Space/Science — HabitableZone

Space/Science » in reply to Don't forget that damage and megatons don't scale directly

More accurate numbers...
Larry J — (archived)

can be found here

I will nonetheless attempt to add value for my readers. Turning to the 2004 MN4 Impact Risk page, we find that the asteroid's diameter is now thought to be 440 meters and its mass 1.2 × 1011 kilograms. Assuming a sphere and applying V = 4πr³/3, we find bulk density r = 0.37 g cm-3, well under half that of water ice, suggesting that either 2004 MN4 is far from spherical or that its composition is quite fluffy, like dry snow, implying that an airburst is likely.

In any case, the projected energy of impact is 2,200 megatons. Now we turn to one of the earliest posts on Arcturus, Thinking About the Unthinkable, where I used some handy equations from Arsenal to find that the 5-psi overpressure radius (which may be regarded for the purposes of this discussion as the Bad Day radius) for a 10-kiloton explosion is just over 900 meters. These things scale directly as the cube of yield, so ³√(2,200/0.01) × 0.9 km = 54 kilometers or thereabouts. The area thus affected, A = πr², is over 9,000 km², which at the average population density in the US of about 31 per km² (derived from this source) would contain about 280,000 people.

At the average population density of India -- which as I explained in my earlier post, is quite a bit nearer the probable impact site -- however, this works out to nearly 2.5 million people. Yikes.

It's the overpressure radius we have to worry about more than the size of a crater.

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