Since I have not slept for over 36 hours, this is as good a time as any for me to spare you a few minutes of my time to explain to those interested some of the fallacies underlying the concept of "Lifeboat Mars.

First, I'd like to thank Nick Hoffman for endorsing the idea of placing the priority of spending on NEo detection telescopes ahead of that of spending on manned Mars missions, or a Martian colony.

That said, let's start. It is widely assumed that impacts of the Earth and Mars are statistically separate - in other words, if one planet gets hit, it in no way bears on whether the other planet will get hit. In point of fact, it is highly probable that the chances of either planet getting hit co-vary, at an extremely high level of confidence.

This has to do with the impact mechanism. Our solar system is often viewed as a star and 9 (more or less) planets with just an occasional odd rock or dirty snowball thrown in.

In reality, think of our solar system as a mix with some larger accretions, which we think of as planets. It appears that when we pass through an arm of our spiral galaxy, the Milky Way, gravity works to stir this mix up. Whether the course of impacting objects is changed, or whether gravity simply changes the planets' positions relative to this mix, is not certain at present. In addition to this there is also a separate gravitational effect when our solar system passes through the plane of our galaxy, the Milky Way, though againg the mechanisms are not well understood at this time, and both mechanisms have been proposed.

What is clear from the evidence on Earth is that both gravitational processes are operative, the first on a 100 million year basis, and the other on a 26 million year basis. Note that in regard to either gravitational effect the planet Mars should be affected simultaneoulsy in nearly exactly the same way as the planet Earth: by either process, it most likely will get hit at roughly the same time, on a geological scale.

It is further assumed by proponents of "Lifeboat Mars" that due to Mars' lack of atmosphere and athonosphere the consequences of major impact would be far less lethal to human beings there, than the consequences of such an impact with the Earth. Given the vast potential energy held in Mars' CO2 reserves, this is by no means certain.

In closing this note, if I remember correctly, we "just" (5 million years or so ago) passed through an arm of the Milky Way.

EP