Alex,

Sorry if my last post came across as belittleing. I was genuinely surprised by your response and couldn't really understand how a person of your intelligence could ask such questions if you had spent any time studying the issue. Based on your other comments I think we actually have a very similar view of the facts, but are commenting on them from very different points of view. You appear to be basing on your comments from the standpoint of making a scientific conclusion while I'm approaching it from more of an engineering standpoint.

You are quite right that many of Zubrin's statements and my own can not be supported as absolute scientific certainty. When I say obviously, I don't mean there is no scientific doubt about a conclusion. I mean there is too little to be worth worrying about. However, even scientists don't apply an absolute certainty criterion. All conclusions are subject to further review so by definition there is always some uncertainty in any scientific conclusion. Evolution and the Big Bang theories are two major theories with some significant uncertainties in them. Most Scientists would agree that these uncertainties do not warrant outright rejection of the theories as creationists claim. They are simply viewed as incomplete theories or the current best scientific approximation of reality. My question for you which was asked earlier, but not answered directly is how low must the uncertainty be before you consider a zero hazard to be an accurate layman's description of the risk?

Engineers routinely make design choices based on judgement rather than absolute certainty. The reason for this is not a distaste for real science (as a large portion of engineers love science as much as pure scientists), but an economic one. Engineers are tasked to design systems for minimum cost and frequently deal with issues of diminishing returns. I am quite sure this is the outlook Zubrin is using as well as he applied it ruthlessly in the design of his Mars Direct plan. He was quite willing to accept a slight increase in risk for factors of ten decreases in cost. No engineer worth his salt would ever spend large amounts of money on a system for which there is no evidence it is needed.

That is actually where we stand with MSR. The demands for extreme protective measures are driven at least in part by a post Cassini warriness of nutjobs such as Barry. While I understand Zubrin's perspective, I think he should be aware that in this case we have to make some decisions based on politics not just engineering.

The public must be comfortable with MSR or it risks being cancelled. Waging a public battle with scientists asking for modest measures as opposed to debunking DiGregorio is likely to have negative public image impact in my view and hurts his ability to build public support for manned missions. I don't think the general public understands the risks well enough to realize how low the risks really are and DiGregorio knows enough science to spin a good yarn when not confronted by those who understand how little he actually does.

Your labeling of Zubrin as a Zealot is innappopriate in my view. I will agree he is very passionate about Martian exploration and that he often looks through rose colored galsses regarding issues involved, but he is not ignoring any real evidence that Martian microbes will be hazardous.

Finally with some amusement, I'd like to address the "I read more journal than you ever will. Moreover, I have colleagues who are considered the best in the field. Admittedly, I'm no biologist, but I believe that I am just as informed as you are on the subject." comment. While I believe it is appropriate to discuss creditials with regard to third parties such as Zubrin and BD in order to assess there relative credibility, I think the content and logic of posts should be the primary basis for judging the credibility of posters. However, for the record, I think it is quite likely that you have read more jornal(s) than I (especially in the recent past) and have colleagues with more astrobiology expertise than I. But then again, as an AP bio 5 original major in biochemistry who switched to chem E, did graduate research on affinity chromatography, got a minor in molecular biology to support it, and a minor in math with enough credits in probability/statistics for another minor just because I liked the subject, it is possible I know a tad bit more about some of the issues involved than you.

Regards,
Mark