Collision of a meteorite about a mile (1.6 km) across with Earth would do enough damage to wipe out about a quarter of the human race, and events of this magnitude may occur approximately every 3 million years. Larger events happen less frequently, and smaller events occur more frequently. An estimated 50 objects with diameters of 50-100 feet (15-30 m) pass between the Earth and Moon every day, though these rarely collide with the Earth. Comets and stony meteorites of this size will typically break up upon entering the atmosphere, whereas iron meteorites would tend to make it all the way to the planet. Luckily, few of the near-Earth objects are iron meteorites.
To date, there have only been limited efforts by the nations of the world to monitor near-Earth objects and to try to prevent large meteorites from crashing into the Earth and wiping out much of the population and biosphere. NASA has estimated that there are about 2,000 near-Earth objects greater than one-half mile (1 km) in diameter and that about half of them may eventually hit the Earth. However, the time interval between individual impacts is greater than 100,000 years. If any of these objects hits the Earth, the death toll will be tremendous, particularly if any of them hit populated areas or a major city.
Collision of Earth with an asteroid only a mile or two (several km) in diameter would release as much energy as that released by the simultaneous explosion of several million nuclear bombs.
It is now technically feasible to map and track many of the large objects that could be on an Earth-impacting trajectory, and this is being done to some degree. Greater efforts would involve considerable expense to advanced societies, principally the taxpayers of the United States. NASA, working with the United States Air Force, has mounted a preliminary program for mapping and tracking objects in near-Earth orbit and has already identified many significant objects. Lawmakers and the public must decide if the calculated risk of the hazards of impacts hitting the Earth is worth greater expense. Risk assessment typically involves many variables, such as the likelihood of an event happening, how many deaths or injuries would result, and what can be done to reduce the risk. Also, other questions need to be asked, such as is it more realistic to try to stop the spread of disease, crime, poverty, and famine and prepare for other natural disasters than to spend resources looking for objects that might one day collide with the Earth. If an asteroid is determined to be on a collision course with Earth, some type of asteroid deflection strategy would need to be employed to attempt to prevent the collision.
Spaceguard is a term that refers to a number of different efforts to search for and monitor near-Earth objects. The United States Congress published a Spaceguard Survey Report, mandating that 90 percent of all large near-Earth objects be located by 2002, and some programs were funded at a level of several million dollars per year toward this goal. Present estimates are that the original goal will be met by the year 2020. One of these efforts is the Catalina Sky Survey, which discovered 310 near-Earth objects in 2005, 400 in 2006, and 450 in 2007. A loose organization of observers and astronomers in several countries meet to discuss strategies, progress, and ideas about asteroid detection through the International Astronomical Union. However, it is noteworthy that these efforts were not sufficient to detect two meteorite impacts with Earth: an explosion over the Mediterranean in 2002 and the crash of a meteorite in the Bodaybo area of Siberia on September 25, 2002. The meteorites were detected by United States military antimissile defense satellites only as they entered the Earth's atmosphere.
Societies have the technology to attempt to divert or blow up a meteorite using nuclear devices. Bombs could be exploded near the asteroid or meteorite in an attempt to move it out of Earth orbit or to break it up into pieces small enough to break up upon entering the atmosphere. Alternatively, given enough time, rockets could be installed on the meteorite and fired to try to steer it out of its impact trajectory. However, many asteroids rotate rapidly, and rockets mounted on these asteroids would not be so effective at changing their course. other proposals have been made, including firing massive missiles at the asteroid, transferring kinetic energy to move it out of its collision course. However, if the object is very large it is likely that even all of the nuclear weapons or bombs on the planet would not have a significant effect on altering the trajectory of the meteorite or asteroid. Strategies for preventing catastrophic collisions of meteorites with Earth fall into two general categories—those that attempt to destroy or fragment the asteroid into small pieces that would burn up upon passing though the Earth's atmosphere, and those that attempt to divert the asteroid and move it out of its trajectory toward Earth. In some cases it may be enough to simply delay the arrival time of the asteroid with Earth's orbit so that the planet is no longer at the place where it would collide with the asteroid when it crosses Earth's orbit. Such strategies use less energy than blasting the asteroid out of the solar system.
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This is common knowledge that disaster is everywhere. Its in the streets, its inside your campuses, and it can even be found inside your home. The question is not whether we are safe because no one is really THAT secure anymore but whether we can do something to lessen the odds of ever becoming a victim.