Welcome To My Nightmare
From a link which seems to have expired:
A huge asteroid is hurtling towards the Earth, threatening to wipe out entire cities.
So whatdo you do? You could try saying your last goodbyes to loved ones or you could log on to the internet to find out whether your number really is up.
I plugged in a 200 meter-wide, iron asteroid colliding with the Earth.
You can judge the impact here, a (I presume accurate) simulation from the University of Arizona.
Distance from Impact: 100.00 km = 62.10 miles
Projectile Diameter: 200.00 m = 656.00 ft = 0.12 miles
Projectile Density: 8000 kg/m3 Impact Velocity: 32.20 km/s = 20.00 miles/s
Impact Angle: 90 degrees
Target Density: 3000 kg/m3
Target Type: Competent Rock or saturated soil
And lo, energy totalling
1.74 x 1019 Joules = 4.15 x 10(cubed, while I pretend to look for the HTML superscript code) MegaTons TNT
is unleashed upon the world.
With the bonus of:
Time for maximum radiation: 0.16 seconds after impact
Visible fireball radius: 4.4 km = 2.7 miles
The fireball appears 10.0 times larger than the sun
Thermal Exposure: 6.70 x 104 Joules/m2
Duration of Irradiation: 7 seconds
Radiant flux (relative to the sun): 10.0
The major seismic shaking will arrive at approximately 20.0 seconds.
Richter Scale Magnitude: 7.0
Mercalli Scale Intensity at a distance of 100 km:
VI. Felt by all. Many frightened and run outdoors. Persons walk unsteadily. Windows, dishes, glassware broken. Knickknacks, books, etc., off shelves. Pictures off walls. Furniture moved or overturned. Weak plaster and masonry D cracked. Small bells ring (church, school). Trees, bushes shaken (visibly, or heard to rustle).
VII. Difficult to stand. Noticed by drivers of motor cars. Hanging objects quiver. Furniture broken. Damage to masonry D, including cracks. Weak chimneys broken at roof line. Fall of plaster, loose bricks, stones, tiles, cornices (also unbraced parapets and architectural ornaments). Some cracks in masonry C. Waves on ponds; water turbid with mud. Small slides and caving in along sand or gravel banks. Large bells ring. Concrete irrigation ditches damaged.
Masonry C. Ordinary workmanship and mortar; no extreme weaknesses like failing to tie in at corners, but neither reinforced nor designed against horizontal forces.
Masonry D. Weak materials, such as adobe; poor mortar; low standards of workmanship; weak horizontally.
The ejecta will arrive approximately 144.2 seconds after the impact.
Average Ejecta Thickness: 1.2 cm = 0.48 inches
Mean Fragment Diameter: 4.6 cm = 1.82 inches
The air blast will arrive at approximately 333.3 seconds.
Peak Overpressure: 24651.3 Pa = 0.2465 bars = 3.5005 psi
Max wind velocity: 48.0 m/s = 107.4 mph
Sound Intensity: 88 dB (Loud as heavy traffic)
And that's a small asteroid. From 100km away. God help us if one of the 15000m-wide variety hits.