The Earth is under constant bombardment. Each year, many fragments of debris hit our planet. Fortunately for us, most are so small that they burn up harmlessly in the atmosphere.
However, there are hundreds of larger asteroids orbiting near the Earth. Many scientists now believe that one of these hit the Earth 65 million years ago, killing the dinosaurs, along with 90% of all life on the planet. What is more, it is only a matter of time before the Earth is hit again.
Apophis – previously known by its provisional designation 2004 MN4 – is a Near-Earth asteroid that caused a brief period of concern in December 2004 because initial observations indicated a relatively large probability that it would strike the Earth in 2029. Additional observations provided improved predictions that eliminated the possibility of an impact on Earth or the Moon in 2029. However there remained a possibility that during the 2029 close encounter with Earth, Apophis would pass through a "gravitational keyhole", a precise region in space no more than about 400 meters across, that would set up a future impact on April 13, 2036. This possibility kept the asteroid at Level 1 on the Torino impact hazard scale until August 2006.
Additional observations of the trajectory of Apophis revealed the "keyhole" would likely be missed and on August 5, 2006, Apophis was lowered to a Level 0 on the Torino Scale – a method for categorizing the impact hazard associated with Near Earth Objects. As of October 19, 2006 the impact probability for April 13, 2036 is estimated at 1 in 45,000.
Basic data...
It was discovered on June 19, 2004, by Roy A. Tucker, David J. Tholen, and Fabrizio Bernardi of the NASA from Kitt Peak National Observatory.
When first discovered, the object received the provisional designation 2004 MN4, and news and scientific articles about it referred to it by that name. When its orbit was sufficiently well calculated it received the permanent number 99942, the first numbered asteroid with Earth-impact solutions. Receiving a permanent number made it eligible for naming, and it promptly received the name "Apophis" as of July 19, 2005. Apophis is the Greek name of the Ancient Egyptian god Apep, "the Destroyer", who dwells in the eternal darkness of the Duat (underworld) and tries to destroy the Sun during its nightly passage.
Close approaches...
After the Minor Planet Center confirmed the June discovery of Apophis, the next close approach was computed to be April 13, 2029. On that date, it will become as bright as magnitude 3.3 (visible to the naked eye from rural and some darker suburban areas, visible with binoculars from most locations). It is important to note that the close approach in 2029 will substantially alter the object's orbit, making predictions uncertain without more data.
Since the odds of impact are known to be very low, the possible effects of an impact are largely irrelevant. However, the initial reports resulted in widespread discussion on many Internet forums, including armchair speculation about exactly where Apophis (then known only as 2004 MN4) would hit and what would happen when it did.
NASA estimated the energy that Apophis would have released if it struck Earth as the equivalent of 400 megatons of TNT. The impacts which created the Barringer Crater or caused the Tunguska event are estimated to be in the 10-20 megaton range. The 1883 eruption of Krakatoa was the equivalent of roughly 200 megatons.
The exact effects of any impact would have varied based on the asteroid's composition, and the location and angle of impact. Any impact would have been extremely detrimental to an area of thousands of square kilometres, but would have been unlikely to have long-lasting global effects, such as the initiation of an impact winter.
The astroid Apophis was a close call and also was an eye-operner for all the scientists around the world to be ready for any future hazards of astroids or comet impacts.
Thilina Heenatigala
General Secretary
Sri Lanka Astronomical Association
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