Why Pluto isneither a star nor a planet

박 인 규

How astronomers have come to conclude Pluto is a star and not a planet.

평촌

분원

- 박인

규06

123

http://100.naver.com/100.nhn?docid=154611http://en.wikipedia.org/wiki/Plutohttp://en.wikipedia.org/wiki/Pluto

A few years ago, we studied that there are 9 planets in the solar system and Pluto is 9th planet of the solar system. However, on August 25th, 2006, Pluto was excluded from Planets and classi�ed to a dwarf planet. Why could not Pluto be a planet?

�e solar system is made up of the Sun, planets, satellites, asteroid and other objects. �e Sun is the only star in the solar system. �e Sun contains 99.9% of the total mass of the solar system.

A star 1 is not just a big or bright orbit. A star is a massive ball of gas held together by its gravity. A star can shine itself. Also, stars do not move. Stars are very di�erent from planets.

Planets orbit stars and keep moving. A planet is a large and round object in space that moves around a star, for example, Earth, Mars and Venus are planets. Planets can not shine themselves, but re�ect the star’s light.

Satellites mean objects orbiting planets by the planet’s attractive force. Asteroids are objects orbiting stars and smaller than planets but bigger than meteoroids.

Pluto had been classi�ed to planet until 2006. Pluto was discovered by Clyde William Tom-baugh 2 on February18th, 1930. Rowell and Tombaugh found out that Uranus’s orbit changed by little force. Later, it came to light that it was the mistaken observation. Anyway, Tombaugh calculated where does force came out and found Pluto. When people discovered Pluto, with this, Pluto became the only planet discovered by Americans. When people �rst knew about Pluto, they thought Pluto was as big as Earth. �is confusion came out because of Charon.

Charon and Pluto were very close, so that time’s observation technology could not distin-guish between Charon and Pluto. Also, Pluto’s surface is made by methane ice. So it re�ects sunlight a lot and looks bigger than it is. People named it a�er the Greek god’s name, Pluto, because it was not bright as they predicted. Pluto's apparent magnitude averages 15.1, bright-ening to 13.65 at perihelion. Its diameter is 2306km that is just one out of ten with Earth’s 3 diameter. Pluto’s mass is 1.3*10^22kg and volume is 7.15*10^9kg. Pluto is made by ice and stone, and its atmosphere is methane and nitrogen. Its average degree is -248 Celcius. It doesn’t have a ring but have 3 moons; Charon, Nix and Hydra.

456

http://en.wikipedia.org/wiki/Plutohttp://www.donga.com/fbin/output?n=200608260101http://en.wikipedia.org/wiki/Pluto

A�er Pluto was discovered and classi�ed as a planet, it was always under debate. Scientists argued whether Pluto was planet or not. Finally, Pluto was excluded from planets in 2006.

In my opinion, it was a right decision to classify Pluto as a dwarf planet. Pluto’s remaining classi�ed as a planet can bring more confusions than its being excluded. If Pluto is remained as a planet, it could bring a lot of confusions. If Pluto is planet, Ceres, charon, and Xena have to be classi�ed as planets as well. Observation technology is developing fast. It is clear that scientists will discover more objects that are bigger and more suitable 4 to be a planet. �ey announced that they may �nd more objects in Kuiper belt. If we admit all objects that are bigger than Pluto, it will bring a big confusion and cause the tottering of the solar system. Suppose that there were 20 planets in the solar system. You had to study the information about 20 planets. It would annoy students. Also, the discovery of Pluto came from a mistake. In fact, Pluto is too small to a�ect Neptune’s orbit. However, there are many negative points too. Excluding Pluto from planets stirs confusion. Pluto had been regarded as a planet for half century. All people studied that Pluto was the farthest planet from the sun in the solar system. People could not accept it easily. Also, all the data written before 2006 became wrong. Also, Pluto was the only planet discovered by Americans. It could make con�ict between European and American astronomers.

Pluto 5 has satellites, and is orbiting the Sun. It seems that Pluto has all the conditions to be a planet. Why did scientists exclude Pluto from a group of planets?

First of all, Pluto can not shine itself so it is not a star. But why cannot Pluto be a Planet? Some people think that Pluto was excluded from planets because it was too small and out of orbit. It is the wrong fact.

In fact, until 2006, Pluto satis�ed the conditions to be a planet. However, scientists found Kuiper belt. �e Kuiper belt is situated from about 30 to over 50 AU from the Sun, past the planet Neptune. �is belt consists of a minimum of 70,000 bodies of ice and rock that slowly orbit the sun. Scientists found a object name Xena at Kuiper belt.

Xena6 satis�ed conditions to be a planet and was even bigger than Pluto. Some people said they had to recognize Xena to be 10th planet of the Solar system. But scientists predicted that

they would �nd more and more objects that satisfy the conditions to be a planet because astro-nomic technology is developing fast. So they decided to change the conditions to be a planet.

�ey made 3 new conditions to be a planet. First, the object must be in orbit around the Sun. Second, the object must be massive enough to be a sphere by its own gravitational force. More speci�cally, its own gravity should pull it into a shape of hydrostatic equilibrium. �ird, it must have cleared the neighborhood around its orbit. Pluto satis�es the �rst and second conditions but failed to meet the third condition. �us, Pluto was classi�ed as a dwarf planet and named 134340.

In August 24th 7, 2pm at Czech Republic, 424 astronomers voted and classi�ed Pluto as a dwarf planet. American astronomers disagreed with the decision. �ey said they could not admit it.

Space is too big for human to understand. It seems ridiculous that humans classify enor-mous space. But we need to investigate space more and make it advanced. It starts step by step. In this sense, classifying Pluto as a dwarf planet means human technology has developed a lot for last years and humans can think more logically than before.

Reference

Mc.Dougal Littel space science ; chapter 2 Earth,Moon, and Sun

Mc.Dougal Littel space science ; chapter 3 Our solar system

Mc.Dougal Littel space science ; chapter 4 Stars, Galaxies and the Universe

The King�sher Science Encyclopedia ; King�sher publication Plc. p18~p39

평촌

분원

- 박인

규08