NASA had estimated that an impact from Apophis, which has an outside chance of hitting the Earth in 2036, would have released more than 100,000 times the energy released in the nuclear blast over Hiroshima. Thousands of square kilometers would be directly affected by the blast but the whole of the Earth would see the effects of the dust released into the atmosphere.
As Monica Grady, an expert in meteorites at the Open University, said:
"It's a question of when, not if, a near Earth object collides with Earth. Many of the smaller objects break up when they reach the Earth's atmosphere and have no impact. However, a NEO larger than 1km [wide] will collide with Earth every few hundred thousand years and a NEO larger than 6km, which could cause mass extinction, will collide with Earth every hundred million years. We are overdue for a big one."
Apophis had been intermittently tracked since its discovery in June 2004 but in December 2005, it began to cause serious concern As of this time, the chances of Apophis hitting Earth has been reduced to 1 in 12.3 million.
In projecting the likely orbit of the Apophis into the future, astronomers calculated that the odds of it hitting the Earth in 2029 were alarming and the odds got higher as more observations were received. At the peak of the scientists' concern, Apophis asteroid was placed at 4 out of 10 on the Torino scale - a measure of the threat posed by an NEO where 10 is a certain collision which could cause a global catastrophe. This was the highest of any asteroid in recorded history and it had a 1 in 37 chance of hitting the Earth. The threat of a collision in 2029 was eventually ruled out at the end of 2004 and the collision date extended to approximately 2036. The Torino scale threat has also been lowered to 0 out of 10.
Alan Fitzsimmons, an astronomer from Queen's University Belfast, has stated that the asteroid should pass close to earth on April 13th 2029 and when it does:
the Earth will deflect it and change its orbit. There's a small possibility that if it passes through a particular point in space, the so-called keyhole, the Earth's gravity will change things so that when it comes back around again in 2036, it will collide with us."
The chance of Apophis passing through the keyhole, a 600-metre patch of space, was 1 in 5,500 based on information in 2005 but as of the most recent information, it is now 1 in 45,000.
The Advanced Concepts Team at the European Space Agency have led the effort in designing a range of satellites and rockets to nudge asteroids on a collision course to Earth into a different orbit. Even nuclear powered spacecraft are being considered but the negative aspect of nuclear powered is that it has not yet been put to the test as is the case with solar electric propulsion, for which there are already several spacecraft that do use the latter technology.
The European Space Agency (ESA) favoured method is also one of the easiest methods - to throw a spacecraft at an asteroid to change its direction. ESA plans to test the idea with its Don Quixote mission, where two satellites will be sent to an asteroid. One of the spacecraft, Hidalgo, will collide with the asteroid at high speed while the other, Sancho, will measure the change in the object's orbit. Decisions on the actual design of these probes were to be made in 2006, with an expected launch to take place sometime between 2007 and 2017 launch expected some time in the next decade. Astronomers are not considering the use of explosives as an option due to the fact of potential spread of damage by the collision of many fragments.
In September 2005, scientists at Strathclyde and Glasgow universities began computer simulations to work out the feasibility of changing the directions of asteroids on a collision course for Earth.
POSSIBLE EFFECTS OF IMPACT
NASA initially estimated the energy that Apophis would have released if it struck Earth as the equivalent of 1480 megatons of TNT but later refined this to 880 megatons. The impacts which created the Barringer Crater of the Tunguska event are estimated to be in the 10-20 megaton range and the 1883 eruption of Krakatoa was the equivalent of roughly 200 megatons.
The exact effects of any impact of an asteroid varies according to the asteroid's composition, and its the location and angle of impact. Any impact is aid to be extremely detrimental to an area of thousands of square kilometres, but information says that any impact would probably not cause long-lasting global effects, such as the initiation of an impact winter as many fear.
Origin: fromatlantistosphinx.blogspot.com
