Asteroid

Asteroids are small bodies that are believed to be the left over from the beginning of the solar system 4.6 billion years ago. They are rocky objects with round or irregular shapes up to several hundred km across, but most are much smaller.

More than 100,000 asteroids lie in a belt between Mars and Jupiter  which is called the Asteroid Belt. These asteroids lie in a location in the solar system where there seems to be a jump in the spacing between the planets. Scientists think that this debris may be the remains of an early planet, which broke up early in the solar system. Several thousand of the largest asteroids in this belt have been given names.

The chances of an asteroid colliding with Earth are very small, but some do come close to Earth, like Hermes (closest approach of 777,000 km).

Hermes isn't the only asteroid that has passed Earth. 99942 Apophis (previously known as 2004 MN4 and discovered by Tucker on June 19th 2004) is another near Earth asteroid that caused a small period of concern in December 2004 because observations showed a relatively large asteroid, probability that it would strike the Earth in 2029. Later on observations showed and improved the predictions which eliminated the possibility of an impact on Earth or Moon in 2029. However Apophis' close encounter in 2029 will pass through a gravitational keyhole which is a small region of space that if an asteroid were to pass through it, its course would change due to Earth's gravity and collide with Earth in its next orbital pass. This gravitational keyhole will set an impact for future on April 13 2036. Even though scientists predicted that Apophis will hit Earth in 2036, it was still kept at level 1 on the Torino impact hazard scale until August 2006. Then it broke the record for being at level 4. On August 5, 2006 Apophis was dropped from level 4 to level 0 on the Torino scale because new observations of Apophis showed that the keyhole would be missed. On October 19th 2006 the impact probability for April 13 2036 was calculated as 1 out of 45000 (2.22%). The 2037 date was also identified and the impact's probability was calculated to as 1 out of 12.3 million. [] []

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**//__Ezzatullah Rudi__//**
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