Did You Know

On 14 June 1968, the asteroid Icarus passed within 6 million kilometres of Earth. On 23 March 1989, the asteroid 1989 FC passed within 800 000 km of Earth, and on 9 December 1994, asteroid 1994 XM1 passed within 105 000 km. This latter asteroid is only about 10 m in diameter but it would have done a lot of damage had it hit Earth.

Some asteroids have already hit the Earth's surface. There is a one-kilometre-wide crater in northern Arizona that was made by an asteroid impact some 50 000 years ago. This asteroid was made of iron and nickel and was about 30 m wide. As recently as 1908, what is thought to have been a 100 000-tonne asteroid exploded in the Earth's atmosphere at an altitude of about 10 km with the force of a 20 to 30 megaton nuclear bomb. The explosion occurred over Siberia and the blast from the explosion flattened forests and burned an area about 80 km across. Many scientists believe an asteroid impact about 65 million years ago was responsible for the extinction of the dinosaurs on Earth. The asteroid created a huge circular depression called the Chicxulub Crater centred in Mexico's Yucatan Peninsula. The diameter of the crater is about 180 km.

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