Hi Nick -

Surprisingly, I agree, mostly.

The problem here is what happened to the comets in this analysis. We know they come in and hit, so the counts should show it, but follow these authors' logic out:

"The rate of crater formation expected from the NEAs (Near Earth Asteroids) matches the observable counts of craters from the lunar maria. (Leaving the comet flux unaccounted for - ep) Because current NEA (Near Earth Asteroid) population matches the crater counts from the lunar maria, the NEA population has been roughly in equilibrium for billions of years. In other words, new asteroids are introduced into near-Earth space at around the same rate that old NEAs are destroyed by collisions with the planets and the sun or are ejected from the solar system."

First off, the crater counts we have are very very poor, and Clark Chapman's team needs much much more money to update them.
But let's pass that by for the moment.

Now what is new and comes into the solar system is COMETS, not asteroids, as you recognize:

"I know that this is Asteroids and not comets, but it shows that the long-term flux is well-described and as discussed in the other link I referred to, 99% of the impacts are due to asteroids and other NEO's {including extinct comets, one imagines}, not new long-period comets."

The problem here is one of depletion and accretion. Some argue that most of the current asteroid population is the result of fragementationl of larger earlier planetisimals - observations on the gravitational precipitation of certain rare elements in meteorites may finally determine these parents' body sizes.

No doubt these initial asteroids have already been depeleted, "acreting" (colliding with larger planets) to a great degree since the time of the formation of our solar system. To compensate for this depletion, we must then have the entry of long period comets. Here the language is difficult, as the term "asteroid" sometimes is used to refer to "dead" (volatile depleted) comets, but if the combined impactor flux over time is constant, and the initial asteroid population is depleted, then one must have an increase in cometary flux.

"If the flux of long period comets is uneven, then it logically follows that the risk can only be greater than average for a fraction of the time, which diminishes as the rate goes up, so there is no credible risk of a "storm" of comets impacting the Earth on a human timescale."

Actually, if we are heading into a cyclical period of higher than usual flux, then we are headaing into a cyclical period of higher than usual flux - remember also that these things break up, and the fragments are then in turn subject to gravitational perturbation.

The data appear to indicate that we just recently got hit pretty hard by fragments from Comet Encke.

"I must say I've never heard of Cold Duck, but I'll wager you a crate of it, or an equivalent of your choice in 2030."

Hmmm, seems to me that since you place the odds are so low, I could ask for a considerable multiple in your pay off and you wold still take the wager...

By the way, Greenland got hit just a few years back, but the only thing "killed" was ice and snow... could we include the very recent past couple of years in that wager?

"Don't belittle your life expectancy - you should outlive your parents and have a significant evanescance, waiting for the sky to fall - which it won't!"

Thanks for wishing me a long life. I won't be waiting for the sky to fall, but instead remembering when it has earlier...

ep