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Competitive Examination Notes - 005

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Solar System - 02
Terrestrial planets are bodies which lie in solid state contrast to gaseous appearing of outer planets. Mineral composition consists mainly of silicates, iron and magnesium. Venus, Earth and Mars have an atmosphere where as Mercury and Moon is devoid of atmosphere. The outer planets are different from terrestrial ones mainly because of their size and composition. These planets are made up mainly of light emements hydrogen, helium, methane and ammonia. Density is about 1 gram per cc. Jupiter and Saturn consist essentially of hydrogen and helium in proportion very similar to Sun while Uranus and Neptune are richer in methane, ammonia and ice.

The most distant known body orbiting the Sun is the dwarf planet Eris, which was reported to have discovered in July 2005. Eris is currently about 97 AU from the Sun. Another planet like object in the outer solar system named Sedna is currently at 90 AU but will reach about 900 AU at the farthest point in its orbit, thousands of years from now. Comets known as long period comets, however, schieve the greatest distance from the Sun; they have highly eccentric orbits ranging out to 50,000 AU or more. A comet's period calculated as how long it takes to complete one revolution around the Sun. They are members of the Oort cloud, a spherial shell of comet nuclei that surrounds the flat plane of plabetary orbits at this enormous distance.
The Solar System is also home to two regions populated by smaller objects. The asteroid belt, which lies between Mars and Jupiter, similar to the terrestrial planets as it is composed mainly of rock and metal. Beyond Neptune's orbits lie trans-Neptunian objects composed most of ices, ammonia and methane. Within these two regions, five individual objects, Ceres, Pluto, Haumea, Makemake and Eris, termed dwarf planets have been revolving.

The Solar wind, a flow of plasma from the Sun, creates a bubble in the interstellar medium known as the heliosphere, which extends out to the edge of the scattered disck. The hypothetical Oort cloud, which acts as the sourse for long-period comets, may also exist at a distance roughly a thousand times further than the heliosphere. Six of the planets and three of the dwarf planets are orbited by natural satellites, usually termed 'moons' after Earth's Moon. Each of the outer plannets is encircled by planetary rings of dust and other particles. 
Next :- The Sun

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