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article imageOp-Ed: Asteroid 2005 YU55 a harbinger of future catastrophe?

By JohnThomas Didymus     Nov 7, 2011 in Science
Tomorrow's close approach of an asteroid 400 meters across sends, once again, the message to us that we live in an environment in which the threat to our survival comes not only from our activities on Earth but from events in space outside our control.
When we discuss the problem of human survival on Earth, we think mostly about the impact of our activities on the environment and also of the threat of nuclear weapons. Yet the evidence coming to light in recent times is that catastrophic impacts of astro-bodies with the Earth over the geological ages have played a greater role in evolutionary history than we had previously suspected. It is now widely accepted that the planet-wide extinction of dinosaurs about 65 million years ago was the result of a meteor impact with global catastrophic consequences.
A few astronomers have argued that objects of greatest risk to us in the short term are not space objects (meteorites and asteroids) over 1,000 meters whose approach may be detected by the Spaceguard survey, but smaller objects a few meters to hundreds of meters across. The impact rate of space objects in the class 5 to 10 meters is uncomfortably high, and the potential consequences in the event of such impact occurring close to human population center could be devastating.
Space rocks in the 5-10 meter range impact on the earth almost every year with as much explosive energy as the Hiroshima atom bomb (a 15 kiloton weapon). Most, however, impact only in the upper atmosphere where most of the solid constituent vaporize. Astronomers estimate objects in the 50 meters range impact on the Earth about once every thousand years and produce explosions equal to 10 megatons of TNT (several times the Hiroshima bomb). We know one such impact occurred in Siberia on June 30, 1908, and flattened more than a thousand square kilometers of forest. But, fortunately, the Siberia region is a desolate region. Had the explosion occurred over a city, the death toll would have been catastrophic.
Astronomers say if we were to sustain direct impact with an asteroid the size of 2005 YU55 expected to zip past the Earth tomorrow, we would experience a massive explosion equivalent to that set off by more than 50 megaton nuclear weapon. Such an explosion would cause widespread destruction covering several thousands square kilometers. The impact will excavate a crater 4 miles wide and cause an earthquake of magnitude 7 on the Richter scale.
The impact rate estimate of one per thousand years for space objects in the size range believed to have caused the Siberian explosion is just too high for comfort. Going by current estimates of impacts involving space rocks in the 10-50 meters range, one is almost certain to impact in this century. Impacts involving objects of about 30 meters are estimated as occurring every few years. The only hope we have of averting a nuclear bomb scale catastrophe in the not-too-distant future is that we develop technology to prevent it.
God Discussion details some of the close brushes we have had in recent times:
On August 10, 1972, a meteor literally grazed the Earth passing within 57 kilometers. It was seen by many people moving north over the Rocky Mountains to Canada, and was estimated to be about 8 meters in diameter. A slightly larger meteor entering the Earth's atmosphere at an angle of 45 degrees could have caused as much as a 5 kiloton blast at sufficiently low altitude to cause casualties.
On March 23, 1998, a 300-meter Apollo asteroid missed the Earth by 6 hours(that is, it passed the point where the Earth had been six hours before), Had the asteroid impacted, it would have created a massive explosion, the largest in human history: a thousand times more powerful the largest nuclear bomb ever exploded. What is most unnerving about this incident is that scientists were unable to calculate, with precision, how close it would pass to the Earth. We did not know whether or not it would impact on the Earth until after it had actually missed.
On June 6, 2002, an object with an estimated diameter of 10 meters collided with the Earth over the Mediterranean Sea between Greece and Libya. The object exploded in mid-air releasing energy equivalent to 26 kilotons of TNT, more than one and a half times a Hiroshima class bomb.
On March 18 2004, the closest to a catastrophic impact occurred when a 30 meter asteroid missed the earth by only 42,600 kilometers(only about one-tenth the distance of the earth to the moon!) It was later estimated by scientists that such near miss occur once every two years. Note that a 30 meter asteroid impacting on the earth would have caused an explosion several times the Hiroshima bomb class of nuclear device, causing catastrophic devastation to human populations, if the impact were over, or in the vicinity of a large city.
The evidence is that chances of a disastrous meteor or asteroid collision with the Earth are high enough for us to be concerned with developing technologies for deflecting such bodies. quotes former astronaut Rusty Schweickart, Chairman of the B612 Foundation, a group that is working to prevent deadly meteorite or asteroid impact with the Earth:
"We have the capability — physically, technically — to protect the Earth from asteroid impacts...We are now able to very slightly and subtly reshape the solar system in order to enhance human survival."
What are the options available to us? lists some of them:
We could use the gravity tractor method, that is, a spacecraft's gravity could be used to exert a deflecting tug on an asteroid as the spacecraft passes close to it. We could crash a robotic probe into the space body and deflect the body from a path threatening the Earth (this method is considered less precise than the gravity tug method). reports that recently, NASA crashed an impactor on comet Tempel 1, in the attempt to determine its composition.
The final most radical alternative is to blow the asteroid to pieces with a nuclear device. The danger is that this could turn a single body on collision course with the Earth into a deadly shower of several bodies with potential to cause even more widespread destruction than the intact body.
Yet another more technically challenging but feasible option is the "mirror bee" technique in which it is proposed to launch several small spacecrafts carrying mirrors which would direct light reflected from the Sun on the Earth-menacing space rock, heating it up till it vaporizes., however, points out that while all these options are viable, the biggest challenge would be detecting the threat in time to mobilize for effective action.
The sobering truth is that our Spaceguard survey is still in infancy. Objects in the size class of a few tens to a few hundreds of meters across could easily pass undetected and wreak havoc on a local population or even an entire region. The chances are that by the time we detect a body of say 30-50 meters across that could set off an devastating explosion of up to 10 megatons of TNT, it would be too late for us to mobilize to prevent it.
This opinion article was written by an independent writer. The opinions and views expressed herein are those of the author and are not necessarily intended to reflect those of
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