Thursday, November 5, 2009

Armageddon on unlucky Friday 13th

In 1998 a science fiction film, Armageddon, starring Bruce Willis was released. The movie was about a group of blue-collar deep-core drillers who are sent by NASA to deflect an asteroid on a collision course with Earth. At the time the movie attracted only Bruce Willis fans but now scientists all over the world are renting and watching this movie along with scores of other sci-fi movies to see if they can really find a way to escape doomsday – a giant asteroid hurtling towards Earth.

Even though it is not common knowledge, the truth is that 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. 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.

In 1994, something happened which showed us how imminent the danger is. Astronomers realised that comet Shoemaker-Levy 9 was heading straight for the planet Jupiter. The stunning - and violent - impact created an explosion the size of planet Earth, and it was the first time a collision between two astronomical bodies had been observed. If Jupiter had been hit, then the Earth could be next. And it seems the scientists’ worst fears were coming true.

In 2004 an asteroid was discovered and estimated to be directly on collision course with Earth. Scientists named it Apophis. Apophis's length was estimated to be 350 m (1150 ft).Upon its discovery in 2004, Apophis was briefly estimated to have a 2.7% chance of impacting the Earth in 2029. However, there will be a historically close approach to the Earth, estimated to be a 1 in 800 year event (on average, for an object of that size).

On Friday, April 13, 2029 Apophis will approach the Earth no lesser than 29,470 km (18,300 miles, or 5.6 Earth radii from the center, or 4.6 Earth-radii from the surface) over the mid-Atlantic, probably appearing to the naked eye as a moderately bright point of light moving rapidly across the sky. Depending on its mechanical nature, it could experience shape or spin-state alteration due to tidal forces caused by Earth's gravity field.

Even then another danger faced is the threat of collision with artificial satellites. However the European Space Agency has dismissed such threats. According to them (1) Apophis does not pass near the zones where most satellites are located and (2) man-made satellites and Apophis both have small cross-sectional areas. Even if a high-velocity impact occurred, at most a large satellite could change Apophis' position 7 years later (in 2036) by only 100's of km. This can have no meaningful effect on Earth impact probability estimation. At such a late date, impact with an artificial satellite would be like a bug on the windshield of Apophis.

Wait before you breathe with relief. New studies have shown that there is 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 600 meters across, which would set up a future impact in 2036 on – guess when – again April 13th !!

The exact effects of any impact would vary based on the asteroid's composition, and the location and angle of impact. Any impact would be extremely detrimental to an area of thousands of square kilometers, but would be unlikely to have long-lasting global effects, such as the initiation of an impact winter.

An impact winter is a period of prolonged cold weather caused by the impact on the Earth of a large asteroid or comet. If such an impact occurred on land or the floor of a shallow sea, it could cause large amounts of dust or ash to be thrown into the Earth's atmosphere, blocking the Sun's light and dramatically lowering the amount of sunlight reaching the earth's surface. Impact winter is one of the mechanisms proposed for Extinction Level Events (ELE), such as the asteroid impact at Chicxulub in Mexico which supposedly led to the extinction of the dinosaurs.

So how do you face this threat to humanity? Will the method in the movie of using nuclear weapons work?

The most obvious strategy to protect the Earth against an asteroid might seem to be to try to destroy it with nuclear weapons. This plan has two fundamental problems. Firstly, you would have to attach a bomb larger than any yet created, to a very powerful rocket. This might be nearly as dangerous as the asteroid you were trying to destroy.

More importantly however, a nuclear blast might not destroy a large asteroid completely, but merely split it into chunks. Instead of one large impact, you might end up with several smaller ones, which would end up doing nearly as much damage.

If we cannot destroy an approaching asteroid, then the only other tactic would be to try to nudge it forward just enough to make it miss the Earth - like stepping on the accelerator of a car to make it miss a train at a level crossing.

Some scientists think they can use the power of the Sun to nudge an asteroid away from the Earth. After all the sun is the biggest power source in the Solar System. In the same way as you can use a magnifying glass to set fire to a sheet of paper, you could focus the Sun's rays onto a point on the surface on an asteroid. The spot where the Sun's rays met would heat up, blasting particles of the asteroid into space. This would act like a rocket engine, and might be enough nudge the asteroid out of harm's way.

Hopefully our scientists will also devise something to hold these threats at bay or we could soon be following the dinosaurs.


Apophis is the Greek name of the Ancient Egyptian enemy of Ra: Apep, the Uncreator, a serpent that dwells in the eternal darkness of the Duat (underworld) and tries to swallow Ra during His nightly passage. Apep is held at bay by Set, the Ancient Egyptian god of Chaos.