Planetology

PLANETOLOGY

Planetology is the branch of astronomy that deals with the physical features of the planets. Planetology studies include the origin and composition of the planets, and the solid bodies of comets and meteors found in the solar system.
Comet, Asteroid, and Meteor
An asteroid and a comet are very similar, and yet at times they are unique and easily distinguishable from each other. An asteroid and a comet are both a small solar body system, rotating around the sun. An asteroid consists of rock and metal, and may have some organic compound. Although it is quite like the comet, an asteroid does not have the visible coma of a fuzzy outline that a comet does. A comet is composed of dirt and ices, it is characterized by a fuzzy outline and tail that is visible when it is close to the sun, and when it is far from the sun, it is difficult to distinguish between an asteroid and a comet (NASA, 2013)
A Shooting Star
What has been and continues to be referred to as a shooting star, is not a star, but a meteoroid that burns up as it passes through the Earth’s atmosphere. They are objects as small as a piece of sand, called interplanetary sand, and they can be as large as a boulder which is called an asteroid (Cain, 2009). A meteoroid becomes a meteor when it strikes the atmosphere and leaves a bright tail line trailing it. , caused by the ram pressure of the meteoroid, not friction, like many believe. When a meteoroid is larger, the streak in the sky is called a fireball, one that is so bright it can leave a streak in the sky lasting several minutes. A meteoroid that is able to survive its passage through the atmosphere, is referred to by astronomers as a meteorite (Cain, 2009).
Asteroid Belt
The asteroid belt is the region of the Solar System located roughly between the orbits of Mars and Jupiter. It is occupied by numerous irregularly shaped bodies called asteroids or minor planets. The asteroid belt is designated as the main asteroid belt to distinguish its adherents from other asteroids in the Solar System (LICENSE, 2013).
About half the mass of the belt is contained in the four largest asteroids, Ceres, Vesta, Pallas, and Hygeia. They have mean diameters of more than 400 km. and the asteroid belts only dwarf planet, Ceres, is about 950 km in diameter. The asteroid material is so thinly distributed that several unmanned spacecraft’s have damaged it. Regardless of the damage, there are large asteroids still colliding to form asteroid families having similar orbital characteristics and composition. Within the asteroid belt, individual asteroids are categorized by their spectra, with most falling into three basic groups: carbonaceous, silicate, and metal-rich (LICENSE, 2013)
Kuiper Belt
Discovered by the Hubble Space Telescope in 1992, the Kuiper Belt was named after the Dutch-American space scientist Gerard Kuiper (1905–1973, who first advocated its existence. . The KBOs are thought to be “ice dwarfs”. Eris and Pluto are the largest objects in the belt to date.
Many comet pas through this belt at the furthest point from the Sun, suggesting that their lives begin there. The Kuiper Belt probably scatters at about 10 billion mile from the Sun, beyond that, solar nebula was too thin to form even ice dwarfs. It is believed that the Kuiper Belt is the home of comets orbiting the sun.
Occasionally the orbit of a KBO will be disturbed by gravitational interactions with giant planets causing the object to take up an orbit that crosses into the inner solar system. The Kuiper Belt extends from about 30 to 55 AU and is populated with hundreds of thousands of icy bodies, larger than 62 miles across, and an estimated trillion or more comets (NASA, 2013).
Oort Comet Cloud
The Oort Comet Cloud is a huge spherical shell of comet surrounding the solar system. This cloud occupies a distance of space close to 93 million miles, and its outer extent is believed to extend so far out that the nearby stars have a greater influence than the sun’s gravitational pull. It is estimated that the Oort cloud contains 0.1 to 2 trillion icy bodies in its solar orbit. There are times when a solar event occurs in bodies of the outer region, resulting in the object falling into the inner solar system as a long-period comet. These comets have very large, eccentric orbits, and take thousands of years to circle the sun. It is documented that this has only been observed in the inner solar system and recorded once (Green, 2013).
Oort has short period comets taking less than 200 years to orbit the sun and they travel in the same plane the majority of planets orbit. It is believed they come from a disc-shaped region known as the Kuiper Belt and named after the astronomer Gerard Kuiper. The objects in the Oort cloud and in the Kuiper Belt are believed to be remnants from the formation of the solar system about 4.6 billion years ago (Green, 2013).
Comets
Comets are icy objects from the outer solar systems that inhibit the regions of the Kuiper Belt, and the even further distant Oort cloud. Visible only from Earth in their elliptical orbit as they are brought closer to the Sun at one end. When comets fall toward the inner solar system its surface is heated by the Sun, and ice blow the crusts heats up and evaporates, causing jets of water and dust to burst out a huge cloud around it, called the coma. Some of the projectile material may form a tail or two. The tail always points away from the Sun, so it follows the coma and central nucleus of the comet while it approaches the inner solar system, always leading the way back to the outer region once the comet past perihelion (its closet point to the Sun). Comets fall into two categories: Long-period comets (taking 200+ years for orbit) originate from the Oort cloud and appear without warning. Bright comets typically have long periods, and unpredictable. Short-period comets (taking less than 200 years) originate from the Kuiper Belt, possibly began as a long period comet having a distant orbit disturbed by the gravitational field from one of the giant planets. These brightest and most famous of these comet is Haley’s comet
Shepherd Moons 'Shepherd ' moons are the small moons orbiting the outer edges of planetary rings or between the gaps of the rings. A planetary ring is a ring of dust and small particles orbiting around a planet in a flat disc-shaped region. The most spectacular and famous planetary rings are those around Saturn, but all of the solar system 's gas giant planets, which are Jupiter, Saturn, Uranus, Neptune, possess their own ring system. Examples of shepherd satellites include Saturn 's moons Prometheus and Pandora that shepherd which shepherd Saturn’s narrow, outer F ring (questions and answers, 2005).
The gravity of the shepherd moons serve to maintain a sharply defined edge to the ring; material, that drifts closer to the shepherd moon 's orbit is either deflected back into the body of the ring, ejected from the system, or accreted onto the moon itself (questions and answers, 2005).
Jovian Planets
All of the giant planets in our solar system have rings: Jupiter, Saturn, Uranus, and Neptune. Jupiter 's ring is thin and dark, and cannot be seen from Earth. Saturn 's rings are the most magnificent; they are bright, wide, and colorful. Uranus has nine dark rings around it, and Neptune 's rings are dark with a but contain a few bright arcs. (m. teachastronomy, 2013).
Jovian Planets are much larger than terrestrial planets, they have a larger gravitational pull(Bennett, Donahue, Schneider, & Voit, 2012). More mass means a Jovian planet has a much deeper gravity well so it can hang onto more moons. The gravity of massive planets can grab an asteroid orbiting the Sun and change the orbit of the asteroid enough that it orbits the Jovian planet for millions of years, but the orbit may be gravitationally unstable enough that the asteroid can escape if and when it gains enough angular momentum and energy

Works Cited
Bennett, J., Donahue, M., Schneider, N., & Voit, M. (2012). the essential cosmic perspective sixth edition. San Francisco: Pearson.
Cain, F. (2009, January 27th). What is a Shooting Star. Retrieved from Universe Today Web site: http://www.universetoday.com/24216/what-i-a-shooting-star/#ixzz2bK8kOoMU free dictionary. (2013). definition. In t. f. dictionary, Dictionary. www.thefreedictionary.com.
Green, N. (2013, August). space: the Oort cloud. Retrieved from about.comWeb site: pace.about.com/od/comets/a/The-Oort-Cloud.htm
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m. teachastronomy. (2013, August). Ring-Systems-of-the-Giant-Planets. Retrieved from m.teachastronomy Web site: http://www.m.teachasyronomy.com/astropedia/.../Ring-Systems-of-the-Giant-Planets
NASA. (2013, April 26th). Solar System Exploration Home. Retrieved from nasa government: solarsystem.nasa.gov/SSE/Home/Planets questions and answers. (2005, August 12th). Retrieved from experts 123 web site: wew.experts123.com/q/what-are-shepherd-moons.html
The American Heritage. (2005). Science Dictionary Copywrite. The American Heritage Science Dictionary. Hpughton Mifflin Company.

Cited: Bennett, J., Donahue, M., Schneider, N., & Voit, M. (2012). the essential cosmic perspective sixth edition. San Francisco: Pearson. Cain, F. (2009, January 27th). What is a Shooting Star. Retrieved from Universe Today Web site: http://www.universetoday.com/24216/what-i-a-shooting-star/#ixzz2bK8kOoMU free dictionary. (2013). definition. In t. f. dictionary, Dictionary. www.thefreedictionary.com. Green, N. (2013, August). space: the Oort cloud. Retrieved from about.comWeb site: pace.about.com/od/comets/a/The-Oort-Cloud.htm LICENSE, C.-B.-S. (2013, August). Orbits. Retrieved from wikipedia org: http://www.en.wikipedia.org m. teachastronomy. (2013, August). Ring-Systems-of-the-Giant-Planets. Retrieved from m.teachastronomy Web site: http://www.m.teachasyronomy.com/astropedia/.../Ring-Systems-of-the-Giant-Planets NASA. (2013, April 26th). Solar System Exploration Home. Retrieved from nasa government: solarsystem.nasa.gov/SSE/Home/Planets questions and answers. (2005, August 12th). Retrieved from experts 123 web site: wew.experts123.com/q/what-are-shepherd-moons.html The American Heritage. (2005). Science Dictionary Copywrite. The American Heritage Science Dictionary. Hpughton Mifflin Company.