ASTEROID NEARLY SMACKS EARTH - WHERE IS BRUCE WILLIS WHEN WE NEED HIM?
A rather large bullet skimmed our planet exactly one week ago. Had it hit, it would not have killed us, but could have dealt a painful flesh wound. Last Friday, June 14th, an asteroid passed unnervingly close to earth, well within the moon�s orbit. The asteroid was the largest that we have ever discovered to have crossed within the lunar orbit, and it also came much nearer than previous near-misses by large rocks. The asteroid measures between 150 � 300 feet in diameter, making it roughly the size of a soccer or football field (if such things were three-dimensional, unevenly surfaced, and composed of ferrous metals). Moving at a speed relative to the earth of over 6 miles per second, the asteroid passed just 75,000 miles away, fully a third less than the moon�s distance of 240,000 odd miles. In astronomical terms, that is a hair�s breadth. An asteroid of this size at this close range has never before been detected. It has been named and catalogued as 2002MN. The discovery was made and announced by New Mexico�s Lincoln Laboratory Near Earth Asteroid Research (LINEAR) search effort.
There are a number of aspects to this asteroid and its passage that are alarming, not least of which are the rock�s size, proximity, and velocity. Consider that the asteroid was not discovered until June 17th, a full 3 days after it made its unauthorized flyby. This is due to 2002MN�s trajectory, which was literally coming at us out of the sun, like the Red Baron barreling down on a kill. Imagine a more or less straight line from the sun to the earth, and that�s the path the asteroid was on. Due to this, it was almost impossible to have been spotted, even if we had been looking for it, because the asteroid would not have been visible to conventional nightside telescopes. As with staring at a spotlight, you can�t see if the people behind the spotlight are chucking dirtclods at you. Moreover, one can�t help but be alarmed by the potential responses of the various military forces of the world to an unexplained, sudden explosion of this magnitude. An asteroid the size and speed of 2002MN, if indeed not a comet but a rock composed of a relatively sturdy nickel-iron core, would have the destructive effect of a moderately sized nuclear weapon if it were to strike on land. In today�s political climate, it is not difficult to imagine the types of unfortunate events that could transpire in the wake of a completely unexpected, bolt from the blue such as this would be.
Asteroids are not harmless ships that pass in the night. Jupiter and Saturn, the large outer planets with their strong gravity, perturb the orbits of individual asteroids within the asteroid belt and send them on eccentric orbits around the sun independent of the majority of asteroids that reside within the steady orbit of the belt. As well, to a lesser extent the even more distant planets Uranus and Saturn, and even passing nearby stars, can send on sunward trajectories comets from the Oort Cloud and the Kuiper Belt, which are extremely distant comet-holding entities on the fringe of the sun�s gravitational influence. Most of these comets and asteroids will never run into the earth, but the laws of probability dictate that every so often, one will. The way in which the geologic record confirms this fact is almost eerie in its statistical precision. And it shows that relatively small impactors, such as whatever is likely to have caused Siberia�s Tunguska event in 1908, happen about once every century. That event obliterated everything on the ground within a 2,100 square kilometer area, below what looks to have been a cometary airburst. It was sheer luck that it occurred in unpopulated territory. Of course, given the distribution of water on our planet, the odds are in our favor that an asteroid such as last Friday�s 2002MN would not hit land, and even if did strike on a continent it is highly improbable that it would strike a bullseye in a major metropolitan center. That, however, is no reason not to take precautions. In a skewed analogy, we can imagine the earth as a car driving around a closed circular track. Once per lap, the car must drive under a bridge from which no-good teenage punks, Jupiter and Saturn, occasionally hurl stones at us. It would not hurt to drive defensively.
current science news posted by ted at 6/21/2002 01:49:00 AM
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