If the newspapers and grant-seeking boffins are to be believed, it's only a matter of time before an enormous lump of rock comes hurtling out of the heavens and puts a serious downer on everbody's day.

Not satisfied with having wiped out the dinosaurs, asteroids are apparently hungry to inflict more terrestrial mayhem - and next time humanity itself could be on the menu.

We're obliged, therefore, to the Department of Planetary Sciences at the University of Arizona which has developed a handy programme to calculate to what extent said apocalypse will immediately effect you, the innocent bystander.

The Impact Effects programme allows you to enter parameters such as your distance from impact, size of asteroid, etc. You then get told what happens next. Intrigued, we decided let the "impactometer" calculate the effect of a 50m ball of rock falling on not-too-distant Shenfield (a commuter town in Essex's commuter hinterland in need of "redevelopment" - asteroids take note):

• Distance from impact: 50km
• Projectile diameter: 50m
• Projectile density: 3000kg/m3 (dense rock)
• Impact velocity: 17 km/s (average for an asteroid, apparently)
• Impact angle: 15
• Target density: 1500kg/m3 (porous rock)

The programme then offered us the following:

Energy:

• 2.84 x 1016 Joules = 6.78 MegaTons TNT
• The average interval between impacts of this size somewhere on Earth is 480.1 years

Crater Size:

• Transient Crater Diameter: 867 m = 2845 ft
• Final Crater Diameter: 1353 m = 4438 ft
• The crater formed is a simple crater

Thermal Radiation:

• Time for maximum radiation: 0.04 seconds after impact
• Visible fireball radius: 0.4 km = 0.3 miles
• The fireball appears 1.9 times larger than the sun
• Thermal Exposure: 3.24 x 102 Joules/m2
• Duration of Irradiation: 1 seconds
• Radiant flux (relative to the sun): 0.4

Seismic Effects:

• The major seismic shaking will arrive at approximately 10.0 seconds.
• Richter Scale Magnitude: 5.2
• Mercalli Scale Intensity at a distance of 50 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.

Ejecta:

• Most ejecta is blocked by Earth's atmosphere

Air Blast:

• The air blast will arrive at approximately 166.7 seconds.
• Peak Overpressure: 4362.3 Pa = 0.0436 bars = 0.6194 psi
• Max wind velocity: 9.2 m/s = 20.5 mph
• Sound Intensity: 73 dB (Loud as heavy traffic)

Blimey. A blast equivalent to 6.78 MegaTons of TNT making a 867 metre crater? That's Shenfield permanently off the map, make no mistake.

Interesting stuff, although we can't help feeling that those of us who have studied the asteroid threat in depth should be allowed a further input option: Deploy Bruce Willis? Y/N?

Pressing "Y" would, of course, would be an end to the matter. ®