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| The Planets |
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| Planets are the largest objects in the solar system except for the sun. Unlike the sun, the planets do not produce their own energy. They reflect the heat and visible light produced by the sun. The four planets near the Sun - Mercury, Venus, Earth and Mars are called terrestrial (earth-like) planets because they are somewhat similar in size and composition to the earth. They appear to consist chiefly of iron and rock. The terrestrial planets and Pluto are the smallest planets. The earth has one satellite, Mars has two, and Pluto has one. Mercury and Venus have no satellites. |
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| Planets |
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| The outer planets - Jupiter, Saturn, Uranus and Neptune are called the giant planets or Jovian planets. They are mainly made up of hydrogen, helium and ice. Compared to the terrestrial planets, they contain little iron and rock. Each of the giant planets has several satellites. They also have rings around them. However, only Saturn's large, bright rings can be easily seen through a small telescope. |
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| All planets revolve round the sun in close elliptical paths. The nine planets in the order of increasing distances from the sun are given below: |
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| Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. |
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| Mercury is the smallest planet in the solar system and it is nearest to the sun. It is a bare, rocky planet not much larger than our moon. There is no water or air on mercury. By day it is hotter than the hottest desert. At night, it is freezing cold. The ground is covered with craters
formed by the crashing meteorites/rocks. |
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| Mercury |
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| Although only one third the size of the earth, mercury is very dense. The surface of mercury is similar to the earth's moon. Everything we know about mercury comes from one space probe, Mariner 10, which was sent in the year 1973, 1974 and again in 1975. With no atmosphere or water to erode them, the craters look as fresh as the day they were formed. |
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| The second planet from the sun is Venus. Venus is almost the same size as the earth, but it is surrounded by thick clouds of hot, poisonous gases. The surface of Venus is generally plain, dotted with mountains, valleys, craters and volcanoes, which may or may not be extinct. |
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| Venus |
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| It is the brightest object in the night sky other than the moon. It is visible in the early morning in the eastern sky or in the early evening in the western sky. It appears very bright because it reflects about 75 percent of the light, which it receives from the sun. |
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| This planet is also known as earth's
twin. The thick atmosphere on Venus has made the pressure in its atmosphere
90 times greater than on earth. Its atmosphere mainly consists of carbon
dioxide. Carbon dioxide traps the heat causing green house effect. The
temperature increases to 480oC. The atmosphere contains nitrogen,
water vapor and traces of gases like sulphur. Everything we know about this
planet is from the four Russian Venera probes. Like earth, Venus has a rocky mantle and a crust. Core contains iron, which may be partly in the molten stage. |
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| Earth is the only planet in our solar system, which is surrounded by oxygen, the life giving gas. It is the only planet to have large quantities of water. Earth's atmosphere contains oxygen, nitrogen, carbon dioxide and water vapour. |
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| Earth |
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| Earth is a medium sized planet with a thick atmosphere. The inside of the earth is still hot. The molten outer core of iron generates electrical currents which may be the cause of this planets magnetic field. The first primitive life forms may have developed in the oceans. |
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| It is called the red planet. The rocks on Mars are full of rusted iron. This is why the planet looks red. Huge storms of dust can also make the sky look pink. Mars has two very odd little moons called Deimos and Phobos. They look like giant potatoes and are pitted with craters. The space probe Mariner-9 that orbited Mars discovered channels that look like dried-up riverbeds. |
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| Mars |
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| Like earth Mars has a 24-hour day. Mars has a weak magnetic field. The Martian atmosphere is only one hundredth the density of earth. The presence of cracks and canyons indicate past earthquakes. In 1976, two Viking space probes were set out to investigate mars. |
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| Jupiter is a huge ball of gases. It is the biggest planet in the solar system. |
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| Jupiter |
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| Jupiter has a huge red spot on its
surface. Jupiter has more than 20 moons that spin around it. |
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| A ringed planet like Jupiter, Saturn is a giant ball of gases with a rocky core. |
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| Saturn |
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| From earth it looks as if three wide rings surround Saturn. In fact, these rings are made up of thousands of narrow rings. Each ring of Saturn is made up of dust and tiny bits of ice and rock.
Saturn has more than 30 moons, more than any other planet in the solar
system. A blanket of nitrogen gas surrounds Titan, the biggest of them. |
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| Uranus is the only planet in the solar system to orbit the sun tipped over on its side. The axes of most planets are almost perpendicular (at an angle of 90o) to the planets paths around the sun. But the axis of Uranus is tilted 98o from the perpendicular position, so that it is almost level with the planet's path around the sun. |
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| Uranus |
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| Uranus has at least 11 narrow rings. It
has more than 21 moons. |
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| Neptune is another gas giant. Some of the fastest winds in the solar system blow across its surface. |
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| Neptune |
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| The winds can reach speeds of over 2000
km an hour. Therefore, Neptune is said to be the windiest planet in the
solar system. Neptune has 13 moons circling it. |
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| Pluto is the ninth planet and is the most distant planet of all. It has one moon that is half as big as the planet. |
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| Note: The number of moons of the planets keeps changing i.e., with the imporvement in observing techniques, many new moons may be discovered. |
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| Pluto |
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| Some important facts and figures about the planets are given below: |
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