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MN 4

It is the storyline of a disaster movie that we have all watched and said, “Great film but it can never happen, it’s too far fetched” The plot is an asteroid is on a collision course with the Earth and if its hits the planet all life will cease. Of course in the movie we always have a few nuclear missiles available and a major power willing to throw everything at the malevolent asteroid to destroy it before it arrives. The major power usually turns out to be the USA who has at least one tame scientist predicting the end of the world if we do not do something about it and the solution employed will only have a one in a million change of success. It makes for a fine cliffhanger of a disaster movie but it could never happen “Right”……..Wrong.

In the vast expanse of space and on its way to a locality near you at this very moment is an asteroid called Apophis. It was discovered in June 2004 and was given the scientific designation of “2004 MN4”. It is thought to be around the size of Wembley Stadium [415 metres across] and is currently moving at a velocity of 30.75 km/sec. Its orbit of our Sun takes 323 days where the Earth orbit of the same body is 365/366 days. The orbital paths of Apophis and the Earth are elliptical, the Earth orbit is broadly speaking uniform but Apophis is not. It is merely a question of time before both objects find themselves trying to occupy the same space at the same time E.G. collision.
Discounting “Devine” intervention or the possibility of Apophis accidentally colliding with a passing meteor or comet we can expect the first encounter with Earth to take place in 2029 and assuming both the Earth and Apophis both survive the encounter there will be a second encounter in 2036. It was originally calculated that the asteroid would come no nearer than 187,000 miles of the Earth but that “Safety margin” was thought optimistic and recalculations put the asteroid on its first earth encounter inside the orbital path of our Moon. The new prediction of how close MN4 will come to the surface of the Earth puts its path at one tenth of the distance between the Earth and the Moon [approximately 9,000 miles].

The equatorial surface gravity of Apophis is unknown as is its mean density but such an object passing in close proximity to the Earth is certain to affect tidal oceans, the magnetic core of the Earth, the tectonic plate structure and volcanic activity even if no fragments of Apophis manage to penetrate the Earth atmosphere. 2029 is almost certain to be a year when earthquakes, volcanoes, extreme weather and natural disasters manifest in increasing numbers.

That a piece of rock is hurtling toward the Earth at better than 30 Km/sec is now undeniable, its exact path/trajectory is still under discussion and there is still a great deal that needs to be clarified about the exact nature of the beast but it is almost certain that the one thing that will not be done is to destroy the asteroid with explosive devices nuclear or otherwise.

Whilst the asteroid presents a clear and present danger to the Earth, some solutions would exacerbate the situation and cause almost as much catastrophe than if we had done nothing. Attacking the asteroid with nuclear explosives may result in its fragmentation, the fragmentation will not be uniform some pieces would be larger than others and whilst the smaller fragments would burn up in our upper atmosphere the larger pieces would not. Some of those larger pieces could be fifty tons or more and their impact on the Earth surface could trigger earthquakes, initiate Tsunami’s cause vast forest fires or decimate cities containing millions of people.
In 1908 a large fragment of an asteroid did enter the Earth’s atmosphere but it did not complete its decent to the surface intact, it exploded above the Earth in an “Airburst” that flattened 2000 square kilometres of Siberian forest, there was little known loss of life but the implications of such a hit on present day Europe, USA or Asia would almost certainly kill millions of people. The asteroid in question was estimated to have been sixty metres in diameter; Apophis is nearly seven times bigger.

A less dramatic solution but far more effective way would be “Deflection” It would not destroy the asteroid but would alter its trajectory away from the Earth. There would be no dramatic last minute explosion just in time to save the planet but a carefully controlled impact/influence upon the body to alter its course.

There are two possible ways to deflect the object and both have merit. One solution is to affix a rocket or series of rocket engines to the asteroid and steer it away in the same way that bow thrusters steer ocean liners in confined harbours. It is an expensive solution but has the advantage of precision and is possibly reusable.

The second option is a little more dramatic but would still leave the asteroid intact and deflect it. In the same way as the balls on a pool/snooker table are hit with the cue ball to move them at an angle to their original position it is possible to simply “hit” the object with something heavy and deflect it on to a new course.
Not that long ago a mission left Earth to do something very similar. The site for the experiment was the far side of Jupiter from the Earth and the target was a comet.
The European space agency and NASA launched a rocket designed to attain speeds in excess of 25,000 mph carrying an 800lb lump of copper, using the immense gravitation of Jupiter it was accelerated up to 33,000 mph as the comet passed behind Jupiter the payload smashed into the comet, the result was penetration and a discernable deflection. The year was 2004,the mission was called “Deep impact” and it was successful.
The experiment was one of a series that would formulate a plan to deflect NEO’s [Near Earth Objects] away from the Earth. The data stream collected at the time was relayed back to Earth via a command vehicle that recorded the event, the command vehicle is still out there and its name was Sancho. Sancho was squire to Don Quixote who watched as his mentor tilted at windmills.


Posted: September 6, 2007 

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