Astronomy: Planets and Solar System
This reflective treatise attempts to explain the stellar nebular theory and evidence to support the same. Besides, the paper explores the unique feature of terrestrial planets of Earth, Mercury, Venus, and Mars. The same explores these features in the Jovian planets of Jupiter, Saturn, Uranus, and Neptune. In addition, the treatise discusses minor members of the solar system, such as the comets, asteroids, and meteors.
The stellar nebula theory
The stellar nebular theory outlines cosmological evolution and the formation of the solar system. According to this theory, “dense and massive molecular hydrogen clouds formed the stars” (Stanley 23). These hydrogen clouds were unstable gravitationally; thus, facilitated coalesces of denser and smaller plods within. As a result, these clumps collapsed and formed the stars.
As opined by this theory, the stars formed produced protoplanetary gas, which formed a disk around them. This gas is thought to have given birth to the planetary system as a result of the cooling effect on the disk, which then formed small dust grains. These grains turned into rocks and coagulated into planetesimals. As a result of violent mergers, the planetesimals produced terrestrial planets (Stanley, 34).
The main evidence coined to support this theory includes the discovery of dusty and gaseous disks surrounding protostars. “It was observed that the dust particles within these disks grew in size over a period of time” (Stanley 45). Besides, scientific evidence indicates that embryo mergers would result in the formation of small round bodies.
The same feature is present in the solar system, which is characterized by the presence of different planets with different sizes depending on the distance from the star.
Besides, as of 2012, the scientists have discovered seven hundred and seventy-eight extrasolar planets thought to have formed from the nebular process as smaller embryos merger in a continuous process over a long period of time. The discovery opened doors to further exploration that led to the discovery of the dusty and gaseous disks surrounding protostars (Stanley, 39).
Terrestrial Planets of Earth, Mercury, Venus and Mars
The first four planets in the solar system are often referred to as the terrestrial planets. Reflective, these planets have a smaller diameter and are solid. Apart from the Earth and Mars, the other two have no satellites. Venus has the longest sidereal rotation period of 243 days, with the Earth having the least of 24 hours.
In this classification, Mercury has 59 days to complete a single sidereal rotation, with Mars having 25 hours. Mercury, Venus, and Earth are having an almost equal density of more than 5, with Mars having the least density of 3.9. The four planets have craters with Mercury having the most. Mars has a higher volcanoes than the other planets. However, this red planet lacks continental drift present in the other three (Lewis 67).
The “atmospheric chemical composition of Mars and Venus are very similar” (“Nature of the Universe: Terrestrial Planets,” par. 6). All the planets have layers of gaseous carbon dioxide with Earth having the least since photosynthesis absorbed most of the carbon dioxide gas.
Unlike the planet Earth, the others have no active volcanic activities. Actually, the presence of volcanic features on their surfaces is due to the “absence of continental drift” (“Nature of the Universe: Terrestrial Planets,” par. 7). Thus, due to their almost similar sizes, mass ratio, density, and revolution period, these planets are classified as terrestrial. However, they vary in composition, climate, and surface (Simon 45).
Jovian Planets of Jupiter, Saturn, Uranus, and Neptune
Often referred to as the Jovian planets, Jupiter, Saturn, Uranus, and Neptune have rings and are all “located outside of the asteroid belt” (“The Jovian Planets: Jupiter, Saturn, Uranus, and Neptune,” par. 8).
Reflectively, these planets share some features such as high mass, low density, are gaseous with some of these gases existing in solid form, rotates rapidly, are far to the sun, have a very strong magnetic field, and have very thick atmospheres.
Besides, the planets are characterized by the existence of many satellites in their field. In addition, these planets have a larger diameter and exist as fluid bodies, which are basically supported by hydrostatic equilibrium balancing gravity and pressure. Jupiter’s interior has a larger proportion of metallic hydrogen as compared to that of Saturn. However, Uranus and Neptune lack the metallic hydrogen component in their interior.
The rest of the interiors of these planets consist of ice and rocks. Interestingly, “Jovian planets have internal heat sources” (“The Jovian Planets: Jupiter, Saturn, Uranus, and Neptune,” par. 9). “They radiate more energy than they absorb from the sun” (“The Jovian Planets: Jupiter, Saturn, Uranus, and Neptune,” par. 12).
All the Jovian planets have large magnetospheres “filled with charged particles” (“The Jovian Planets: Jupiter, Saturn, Uranus, and Neptune,” par. 14) and cause series of defined bow shocks on the solar wind. Besides their own satellites, the Jovian planets have shepherd satellites in their ring systems.
Apart from that of Saturn, “the rings of the other Jovian planets are forward scattering” (Lewis 67). In fact, that of Saturn is usually dark and appears to have spokes.
Asteroids, Meteors, and Comets
Often referred to “as minor planets, Asteroids are metallic and rocky bodies revolving around the sun in the Asteroid belt” (Lewis 89). Their eccentric orbits sometimes wander into the regions between Jupiter and Mars. They vary in composition, orbit, and size. Factually, “Ceres is the largest asteroid with a diameter of 623 miles” (“Asteroids, Comets, and Meteoroids,” par. 4).
Asteroids exist in types C, S, and M. Type S is relatively light as compared to type C. Johann Bode discovered Asteroids in the 18th century. The widely accepted theory on the formation of asteroids states that “asteroids are pieces of matter that never coalesced to form a planet” (“Asteroids, Comets, and Meteoroids,” par. 6). However, they are of low density.
Commonly referred to as dirty snowballs, comets have long visible tail extending from their nucleus. There are two types of comets, that is, short-period comets and long-period comets. Ice and dust in the form of ammonia, water, methane, and carbon dioxide complete the structure of a typical comet. “Close to the nucleus of a comet is a bright cloud of gases and dust ejected from the nucleus” (Lewis 103).
Moreover, “meteorites are small chunks of stone that are capable of intersecting Earth’s orbit” (“Asteroids, Comets, and Meteoroids,” par. 10). Meteorites vary in sizes.
Meteoroid becomes meteor on invading the Earth’s atmosphere. However, when the same fails to disintegrate and fall on the Earth’s surface, then it becomes a meteorite (“Asteroids, Comets, and Meteoroids,” par. 19). Generally, meteors are believed to be originating scattering asteroids on collision with the asteroid belt. Asteroids are the largest among the three, with meteorites being the smallest.
Asteroids, Comets, and Meteoroids 2012.
Lewis, John. Physics and Chemistry of the Solar System, New York: Academic Press, 2004. Print.
Nature of the Universe: Terrestrial Planets 2010.
Simon, Seymour. Comets, Meteors, and Asteroids, New York: HarperCollins, 1998. Print.
Stanley, Ford. Notes on the nebular theory: in relation to stellar, solar, planetary, cometary and geological phenomena, California: Trubner, 1985. Print.
The Jovian Planets: Jupiter, Saturn, Uranus, and Neptune 2011.
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