The solar system has a diameter of about 11,790 million km. Its planets can be easily grouped into two divisions:
1) Inner Planets. These planets (Mercury, Venus, Earth and Mars) are smaller in sizes but have high densities. They are also known as Terrestrial Planets.
2) Outer Planets. These planets (Jupiter, Saturn, Uranus, Neptune and Pluto) are big in sizes but have low densities. They are also known as Major Planets.
The type of life found on Earth appears to be a very rare phenomenon. Mercury and Venus are very close to Sun and are therefore very hot. The rest of the planets are very cold.
These planets revolve around the Sun in ellipse-like orbits. Their average speed is 22.7 km per second. The planets closer to the Sun move fast than those which are more distant from it.
There are sub-planets (satellites) revolving around the planets of the Sun. Moon is such a sub-satellite which revolves around the Earth. Jupiter has as many as 12 sub-planets. Only Mercury and Venus have no sub-planets.
The Earth is at a distance of 149 million km from the sun while the most distant planet Pluto is 5.793 billion km away. If we compare Sun to a ball of golf, the Earth will be a sand particle at a distance of 3.6 metres and Pluto another sand particle at a distance of 152.4 metres form the Sun.
There are billions and billions of stars like our Sun in this universe. The star closest to our Sun in Proxima Centauri.
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