Transcription: Our Earth is but one small part of a vast system of planets, satellites, asteroids, meteoroids and comets that revolve around the Sun. Nine planets orbit the Sun and move in the same west to east direction. All of them except the outermost move in roughly the same plane. Mercury, then Venus, Earth and Mars are small planets that are relatively close to the Sun. They are called terrestrial planets and consist chiefly of iron and rock. Jupiter, Saturn, Uranus and Neptune are large gaseous planets. They probably contain little rock and iron but are made up of hydrogen, helium, ammonia and methane ...
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