travelling at 18mi/s and is about to strike WASHINGTON DC. AND they had 6hours of warning, how likely is the whole city going to evacuate. Will the most important people, government officials, military, politicans be safe?
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answers:
bubby say: Well I'm not going to wait to find out - I'm outta here!
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Thomas say: Wouldn't happen, as explained. But if it did, basically the President and top officials would have to get the heck out of there fast. Helicopter to Andrews Air Force Base then Air Force One and just fly at top speed.
The chance of evacuating the whole danger zone is zero. The chance of evacuating the whole of DC is near zero. Even evacuating all of Congress, if most of them are present, would be difficult.
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Raymond say: You know that we can see 8-km asteroids from over 300 million kilometers away, right? There are many in the asteroid belt between Mars and Jupiter.
If it were only 6 hours away, moving at 30 km/s (18.7 mi/s), then it would be only 6*3600*30 = 648,000 km away (twice the distance to the Moon), and would appear as bright as Venus.
6 hours before hitting Washington, it would likely be somewhere over Europe (where there are, believe it or not, telescopes and astronomers).
Everybody would already know about it.
In fact, everybody would have known about it for months. An asteroid that big would have been tracked by astronomers from many countries.
The entire government would have been evacuated to somewhere on the West coast and most of the people from the East coast would have moved there as well (although some rich ones might want to move to other continents to avoid the social mess afterwards).
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say: If we assume the asteroid is spherical in shape and take the conservative value of 8km to be the asteroids diameter and the average density of rock being 2650 kg/m^3 then, if it impacts at 18 miles/sec then it will be equivalent to 4.7 thousand million Hiroshima bombs. You would need to be on the other side of the world when it impacts although you would still hear and feel it over there too. However, if such an impact took place the aftermath would have global affects. if it broke up in the atmosphere the affects would individually be less but it would still impart the same amount of energy just not all in one place.