What if an asteroid hits the earth?

By Syed Akbar
Hyderabad: Astronauts from around the world are discussing and chalking out a strategy on
earth-threatening asteroids, some of which may collide with the human planet in the next few decades leaving a trail of death and destruction.
They are also discussing a range of possible options for deflecting a threatening object and outline opportunities for future research on the nature of asteroids and comets.
The 2036 close approach of the asteroid Apohis, which is currently predicted to have a one in 45,000 change of impacting the earth, will be highlighted at the conference as an example. During its close passage by the Earth on April 13, 2029, it is possible that asteroid Apophis will pass through a
keyhole leading to a collision in 2036.
According to an estimation by the National Aeronautics and Space Administration, an impact from Apophis would release more than one lakh times the energy released in the nuclear blast over Hiroshima.
"Thousands of square kilometres would be directly affected by the blast
but the whole of the earth would see the effects of the dust released into the atmosphere," NASA scientists points out.
NASA has suggested two possible methods of protecting the earth from an
asteroid or comet determined to be on a collision course, by destroying the object before it hits the earth or by deflecting the object from its orbit before it hits the earth.
To destroy the earth-approaching object, astronauts would land a spacecraft on the surface of the object and use drills to bury nuclear bombs deep below its surface. Once the astronauts were a safe distance away, the bomb would be detonated, blowing the object to pieces. Drawbacks to this approach
include the difficulty and danger of the mission itself, and the fact that many of the resulting asteroid fragments
might still hit the Earth, resulting in massive damage and loss of life.
In the deflection approach, powerful nuclear bombs would be exploded up to half a mile away from the object. The radiation created by the blast would cause a thin layer of object on the side nearest the explosion to vaporise and fly into space. The force of this material blasting into space would recoil
the object in the opposite direction just enough to alter its orbit, causing it to miss the earth.
NASA now supports, in collaboration with the United States Air Force,  the Spaceguard Survey and its goal of discovering and tracking 90 per cent of the Near Earth Asteroids with a diameter greater than about one kilometre by next year.