The world we live in was never hundred per cent safe. And the hazards that stare life in the face are numberless. So, it is a very hostile world in which life survives. But for a human, the most intelligent form of life, at least here on earth, the hazards, especially those due to natural causes, have a quite different connotation from other forms of intelligent life. It is their knowledge that makes them different from others.
They know what is threatening them now and they can also foresee what may come in the future. So, it is their knowledge that causes them to suffer more than other animals. But though ignorance is bliss, knowledge has also its redeeming features. They can take advance preparations to ward off future hazards.
A potentially dangerous object orbiting round the sun is an asteroid called Apophis, named after the mythical Egyptian spirit of death, is on a collision course with the earth and may strike us within a span of two or two and a half decades.
Now, what are asteroids? They are space debris in the form of rocks of different sizes orbiting the sun. There are many hypotheses about the origin of asteroids. Some say those are the pieces of a planet destroyed by an unknown natural cause in the remote past lost in the mist of time. Other theories are of the view that asteroids are materials, mostly gaseous and probably thrown off by the sun when planets came into existence. The exception was that they never made a planet, because they were too small to make one. They are also called minor planets. Talking about size, they range from the very big ones as large as Ceres, which is about 1,000 km across, to the very small ones, the size of pebbles. Sixteen asteroids have a diameter of 240 km or greater. They have been found inside Earth's orbit to beyond Saturn's orbit. Most, however, are contained within a main belt that exists between the orbits of Mars and Jupiter. Some have orbits that cross Earth's path and some have even hit the Earth in times past.
In fact, if the estimated total mass of all asteroids was gathered into a single object, the object would be less than 1,500 kilometres (932 miles) across -- less than half the diameter of our Moon.
Much of our understanding about asteroids comes from examining pieces of space debris that fall to the surface of Earth. Asteroids that are on a collision course with Earth are called meteoroids. So, Apophis, about which we are concerned here, is also a meteoroid. When a meteoroid strikes our atmosphere at high velocity, friction causes this chunk of space matter to incinerate in a streak of light known as a meteor. If the meteoroid does not burn up completely, what's left strikes Earth's surface and is called a meteorite. But since Aphophis is a fairly large meteoroid, it has no chance of burning up as a result of its collision with the atmosphere.
Of all the meteorites examined, 92.8 percent are composed of silicate (stone), and 5.7 per cent are composed of iron and nickel; the rest are a mixture of the three materials. Stony meteorites are the hardest to identify since they look very much like terrestrial rocks.
Because asteroids are material from the very early solar system, scientists are interested in their composition. Spacecraft that have flown through the asteroid belt have found that the belt is really quite empty and that asteroids are separated by very large distances.
Returning to the behaviour of Apophis, let us see what the scientists are prognosticating about its behaviour, especially its chance of hitting the earth in not-so-distant future, as reported by Alok Jha, the science correspondent of the popular British newspaper, The Guardian.
In ancient Egypt, there was a mythical evil demon called Apophis, who was bent on engulfing the earth into the abyss of darkness. And endless, perpetual darkness means death to life.
"A fitting name, astronomers reasoned, for a menace now hurtling towards Earth from outer space. Scientists are monitoring the progress of a 390-metre wide asteroid discovered last year that is potentially on a collision course with the planet, and are imploring governments to decide on a strategy for dealing with it.
Nasa has estimated that an impact from Apophis, which has an outside chance of hitting the Earth in 2036, would release more than 100,000 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.
And, scientists insist, there is actually very little time left to decide. At a recent meeting of experts in near-Earth objects (NEOs) in London, scientists said it could take decades to design, test and build the required technology to deflect the asteroid. 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 last year but, in December, it started causing serious concern. Projecting the orbit of the asteroid into the future, astronomers had calculated that the odds of it hitting the Earth in 2029 were alarming. As more observations came in, the odds got higher.
Having more than 20 years warning of potential impact might seem plenty of time. But, at last week's meeting, Andrea Carusi, president of the Spaceguard Foundation, said that the time for governments to make decisions on what to do was now, to give scientists time to prepare mitigation missions. At the peak of concern, Apophis asteroid was placed at four 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 last year.
Alan Fitzsimmons, an astronomer from Queen's University Belfast, said: "When it does pass close to us on April 13 2029, 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, is 1 in 5,500 based on current information.
There are no shortage of ideas on how to deflect asteroids. 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 for Earth into a different orbit.
No technology has been left unconsidered, even potentially dangerous ideas such as nuclear powered spacecraft. "The advantage of nuclear propulsion is a lot of power," said Prof Fitzsimmons. "The negative thing is that ... we haven't done it yet. Whereas with solar electric propulsion, there are several spacecraft now that do use this technology so we're fairly confident it would work."
The favoured method is also potentially the easiest - throwing a spacecraft at an asteroid to change its direction. Esa plans to test this idea with its Don Quixote mission, where two satellites will be sent to an asteroid. One of them, 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 will be made in the coming months, with launch expected some time in the next decade. One idea that seems to have no support from astronomers is the use of explosives.
Prof Fitzsimmons. "If you explode too close to impact, perhaps you'll get hit by several fragments rather than one, so you spread out the area of damage."
In September, 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. In spring next year, there will be another opportunity for radar observations of Apophis that will help astronomers work out possible future orbits of the asteroid more accurately.
If, at that stage, they cannot rule out an impact with Earth in 2036, the next chance to make better observations will not be until 2013. Nasa has argued that a final decision on what to do about Apophis will have to be made at that stage.
"It may be a decision in 2013 whether or not to go ahead with a full-blown mitigation mission, but we need to start planning it before 2013," said Prof Fitzsimmons. In 2029, astronomers will know for sure if Apophis will pose a threat in 2036. If the worst-case scenarios turn out to be true and the Earth is not prepared, it will be too late. "If we wait until 2029, it would seem unlikely that you'd be able to do anything about 2036," said Mr Yates."
This is undoubtedly a doomsday scenario, narrated in no-nonsense terms. It is hard science that is predicting such a possibility of cataclysm in the near future. It is undoubtedly a frightening narrative. The meteoroid of Tunguska in Siberia destroyed only a large swathe of the forestland and the animals living there. But had the meteor crashed into a populated place, the scale of destruction would be quite beyond imagination. It is said that the era of dinosaurs ended after a meteoroid of a far larger size crashed into the earth. With the power of science and knowledge in hand, we are surely better equipped than the dinosaurs not to yield to the dark forces of nature. Who knows what the future has in store for us!
