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It's a Bird, It's a Plane, It's... Oh No!

So where's Superman when you need him?

By Lavinia Ponniah

z2205007@student.unsw.edu.au

Since the Shoemaker-Levy comet collision with Jupiter in July 1994, there has been a rage of theories suggesting that the same devastating misfortune could happen here on Earth. In response, the National Aeronautics and Space Administration (NASA) has appointed a committee of scientists and astrophysicists to plot all near-earth objects (comets and asteroids) that may threaten Earth in the next 10 years.


The Shoemaker-Levy comet, now in pieces, on its way to impacting Jupiter.
(Shot from The Hubble Space Telescope)


Two thousand asteroids are estimated to exist with a diameter greater than 1 kilometer that are also due at some point to cross the orbit of Earth. This makes the possibility of a collision, although remote, still very real. Thankfully, these cosmic impacts only occur once every 200,000 years or so. Large comets also pose a threat. When these comets are pulled towards the Sun it breaks them up into a stream of debris. If these rather large particles of space dust gather around earth's atmosphere, it could cause another Ice Age. An actual collision with a comet's nucleus would also be cataclysmic.

[ Almost certainly, the dinosaurs of 65 million years took the brunt of something big and awful that fell from the sky. Dr. Frank Kyte, a geophysicist at the University of California at Los Angeles, recently (November 1998) published a paper in the journal Nature stating that he had found the very first physical evidence of this dino-killing asteroid. It was a small coarse-grained fleck containing tell tale ingredients of Iridium, and levels of iron, nickel, and chromium found only in outer space. The specimen was found on the floor of the Pacific Ocean at just the point where the Cretaceous period of massive dinosaurs transitions into the Tertiary epoch 65 million years ago. This transition layer is known as the K/T boundary. This highly distinctive layer marks, it is believed, the results of a gigantic amount of asteroid kicked-up debris that eventually settled back to earth after annihilating impact. -- Ed.]

These past few years, the consequences of such a large-scale impact disaster have been the focus of everything from religious cults to movie blockbusters. Between them, the concept of Armageddon has been exploited to its fullest. There is, however, a scientific basis for at least some of this hysteria. About 10 years ago, in 1989, a cosmic boulder, just slightly bigger than an aircraft carrier, passed within 400,000 miles of the Earth. This is a fairly close shave in astronomical terms.

However, most astronomers seem more concerned about the collision between Earth and the flying objects in the Taurid stream. The Taurid stream consists of cosmic rubble and dust. This space borne debris travels at a break neck speed of 46,000 mph and swings through the Earth's orbit on biannual crossings.

Dr. Victor Clube of the Department of Astrophysics at Oxford University has suggested that the 'megatonnage' explosion resulting from an impact with such celestial objects would produce an immense amount of debris. It could block out the sun for a considerable amount of time, throwing the world back into the Ice Age. But Dr. Clube and his fellow scientists are as concerned about the atomic solution suggestions in some "end of the world" movies, like "Deep Impact" and "Armageddon." Shattering incoming asteroids or comets with nuclear weapons could actually pose a greater danger to earth. Instead of one large threat, we will be faced with a massive amount of space debris that would still throw Earth into darkness on impact.



The Shoemaker-Levy comet impacting Jupiter.
Each small bright impact flash is bigger than planet Earth!


There is also an "atomic bullet" targeting problem. According to a paper published in Nature on June 4th, 1998, asteroids were mapped and found to be multi-lobed. Thus, they were not so much like a solid rock but more like a gravel pile loosely held together by fine dust. Therefore a single nuclear detonation could be totally absorbed by just one lobe of the object. Hence, an atomic explosion would likely not damage or deflect the asteroid as intended.

So how to defend ourselves? The first thing we have to do is find and precisely locate the biggest potential threats. The most recent development in asteroid and comet tracking has been achieved with the installation of new telescope pointing and control software called the Lowell Observatory Near-Earth Object System (LONEOS), installed at Lowell Observatory. LONEOS has now produced its first full set of detailed images. Preliminary performance results suggest that LONEOS would be able to survey about 10,000 square degrees of space each month.

The LONEOS telescope control program has been modified to accept pointing directions from its camera control computer. A program that generates macros for the camera control computer enables the telescope to take long sequence of images without observer intervention. Using LONEOS, scientists at the Lowell Observatory discovered the most recent Near-Earth object on 18 June 1998, called 1998MQ. At first the object didn't seem to be moving and was ignored. Later, they discovered that it had moved about 7 degrees north and appeared to be moving rather quickly. This led to much discussion, and not more than a little excitement in the media. Fortunately, it was a harmless event.

The fact is most asteroids and comets that are orbiting on an Earth-crossing course have not been discovered yet. Even with modern systems like LONEOS it will take more than a century to have mapped all of their locations. If Earth were to be on the receiving end of an asteroid or comet, we would have almost no warning whatsoever. The only indication that something really bad had just come our way would be a ground shattering explosion, supersonic shock wave and a blinding blast of light, all too late. These unsettling facts serve to underscore a recent suggestion by David Morrison, head of the Space Science Division at NASA Ames Research Center in Mountain View, California. Morrison is urging that the only way to successfully keep track of potentially dangerous asteroids is to install at least six of the $12 million LONEOS telescopes throughout North and South America. Until these additional systems are built, earth is flying almost blind.

But even assuming we had a globally dispersed system that provided earth with early impact detection and several months or more of warning what could we do about it? One possible answer comes from NASA. In collaboration with The Institute of Aeronautics and Astronautics (IAA), NASA is proposing to manufacture power units that could attach themselves to celestial boulders and divert these hazards away from Earth. One multi-million dollar effort researching the feasibility of asteroid deflection is Clementine 2. This project involves launching a satellite into a distant orbit that is equipped with high-speed probes that can locate and "lock on" to asteroids. The probes then proceed to strike the targeted objects at speeds of up to 40,000 mph. Each Clementine 2 probe has been designed to include sophisticated camera equipment to record the deflective effect on the approaching asteroid.

Another method much discussed in scientific circles is using lasers to deflect approaching asteroids. Asteroids and comets in space have devastatingly cold temperatures on their surfaces. The atmosphere in space and the speed at which the objects travel cause these extremely low temperatures. The idea is to use a laser beam large enough to heat the surface of an approaching asteroid. The heat created would then 'boil off' the asteroid. This is the same heating phenomenon the asteroid would go through if it were to penetrate our atmosphere at high speed. The thrust forces caused by escaping gases coming off the object's laser heated surface should be large enough to change the orbit of the asteroid, but only by a small amount. However, even a few degrees in course change may be enough to change its collision path with earth.

But there are a few disadvantages with this laser heating method. If the heated gases cause a deflection in the opposite direction as intended, that could turn a near miss into a definite impact! Furthermore, laser beams, while nominally parallel, may not be sufficiently so over tens of millions of miles. The great distances involved would cause laser beam spreading which in turn reduces heat concentration. Therefore, the only effective method for using lasers is at close proximity. In addition, accurate aiming also poses a problem. More problems arise when the laser beam has to target a moving object. The laser approach also needs about 10-15 years to work effectively because of the lack of concentration of the heat from the laser as it is transmitted over such a large distance in space. Therefore the asteroid that becomes the target needs to be spotted many years in advance And because the direction of thrusts from the expulsion of the gases from the asteroid's surface cannot be predicted (because the asteroid is not of uniform density and consists of lobes) it is also safer that the laser be used at larger distances to prevent a near miss from becoming a definite impact.

One proposed idea for better targeting is to use a laser beam source stationed in earth orbit that would work on objects which remained at a certain 'constant' distance from Earth. Even so, precautionary measures would need to be taken to ensure the path the laser takes while shooting at the moving asteroid does not cross the Earth's surface. Laser beams of such high power can cause severe damage to the very planet it is trying to protect.

American Professor Jay Melosh and Russian professor Ivan Nemchinov have also proposed launching a mirrored aluminum sail-like satellite into an orbit that tracks dangerous asteroids. Their idea is based on the boy scouts method of starting a fire using a magnifying glass to reflect and concentrate the Sun's rays. Similar to a laser's effect, the reflective disc collects Sun rays, raises them to approximately 2000 degrees in temperature, and focuses them onto a point on the asteroid, hence vaporizing ice and rock from it's surface. But Melosh and Nemchinov concede that, as with lasers, the lack of concentration of heat on the object's surface also means long range advance information of approximately 10-15 years is absolutely vital for their machine to work. It will take that long for the sun's rays to do their job.

Another idea to deflect earth-bent asteroids was developed by the Space Studies Institute (SSI). They took the idea of the Clementine 2 power units developed by NASA and IAA, and made a slight, but very significant modification. Instead of a kamikaze probe that locked on and attacked the asteroid at high speeds, SSI's probe would gently land on the asteroid, and then firmly attach itself. The probe's mass driver engine would then produce the low, yet steady and continuous thrust needed to gradually change the asteroid's course, using the asteroid's own material for reaction mass.

The SSI design also heralds a new era when earth is no longer threatened with extinction by asteroids, but instead benefits from them. The SSI mass driver engine is also designed for drilling and mining on asteroids. Once the dangerous object was shepherded into a High Earth Orbit and rendered safe, mining on the asteroid would be carried out. This project holds the promise of obtaining vast amounts of raw materials and resources in a manner not damaging to our environment.

But until that benign asteroid day, heads up!


Copyright 1998, Lavinia Ponniah, All Rights Reserved

 

21st, The VXM Network, http://www.vxm.com

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