What determines what group each planet will be placed in, when discussing its composition, is whether it is terrestrial and rocky or gas. Terrestrial planets are composed primarily of rock and metal and relatively high densities, slow rotation, solid surfaces, no rings and few satellites. Gas planets are composed primarily of hydrogen and helium, and generally have low densities, rapid rotation, deep atmospheres, rings and a lot of satellites. The terrestrial planets are Mercury, Venus, Earth and Mars. The gas planets are Jupiter, Saturn, Uranus and Neptune. Then there is Pluto which is in a group all its own.

The next method of classification is by size. The small planets are Mercury, Venus, Earth, Mars and Pluto. In order to be classified in the small planets group, the pla

Jupiter: Jupiter is more than twice as massive as the other planets combined.

A comet is a nebulous celestial body revolving around the sun. A comet is characterized by a long, luminous tail, but only in the segment of the comet's orbit when it passes closest to the sun. A comet is generally considered to consist of a small, sharp nucleus embedded in a nebulous disk called the coma. American astronomer Fred L. Whipple proposed in 1949 that the nucleus, containing practically all the mass of the comet, is a "dirty snowball" combined of ices and dust.

If some great force moved the Earth away from the Sun the oceans would freeze all the way to the bottom. They would be like solid rock. The air will liquefy then crystallize, leaving a layer of snow or ice to cover the whole planet. The sky gives us the seven days of the week because it is a period of seven days now in universal use as a division of time. It is of Hebrew or Chaldean origin and is mentioned as a unit of time in the Bible. The division of the lunar month into seven-day periods probably began as a celebration of the creation of the world in six days with the seventh day for rest. The Roman week was an eight-day period until 303 AD, when official recognition of the Christian religion made it necessary to celebrate the Sabbath every seventh day. The English names for the days of the week-Sunday (Sol), Monday (Moon), Tuesday (Tui, the Saxon Mars), Wednesday (Woden, or Mercury), Thursday (Thor, or Jupiter), Friday (Frygga, or Venus), and Saturday (Saturn)-come from Roman or Norse names for the planets.

Venus: Venus' orbit is the most nearly circular of that of any planet, with an eccentricity of less than 1%. It is also the brightest object in the sky except for the Sun and the Moon.

giant planets are sometimes referred to as gas giants, while Mercury and Pluto are sometimes called lesser planets.

Pluto: Pluto is about 2,320 km. (1,440 miles) in diameter. Charon is about 1,270 km. (790 miles) in diameter, making Pluto and Charon the planet-satellite pair closest in size in the Solar System.

Asteroids of the S type, related to the stony meteorites, make up 15 percent of the total population. Consisting of iron-nickel, they may represent the cores of melted, diverse planetary bodies whose outer layers were removed by impact cratering. A very few asteroids are probably related to the rarest meteorite class of all, the achondrites. These asteroids appear to have an igneous surface composition like that of many lunar and terrestrial lave flows. Scientists are puzzled that some of the asteroids have been melted, but others have not.

An asteroid is one of many small or minor planets that are members of the solar system and move in oval-shaped orbits, for the most part, between the orbits of Mars and Jupiter. The total mass of all asteroids in the solar system is much less than the mass of the Moon. The larger bodies are roughly spherical, but elongated and irregular shapes are common those with diameters of less than 160 km. Most asteroids may be binary, or have satellites of their own. Three-quarters of the asteroids visible from earth belong to the C type, which appears to be related to a class of stony meteorites known as carbonaceous chondrites. These are considered to be the oldest materials in the solar system, with a

Some common words found in the essay are:
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