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Evolution of the planet
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At around 4600 million years old, the Earth is part of a planetary system known as the Solar System. This system is formed by the star named the Sun and eight planets, 166 moons, 5 dwarf planets, and billions of smaller objects (asteroids, comets, meteoroids, interplanetary dust). Since 1989, when the first planet outside the solar system was discovered, between 30 and 60 new planets are discovered every year, making a total of around 300 known planets in other solar systems to date.

The Solar System is located in the Orion Arm of the Milky Way galaxy. Galaxies are systems composed of stars, planets, gases, dust and dark matter, and the Milky Way is one of forty galaxies which form part of the so-called Local Group.

Eighth Anniversary Image of Hubble's
Hubble Site
The Milky Way, one of the largest galaxies in the group, has a barred spiral shape and an average diameter of 100,000 light years (one light year is equal to nearly 10 billion kilometres)and is composed of between 200 and 400 billion stars.

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