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| Sunday, 17 October 2004 |
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Junior Observer |  |
| News Business Features Editorial
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Solar system : Family of planets
After the sun, the planets are the largest objects in the solar After the sun, the planets are the largest objects in the solar system. The straight lines lead from planets to their orbits. These are shown as blue loops centred on a tiny orange ball (the sun). The straight lines lead from planets to their orbits. These are shown as blue loops centred on a tiny orange ball (the sun). The hazy blue belt between the orbit of Jupiter and Mars shows the orbits of asteroids, or minor planets. The long orange loop shows the orbit of a comet that swings far into the solar system. When the sun was born from an immense cloud of gas and dust 4,600 million years ago, it is thought to have been surrounded by a disk of surplus material. Gradually, this disk formed into a number of smaller, cold bodies orbiting the Sun. And planets were born. So, the planets are considered the leftovers from the birth of the Sun. Groups of Planets Planets are grouped as interior planets or superior planets. Those nearer to the Sun are interior and those further away are called superior. They are also divided as Earth-like or terrestrial planets and giant planets. Mercury, Venus, Earth, Mars and Pluto are terrestrial planets. Jupiter, Saturn, Uranus and Neptune are the giant planets. Each giant planet also has at least two moons. If the smallest planet Mercury, was pictured as a pinhead, the largest planet Jupiter would be as big as a golf ball. On the same scale, the Sun would be as big as a beach ball. The hottest and coldest places Venus is the hottest of the Sun's planets. Space probes have measured the temperature on its surface as a scorching 460 degrees Celsius (950Fahrenheit). The reason is that Venus is surrounded by a dense atmosphere of carbon dioxide which traps the Sun's heat like a greenhouse. The coldest planet is distant Pluto, whose surface has a temperature of -230 degrees C (-490F). How stars and planets differ If you have been wondering whether there is a difference between stars and planets the answer is yes. Stars, which come in different sizes, are gigantic nuclear reactors composed of gas but planets can be either gaseous or solid. And unlike planets which shine only by reflecting light, stars which are hot bodies give out light of their own. The Earth we live in is a solid planet. But Jupiter is gaseous. You may be aware that nine planets orbit the Sun, which is a star in a gigantic collection of stars called the Galaxy. In order of distance from the Sun, they are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto.
Looking outward With no telescopes, early astronomers could see only the nearest planets to the Sun. They were Mercury, Venus, Mars, Jupiter and Saturn (not forgetting Earth!) It was only in 1781 that Uranus was discovered. Then in 1846 Neptune was discovered and later in 1930 Pluto came to be known.
Lord of the Rings No we are not talking about J.R.R. Tolkien's Lord of the Rings here. It's Saturn who is the topic because it has rings around it. Saturn's equator is girdled by a beautiful set of rings, made of countless ice-coated moonlets orbiting the planet. Saturn's rings measure 275,000km (172,000 miles) from rim to rim, yet they are only 100m (328 ft) thick. On the same scale of width to thickness, a long - playing record would be nearly 3km (2 miles) in diameter. Saturns' rings are probably the building blocks of a moon that never formed. Alternatively they could be the remains of a former moon that broke up. |
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