clamped forming giant planets. In fact, 99% of the total weight rotating around the sun comprise of the Jovian planets (Fogg & Nelson 1195). As the frost region collected a lot of water which emanated from evaporation of icy compounds, its pressure went down. This made it possible for dust and gas particles in this region to rotate at a very high speed around the sun.

It became hard for the particles to be attracted towards the sun. Consequently, the particles collected beyond the frost line leading to formation of a giant planet. Subsequent accumulation of hydrogen gas by this planet led to its size growing bigger. Within 1000 years after its formation, the weight of Jupiter had surpassed that of Earth by 318 times. Theorists argue that Saturn formed later after Jupiter had already formed and consumed most of the available gas. This is the reason behind its relatively low mass compared to Jupiter.

Unlike the older and more firm stars, the sun is believed to have sturdy stellar winds. By the time Uranus and Neptune were forming, stellar winds on the surface of the sun had already blown away most of the materials that had fragmented during its formation. Therefore, there were limited materials for the two planets to accumulate. It is believed that the process of forming the two planets did not succeed and are termed as failed cores (Elmegreen 77). The time taken for their formation has not yet been identified with some scientists claiming that the two planets may have formed in a region that was close to the sun or some where between Jupiter and Saturn. As planetary shift was not necessarily towards the sun, the two planets are supposed to have later shifted to their present position after formation. Scientists claims that in ten million years to come, stellar winds within the surface of the sun will have blown out all the available particles. As planets grow in size by accumulating these particles, it will mark the end of planet growth.

Subsequent evolution

Initially, scientists believed that every planet was formed in its present axis. Nevertheless, this idea has significantly changed due to successive scientific revelations that have been established. There is a belief that significant changes have taken place in the solar system since its formation. For instance, there were numerous bodies in the core of the solar system and the outer region of the solar system was clouded than it is today. The Kuiper belt has also been found to shift farther from the sun.

Terrestrial planets

By the end of era of planet formation, the core of the solar system was made up of numerous planetary embryos that were of the same size as the moon. As these embryos orbited around the sun, they crushed with one another leading to some merging to form bigger bodies. This process took not more than a hundred million years. The present moon in planet Earth is thought to have come as a result of collision between these planetary embryos. Another crash led to the removal of the outer cover that engulfed planet Mercury. One of the drawbacks of this theory is its inability to account for the different terrestrial planets ended up settling in their present orbits. There are some scientists who have posited that terrestrial planets formed within the disc of dust particles which had not been blown away by stellar winds. As a result, energy of the terrestrial planets was reduced by gravitational force of the dust leading to each planet assuming a unique axis (Rybicki & Denis pp. 130-137). This theory has been criticized due to the fact that existence of such dust would have made it hard for the planets’ axis to be odd as they are today. Another theory posits that there was some gravitational force between the planets and other bodies that were present in the core of the solar system. As the planets shifted closer to these bodies, their gravities attracted the bodies leading to development of regions with higher density. This triggered gravitational pull on the planets slowing them down into their present axis.

Planetary Migration

The scientists who came up with the nebula theory believe that Uranus and Neptune are wrongly positioned in their present orbits. This is because the conditions present in these orbits can not allow for planet formation. As a result, the two planets are believed to have formed in a different region and migrated to their current orbits. The present conditions of the outer region of the solar system resulted from planetary migration of the outer planets. After Neptune, the solar system stretches to Kuiper belt, the dispersed disc and farther into the Oort cloud where comets are believed to have originated. The distance from these regions to the sun could not allow for the formation of planets. This is because the buildup process was low making it hard for the disc to gain enough weight to allow it consolidate into a planet. Initially, the Kuiper belt was closer to the sun. After establishment of the solar system, the axis of all the bigger planets gradually changed due to interaction between them and planetesimals that were still available (Wallace 43). Eventually, the resonance of the giant planets changed. Saturn was found to rotate around the sun once for every two rotations made by Jupiter.

The resonance led to surge of gravitational force that acted in opposition to outer planets. This force led to Neptune shifting its position beyond Uranus and settling in the region that was initially occupied by the Kuiper belt. As the giant planets migrated outwards, they forced most of the smaller frosty bodies to move inwards. In addition, as the planetesimals migrated inwards, they pushed behind all the planets they came across making their axis shift outwards. This was until they came across Jupiter. The high gravitational force in Jupiter made it hard for planetesimals to push it behind. Instead, most of them were propelled into more oblique axis while some were even forced out of the solar system. In the end, Jupiter shifted vaguely inwards. It is those planetesimals that were propelled to oblique orbits that led to formation of the Oort cloud (Wallace pp. 53-61). The present Kuiper belt and dispersed disc formed from planetesimals that were slightly dispersed by Neptune during its migration. On the other hand, the inner planets have been found not to undergo any significant migration since their formation. This is due to stability of their axis which resulted during the epoch of giant effects.

Era of heavy bombardment

The outer planets’ migration led to instability in gravitational force. Most of the asteroids were propelled into the core of the solar system. This led to the initial belt wearing off to its present low mass. The bombardment that took place four billion years ago is believed to have occurred due to this instability. Presence of cratering on the surface of the moon and Mercury is clear evidence that bombardment occurred. The crush between Jupiter and comet Shoemaker-Levy 9 in 1994 is good evidence that even today the planets collide (Duncan, Quinn & Tremaine pp. 1330-1337). This implies that the era of planet growth has not come to an end and there is high possibility that some planets will continue increasing in size and mass.


The aforementioned processes and evolutions give clear evidence that formation of the solar system has been a continuous process. Some of the recently witnessed impacts between the planets and comets indicate that the solar system still continues evolving. However, the sun has not been found to evolve since its formation. Scientists posit that the sun will remain in its current state until all the hydrogen in its core is fused to form helium. Once all hydrogen atoms on the surface of the sun are converted to Helium, the sun will embark on transformation from the main sequence. Scientific investigations have revealed that as hydrogen present in the core of the sun continues fusing, the light given by the sun continues becoming brighter. As hydrogen fusion takes place, temperature at the center of the sun increases hastening the fusion process. It is believed that in one billion years to come, the sun’s radiations reaching the earth surface will lead to increase in temperature to an extent that it will not support existence of any living organism. It will even be difficult for water to exist in liquid form. This gives an indication that the earth is gradually facing extinction. In many years to come, the conditions in planet earth will change and assume those experienced in Venus. It will be hard for the planet to support life leading to termination of life in planet earth.

Works Cited

Astronomy Online. “The solar system formation.” 2009. Web.

Duncan, Martin, Quinn, Thomas & Tremaine, Scott. “The formation and extent of the solar system comet cloud.” The Astronomical Journal 94.5 (1987): 1330-1337.

Elmegreen, Bruce G. “On the disruption of a protoplanetary disc nebula by a T Tauri like solar wind.” Astronomy & Astrophysics 80 (1979): 77.

Fogg, Martyn J & Nelson, Richard P. “On the formation of terrestrial planets in hot-Jupiter systems”. Astronomy & Astrophysics 461 (2007): 1195.

Goldreich, Peter, Lithwick, Yoram & Sari, Re’em. “Final Stages of Planet Formation”. The Astrophysical Journal 614 (10 October 2004): 497.

Kominami, Junko & Ida, Shigeru. “The Effect of Tidal Interaction with a Gas Disk on Formation of Terrestrial Planets”. Icarus 157.1 (2001): 43–56.

Lee, Typhoon. “New isotopic clues to solar system formation.” Rev. Geophys 17.7 (1979): 1591-1611.

Rybicki, Kacper Rafal & Denis, de Casrto. “On the Final Destiny of the Earth and the Solar System”. Icarus 151.1 (2001): 130–137.

Wallace, Gary Ernst. “Earth’s Place in the Solar System”. Earth Systems: Processes and Issues. Cambridge: Cambridge University Press, 2000.

Whitehouse, David. The Sun: A Biography. New York: John Wiley and Sons, 2005.

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