In April 2029, an asteroid called Apophis will come within five Earth radii - below the orbits of geosynchronous satellites. Astronomers have already calculated the exact orbit and know the asteroid will not hit the earth (this time).
There are theories that the dinosaurs were killed off by a big collision millions of years ago, and that large mammals went extinct due to a smaller collision 13,000 years ago. There was a serious impact in Siberia in 1908. So the world is now going to try to map the near earth orbit (NEO) objects with the hope that if one is on orbit to collide with earth mankind will be able to do something about it,
JPL has already found 763 asteroids and 82 comets in NEO that are more than one kilometer in diameter; it believes that there represent 90 percent of the total. A new program is under way to log NEOs as small as 140m (460ft) in diameter; the target is to find 90% of them by 2020.
An object is classed as an NEO if it comes within 45 million km (28 million miles) of Earth's orbit.BBC reports:
A major success was the first ever accurate prediction of an Earth impact, last October. The Arizona observatory spotted a two-metre space rock heading for Earth and predicted exactly when and where it would land. The rock exploded in an empty part of northern Sudan, within a day of discovery.Comment: This situation reminds me of the bird flu situation. In both cases it seems likely that a very deadly event will occur in the future, but that event is very unlikely to happen in the next year. Prudence suggests we seek to measure the danger and prepare to avoid disaster when it threatens imminently, but we must balance danger and the cost of its prevention against other risk amelioration resource allocations. JAD
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