Friday, December 14, 2012
Another day, another close shave - an asteroid called 2012 XE54 was discovered less than a week ago, just two days before it passed by us at a distance of just 230,000 km. This one was also fairly large, with a diameter of 36 metres. That's a surface area of 4100 m2, or a football field and a half (or 1.5 acres).
Asteroids under 10 metres or so in diameter tend to burn up in the atmosphere on the way down, which is a good benchmark for whether an asteroid could actually be dangerous or not. This one would do the following if it impacted 10 km away:
The projectile begins to breakup at an altitude of 54000 meters
The projectile bursts into a cloud of fragments at an altitude of 12400 meters
The residual velocity of the projectile fragments after the burst is 7.68 km/s
The energy of the airburst is 8.43 x 1015 Joules = 2.01 x 100 MegaTons.
No crater is formed, although large fragments may strike the surface.
The air blast will arrive approximately 48.2 seconds after impact.
Peak Overpressure: 4350 Pa = 0.0435 bars = 0.618 psi
Max wind velocity: 10.1 m/s = 22.5 mph
Sound Intensity: 73 dB (Loud as heavy traffic)
Nothing apocalyptic. A hit from an asteroid about 20 metres in diameter discovered a week before impact would be ideal, in my opinion.