From Ed:
"First off, its a myth that a large asteroid or comet can not be dealt with, and dealt with with existing technologies."

My Comment:
No it is not a myth. It is the consensus opinion of the experts that have gathered together to discuss the impact threat several times. None other than Duncan Steel took you to task for this nonsense at CCNet only last month.

From Ed:
"It takes a long lead time and (gasp!) extremely large nuclear charges (150 megatons) and nuclear (double gasp!) thermal propulsion. But this is only for the largest bodies - the other smaller ones (the ones that hit most ofter) can be dealt with much more easily"

My Comment:
The protection Martian colonization provides for the future of humanity is twofold. The first is to increase our technology base as Nick and Gary mentioned to increase our ability to protect Earth. The second is to make sure we don't become extinct if a ELE impactor arrives before our technology matures to the level to deal with it. By definition these are the largest impacts. Your comments are irrelevant and contradictory to your earlier ones claiming there are no limits to our diversion ability.

From Ed:
"Second, it does not take a large impactor to kill large numbers of people - smaller ones will raise enough dust to cause climate collapse, and with a population of 6,000,000,000, a large number will starve to death - unless they resort to canibalism -"

My Comment:
That depends on your definition of small which you conveniently left out. Are you talking about < 200 m or 100 m objects as you have previously? In actuality the range in estimated for a global catastrophe ranges from 500 to 5 km with 1 km being a lower limit most experts are comfortable with. This is covered in the spaceguard report at http://impact.arc.nasa.gov/reports/spaceguard/sg_2.html#2.3 , http://impact.arc.nasa.gov/reports/spaceguard/sg_2.html#2.4 , &

From Ed:
"Third, these smaller ones have been hitting recently at a VERY HIGH RATE"

My Comment:
The experts who have estimated impact rates based on NEO populations and lunar cratering rates disagree with you. Your claim seems to be based on interpreting every potential historical calamity as an actual one without any physical evidence or acknowledging much more frequent natural disasters as possible alternatives.

From Ed:
"Nick, the way you calculated survival chances stinks.
At most we could put maybe 100-200 people on Mars. That leaves nearly all of the remaining 6,000,000,000 on Earth. Multiply the chances times the populations - "

My Comment:
Of course 200 is too small a population to matter. That is the size of a research base not a colony. Estimates for the population potential of Mars range up to 10 million. Small compared to our current total but large compared to the average human population of Earth up to a few hundred years ago. Mars never will be a replacement for Earth. It can be a preserve however.

From Ed
"Second,if we spend the money required for a manned Mars flight first on planetary defense the chances of either population dying falls to 0."

My Comment:
Nope. Read Steel's comments again. We don't have the technology. Developing the technology we need dovetails with Human exploration. I don't care which you use to justify it. If you want to develop advanced propulsion to protect against impacts that's fine with me. I'll even support it before spending on any other manned mission technology.

Regards,
Mark