This a repost that I made from another site. You may find it interesting.
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ASTEROID NEAR MISS: On Nov. 6th at 2132 UT, asteroid 2009 VA barely missed Earth when it flew just 14,000 km above the planet's surface. That's
well inside the "Clarke Belt" of geosynchronous satellites. If it had hit, the ~6-meter wide space rock would have disintegrated in the atmosphere
as a spectacular fireball, causing no significant damage to the ground. 2009 VA was discovered just 15 hours before closest approach by astronomers
working at the Catalina Sky Survey.
I went to the Catalina Sky Survey site and set the orbital diagram java script to the CPA of 14,000 km (0.00010 AU in the program) and worked back 15
hours. At -15 hours the distance was about 0.003 AU (448,794 km),
Orbital Diagram Java Script
At a 6 meter diameter, that's a pretty good snag at almost 500 thousand kilometers right? Well, yeah... but that is a gnats arse in astronomical
terms.
It would have been a pretty fireball, and would probably have scared quite a few goats... but if you work the angles out it can be chilling. remember,
this thing was detected ONLY FIFTEEN HOURS before closest approach.
Lets suppose that it was a 1 kilometer wide rock. Using 2009 VA's detection parameters: a 1 km wide rock would not have been seen until it was 0.5
AU from the earth.
That's half the distance to the Sun.
A 1 km rock is capable of producing a crater 6.87 miles across and would register as a seismic event of about magnitude 7.6.
Not an Earth shatterer... but if you are within 50 miles:
The air blast will arrive at approximately 244 seconds.
Peak Overpressure: 86000 Pa = 0.86 bars = 12.2 psi
Max wind velocity: 154 m/s = 344 mph
Sound Intensity: 99 dB (May cause ear pain)
Damage Description:
Multistory wall-bearing buildings will collapse.
Wood frame buildings will almost completely collapse.
Glass windows will shatter.
Up to 90 percent of trees blown down; remainder stripped of branches and leaves.
Impact Effects Program
Looking at it with the following in mind... it only takes 2 psi dynamic overpressure to rupture a house... and 3 psi to rupture your eardrums. I
highlighted that dynamic word since this applies to nuclear blasts... and asteroid impacts closely mimic some of those effects.
Now... not trying to be an alarmist... but that half an AU realistic detection distance for a 1 km wide rock seems a bit unnerving.
[edit on 7-11-2009 by RoofMonkey]
