01-19-2007, 05:34 PM
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Too lazy to set a custom title
Join Date: Jul 2002
Posts: 40,377
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Quote:
Originally Posted by Alky
What I don't understand is from this site: http://neo.jpl.nasa.gov/torino_scale.html
Level 8
but then on the other link posted in the thread, for the next hundred years it shows only the maximum on the Torino scale as 1.
Seems a bit off if you ask me... |
The thing is that not all asteroids has been discovered. From the ones that has been discovered, there's currently no real risk that one of them will hit Earth in the 21st century.
check out this page for more explanation about NEO'S - Near Earth Objects
http://impact.arc.nasa.gov/intro_faq.cfm
some quotes:
Quote:
What size NEOs are dangerous?
The Earth's atmosphere protects us from most NEOs smaller than a modest office building (40 m diameter, or impact energy of about 3 megatons). From this size up to about 1 km diameter, an impacting NEO can do tremendous damage on a local scale. Above an energy of a million megatons (diameter about 2 km), an impact will produce severe environmental damage on a global scale. The probable consequence would be an "impact winter" with loss of crops worldwide and subsequent starvation and disease. Still larger impacts can cause mass extinctions, like the one that ended the age of the dinosaurs 65 million years ago (15 km diameter and about 100 million megatons).
How many NEOs exist?
There are many more small NEOs than large ones. Astronomers estimate that there are approximately 1100 Near Earth Asteroids (NEAs) larger than 1 km in diameter, and more than a million larger than 40 m in diameter (the approximate threshold for penetration through the Earth's atmosphere).
Are any NEOs predicted to hit the Earth?
As of the end of 2004, astronomers had discovered more than two thirds of the larger Near Earth Asteroids (diameter greater than 1 km). None of the known asteroids is a threat, but we have no way of predicting the next impact from an unknown object.
What is the risk of impacts?
We don't know when the next NEO impact will take place, but we can calculate the odds. Statistically, the greatest danger is from an NEO with about 1 million megatons energy (roughly 2 km in diameter). On average, one of these collides with the Earth once or twice per million years, producing a global catastrophe that would kill a substantial (but unknown) fraction of the Earth's human population. Reduced to personal terms, this means that you have about one chance in 40,000 of dying as a result of a collision.
How much warning will we have?
With so many of even the larger NEOs remaining undiscovered, the most likely warning today would be zero -- the first indication of a collision would be the flash of light and the shaking of the ground as it hit.
What about smaller, more frequent impacts?
The Spaceguard Survey and most associated search and tracking programs are concentrating on NEAs larger than 1 km in diameter -- large enough to risk a global ecological catastrophe if one of them hit the Earth. But there are many more smaller undiscovered NEAs, and we are likely to be hit somewhere on Earth by one of these, with an energy equivalent to a large nuclear bomb, sometime in the next couple of centuries. The last such impact was in 1908 in Tunguska ( Siberia ) with an estimated explosive energy of 15 megatons. In 2003 NASA completed a study of these sub-km impacts and concluded that it was both technically feasible and cost-effective to to mount an expanded Spaceguard Survey, with much larger telescopes, to search for these smaller asteroids.
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I don't use ICQ anymore.
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