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	Asteroids Picture showing asteroid Gaspra's Best Face An asteroid, also known as a minor planet or planetoid is a class of astronomical objects. It is a term generally used to indicate a small diverse group of celestial bodies that drift in the solar system around the Sun. Hundreds and thousands of asteroids have been found in our solar system and there is a present discovery rate of about 5000 per month. One asteroid I would particularly like to discuss as it generated a brief period of concern in December 2004 is 99942 Apophis. The reason for this concern as because initial observations indicated a large probability that it may strike Earth in 2029. Picture showing trees felled by the Tunguska blast On June 15 1908, 7:15am an object half the size of a football field headed towards our planet from space at 340,000 miles per hour producing a stream of fiery gas behind it. Within minutes it had entered our atmosphere and had become almost fireball at this stage. It violently exploded above Siberia's Tunguska forest. The energy of the blast was later estimated to be between 10 and 20 megatons of TNT, 1000 times more powerful than the bomb that dropped on Hiroshima or equivalent to Castle Bravo, the most powerful nuclear bomb ever detonated by the US. It felled an estimated 80 million trees over 2150 square kilometres. It measured 5.0 on the Richter Scale. Fortunately no one died directly from the explosion as it occurred over a thinly populated region. Imagine a recreation of such an event in today's time, it would potentially devastate a large metropolitan area thus crippling the socio-economical structure of a nation. Let's assume that it the meteorite entered our atmosphere a few hours later back in 1908. Then it would have struck Europe, and if it had exploded over midair, a million people would have possibly died. Below is a quote from a Siberian newspaper describing the explosions: "When the meteorite fell, strong tremors in the ground were observed, and near the Lovat village of the Kansk uezd two strong explosions were heard, as if from large-calibre artillery." There wasn't much scientific curiosity about the event at the time possibly due to the isolation of the Tunguska region. Nowadays it is believed that the leading explanation of the explosion is the airburst of a meteoroid 6 to 10 kilometres above the Earth's surface. With the situation regarding Apophis, we face a similar dilemma. There is a possibility that during the 2029 close encounter with Earth, Apophis could pass through a "gravitational keyhole", a precise region in space no more than about 400 meters across that would set up future impact on April 13, 2036. The gravitational effect of the earth would change Apophis' trajectory.. However as of October 19, 2006 the impact probability is estimated at about 1 in 45,000. Today we have the technology to stop near earth objects (NEO's) from impact, and can begin to reshape our local solar system. Because the chance of collision is low, the result of impact hasn't really been considered. However depending on the location and angle of impact, the product could be a detrimental effect to an area of thousands of square kilometres and initiate a nuclear winter. Videos Video showing Apophis investigation

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