2004 MN4, Even Higher Probability

Unlucky for some maybe, put Friday April the 13th 2029 in your diary.

The chance of this asteroid hitting earth is now 1 in 45. It is pretty small though – it would leave a crater about 4 miles wide, and would probably hit water, perhaps leading to a few million deaths.

On the other hand, anyone within a hundred miles of the impact would likely have a tough time. The crater will be nearly 4 miles across. Anyone within 50 miles will get 200 mph winds, a bombardment of rocks ranging from golfball size to football size, and the equivalent effects of a magnitude 6.8 earthquake. (Data from the Impact Effects Calculator, with parameters of Velocity 12.59 km/sec, 0.44 km diameter size, Dense Rock, 45 degree impact angle).

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 inversely 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.