The whole universe was created in such a manner that men often wonder at the beauty of everything in it. The sun, moon and everything outside of Earth were particularly under study for a long time because they are far and need time, investment, funds, research and technology before they can be reached. However, past explorations in the world outside the Earth have led to discoveries of the planets and other entities which make up the universe. This paper will discuss the solar system and the characteristics of the eight planets.

The solar system consists of Sun and the various bodies moving around it. These bodies consist of the eight planets, “dwarf planets,” satellites of the planets and small bodies such as asteroids, meteoroids and comets, and interplanetary medium (Arnett, “The Sun”). The solar system is an empty space. The bodies in it are so small when compared to the spaces between them. The eight bodies called planets are classified through their composition, size, position relative to the Sun, position relative to Earth, and history.

By composition, planets are categorized into terrestrial or rocky, and jovian or gas. Mercury, Venus, Earth and Mars belong to the terrestrial planets as they have rocky surface just like the Earth’s (Hamilton, “The Solar System”). These planets have rock and metal with high densities. They exhibit solid surfaces, no rings, few satellites and slow rotation. Jupiter, Saturn, Uranus and Neptune, on the other hand, are gas or jovian planets. They are called jovian because they exhibit gaseous nature just like Jupiter’s.

Their characteristics are the complete opposite of terrestrial planets: rings with lots of satellites, low densities, deep atmospheres, rapid rotation, and composed of hydrogen and helium (Arnett, “An Overview of the Solar System”). By size, the small planets Mercury, Venus, Earth and Mars have diameters less than 13000 km while the giant planets Jupiter, Saturn, Uranus and Neptune have diameters greater than 48000 km. By position relative to the Sun, Mercury, Venus, Earth and Mars belong to the inner solar system while Jupiter, Saturn, Uranus and Neptune make up the outer solar system.

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The boundary between Mars and Jupiter is an asteroid belt that separates the small planets from the giant ones. Pluto was recently considered as a dwarf planet (Arnett, “An Overview of the Solar System”). By position relative to Earth, there are inferior and superior planets. Inferior planets are those closer to the Sun than Earth, such as Mercury and Venus. Superior planets are those far from the Sun than Earth, including the planets Mars, Jupiter, Saturn, Uranus, and Neptune. Planets classified by history are categorized further into classical and modern.

The former includes Mercury, Venus, Mars, Jupiter and Saturn, and they were visible to the naked eye. Moreover, they have been known since the prehistoric times. The latter planets consist of Uranus and Neptune, which were both discovered in modern times. They can be seen with optical aid. There have been arguments regarding the issue that all eight planets should fall under the classical category (Arnett, “An Overview of the Solar System”). The Sun The sun is the largest object and the center of the solar system. The planets are drawn by gravity towards the sun, which makes planet to revolve around it.

In the mass distribution within the solar system, the sun has 99. 85% of all matter. It is also considered as the richest source of electromagnetic energy in the form of light and heat (Hamilton, “The Solar System”). It is an average star because there are other stars similar to it. At the present time, the Sun consists of 70% hydrogen and 28% helium, and the rest is composed by less than two per cent of metals. However, this composition changes since the sun converts hydrogen to helium. Moreover, conditions in the core are very extreme.

The temperature reaches an astounding 15. 6 million Kelvin while the pressure is 250 million atmospheres. The sun’s density at the core is greater than 150 times that of water (Arnett, “An Overview of the Solar System”). Through nuclear fusion reactions, the sun can produce an energy output of 386 billion megawatts. With each second, 700 M tons of hydrogen are converted into 695 M tons of helium. Five million tons of energy in the form of gamma rays travels towards the surface (Arnett). At the surface of the sun, the photosphere’s temperature is about 5800 K.

Regions in the surface known as sunspots are at 3800 K. These regions can be as large as 50,000 km in diameter. Researches showed that sunspots are formed due to interactions in with the magnetic field of the sun (Arnett, “An Overview of the Solar System”). Mercury Mercury is nearest to the sun among the other planets and also the eighth largest. Its proximity to the sun causes the illumination of Mercury’s disk to change when viewed with a telescope. Space explorations to the planet helped scientists in determining activities surrounding the planet.

Flybys of spacecrafts have also helped in mapping the surface of Mercury. During explorations, it was discovered that Mercury’s orbit is strange in such a way that when the sun and other bodies are observed at different longitudes, the sun moves and increases in size as it approaches the zenith. At which point it would stop and move towards the horizon again and its size appears to decrease. The stars in the sky move three times faster. Other observers from different places in Mercury would observe the same eccentric motions (Arnett, “Mercury”).

Venus Venus is the second planet closest to the Sun and the sixth of the largest planets. It is 108. 2 million km from the sun. Because it is the brightest planet, the Greeks called Venus the goddess of love and beauty. In fact, the features of the planet’s surface were names for female figures. Other than the sun and the moon, Venus is the brightest in the sky. It is also one of the inferior planets, as it is close to the sun. It is inferior planet because it depicts phases when viewed from the Earth’s perspective.

There have been more than 20 explorations to visit Venus. Through the use of radar, detailed maps of the surface were made (Arnett, “Venus”). Researchers have found out that Venus’ rotation is very slow. A day in Venus is equivalent to 243 days on Earth. Another thing that scientists and researchers cannot explain is the discovery that Venus “always presents the same face toward Earth when the two planets are at their closest approach. ” No one can explain if this is resonance effect or just a pure coincidence (Arnett, “Venus”).

Earth is the most suitable planet for life in the universe. It ranks third among the closest to the sun and the fifth largest planet. Event though spacecrafts are not necessary to study Earth, it was only in the twentieth century when maps of the entire planet were created. Moreover, pictures taken from outer space were useful in weather predictions and tracking hurricanes. Earth is primarily composed of iron, oxygen, silicon and magnesium, and has layers. These are the crust, upper mantle, transition region, lower mantle, D’’ layer, outer core and inner core.

In the whole solar system, Earth is the densest major body. Its surface is covered with water. It is the only planet where water exists as liquid form. The atmosphere consists of 77% nitrogen and 21% oxygen. Scientists assumed that there must have been large amounts of carbon dioxide when the Earth was formed (Arnett, “Earth”). Mars Mars, also called the Red Planet, is the seventh largest planet and the fourth closest to the sun. Extensive studies have been done on Mars, and certain explorations led to the argument that Mars can be inhabited by humans.

Mars is smaller than the Earth, but their surface area do not differ. Researches have come to the conclusion that large lakes or ocean possibly existed. There were also images of what appeared to be frozen sea that was liquid about five million years ago. If this was proven true, it would be a big advance in research. Though Mars was like Earth in that its carbon dioxide was used to form carbonate rocks, Mars did not have plate tectonics. Thus the planet cannot recycle carbon dioxide back into the atmosphere and cannot maintain greenhouse effect. This makes Mars colder.

Jupiter Jupiter is the largest planet and fifth closest to the sun. It is considered as the most massive even when the other planets are combined. In fact, 318 times of Earth’s mass will equal to the mass of Jupiter. It is also the fourth brightest object and was labeled the “wandering star. ” Its large moons were Io, Europa, Ganymede, and Callisto (Arnett, “Jupiter”). Jupiter consists mainly of hydrogen (90%) and helium (10%). Like Saturn, Jupiter has rings, but only fainter and smaller. Space explorations were hindered by the high levels of energetic particles.

It would be dangerous for an unprotected human being to come close to Jupiter (Arnett, “Jupiter”). Saturn Saturn ranks second among the largest planets, and is sixth among the closest to the sun. As a gas planet, Saturn is the least dense and looks flattened when viewed with a telescope. This is because Saturn exhibits swift rotation and fluid state. It consists mainly of hydrogen (75%) and helium (25%). Unlike the rings of other planets, Saturn’s rings are bright (Arnett, “Saturn”). These rings exist due to countless tiny particles that are always in motion (“Saturn”).

These particles may be composed of water ice and rocky particles. Until now, researchers were unable to found out the origin of Saturn’s rings (Arnett, “Saturn”). Uranus Uranus is the third largest and the seventh planet closest to the sun. It is the farthest planet than can be viewed without optical aid (Gierasch and Nicholson). It consists of hydrogen (15%) and a little helium, and composed of rock and ices (Arnett, “Uranus”). Its atmosphere is made up of hydrogen (83%), helium (15%), and methane (2%). Uranus is considered as “a giant ball of gas and liquid” (Gierasch and Nicholson).

Like the other gas planets, Uranus has rings that are dark and consist of large particles (Arnett, “Uranus”). The planet’s greenish color can be attributed to methane absorbing red light in the atmosphere. One unusual characteristic of Uranus is that it is tipped on one side. Researchers assumed that this might be the result of Uranus colliding with another planet-sized body (Hamilton, “Uranus”). Neptune After Pluto, Neptune is the farthest from the sun and the fourth largest planet. In composition, Neptune is similar with Uranus. It consists of 15% hydrogen and a little helium.

Its blue color is also attributed to methane absorbing red light. Moreover, compared with other planets’ winds, Neptune’s winds are the fastest (about 2000 km/hr) (Arnett, “Neptune”). Explorations discovered a dark area in the planet’s surface which resembled a hurricane. This was called the Great Dark Spot. However, it disappeared in 1994 (Smith). The solar system consists of the Sun and the planets, along with their satellites, dwarf planets and other entities including asteroids, comets and dust. The sun is the center of the solar system, and is considered an ordinary star.

Mercury, Venus, Earth and Mars are planets that are categorized as terrestrial, small and inner planets while Jupiter, Saturn, Uranus and Neptune are gaseous, giant and outer planets. Mercury and Venus are inferior planets because they are closer to the sun than Earth while the rest of the planets are superior because they are farther from the sun. Classical planets, or those that have been known since prehistoric times, include Mercury, Venus, Mars, Jupiter and Saturn. Only Uranus and Neptune were discovered during modern times. However, there were arguments saying that all planets are classical.

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