I am curious how to map the calculation onto a human impact number. 0.28% chance to hit the entire planet, most of which would have limited impact on humanity. What are the odds for example that this kills 1000 people?
You'd need to start with GIS population data for the planet, a first order answer would look at the surface area of the planet divided out by the principal destructive area size of (say) the Tunguska event, each area weighted by population.
Complications over that, once sorted out, include:
* are whether impact sites are evenly distributed across the planet or, perhaps, weight to more common near equatorial regions .. this would relate to the expected incoming trajectories of chuncky rocks which are maybe more likely in the solar plane.
* chance of impacts in non populated (or low populated) areas having a disproportionate secondary effect that kills people.
eg: Will hitting shallow ocean cause a wave that travels and kills?
Will hitting and destroying the massive water pipes that bring drinking water to New York City kill very few directly but indirectly cause the death and suffering of a million+ ?
I didn't even consider that different parts of the planet may be more or less likely to be hit. Are most of these dangerous asteroids in the normal orbital plane or could something come straight down onto the North Pole from 90 degrees? I assume yes possible, but much less likely.
If you're interested in such things you might enjoy joining your local chapter of the Global Fireball Observatory, an expansion of the original Desert Fireball Network.
