The ultimate environmental catastrophe, the threat from other space
There are tens of millions of asteroids in the solar system, and several thousand moves in orbits that take them close to Earth. Sooner or later, one of them is going to hit it.
Several have done so in the earlier time. Earth's thick atmosphere makes it better protected than the moon: asteroids smaller than about 35 meters (115 feet) across will burn up before hitting its surface. Nevertheless, plenty of craters exist. The Earth Impact Database in Canada lists more than 170.
Fortunately, such impacts are relatively rare, at least on human timescales. Statisticians calculate that the risk to lives and property posed by meteorite strikes are roughly comparable with those posed by earthquakes.
Fortunate for humanity that technology has advanced to the point where it is possible, in principle, to avoid such a collision. In 1998 NASA agreed to try to find and catalogue, by 2008, 90% of those asteroids bigger than 1km in diameter that might pose a threat to Earth. Any deemed dangerous would have to be pushed into a safer orbit. A nuclear blast could simply split one large asteroid into several smaller ones, some of which could still be on a collision course.
Other plans have been suggested. One is to use a high-speed spaceship simply to ram the asteroid out of the way; another is to land a craft on the rock's surface and use its engines to maneuver the asteroid to safety. A subtler method is to park a spaceship nearby and use its tiny gravity to pull the asteroid gradually off course. For now, all such suggestions are theoretical, although the European Space Agency is planning a mission, named Don Quijote, to test the ramming tactic in 2011.
These schemes offer consolation, but any effort to deflect an asteroid requires plenty of advance warning, and that may not always be available. NASA has so far catalogued only the very largest, "civilization-killing" asteroids. Plenty of smaller ones remain undiscovered, and they could inflict considerable damage.
There are tens of millions of asteroids in the solar system, and several thousand moves in orbits that take them close to Earth. Sooner or later, one of them is going to hit it.
Several have done so in the earlier time. Earth's thick atmosphere makes it better protected than the moon: asteroids smaller than about 35 meters (115 feet) across will burn up before hitting its surface. Nevertheless, plenty of craters exist. The Earth Impact Database in Canada lists more than 170.
Fortunately, such impacts are relatively rare, at least on human timescales. Statisticians calculate that the risk to lives and property posed by meteorite strikes are roughly comparable with those posed by earthquakes.
Fortunate for humanity that technology has advanced to the point where it is possible, in principle, to avoid such a collision. In 1998 NASA agreed to try to find and catalogue, by 2008, 90% of those asteroids bigger than 1km in diameter that might pose a threat to Earth. Any deemed dangerous would have to be pushed into a safer orbit. A nuclear blast could simply split one large asteroid into several smaller ones, some of which could still be on a collision course.
Other plans have been suggested. One is to use a high-speed spaceship simply to ram the asteroid out of the way; another is to land a craft on the rock's surface and use its engines to maneuver the asteroid to safety. A subtler method is to park a spaceship nearby and use its tiny gravity to pull the asteroid gradually off course. For now, all such suggestions are theoretical, although the European Space Agency is planning a mission, named Don Quijote, to test the ramming tactic in 2011.
These schemes offer consolation, but any effort to deflect an asteroid requires plenty of advance warning, and that may not always be available. NASA has so far catalogued only the very largest, "civilization-killing" asteroids. Plenty of smaller ones remain undiscovered, and they could inflict considerable damage.
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