Forgive me, but in the interest of bandwith I've snipped some of your post.

Mark Eby wrote:
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.

Alex writes:
That is a fair assessment, but in fairness, the issue of Planetary Protection is not simply an engineering one. At any rate, my undergraduate degree was a Bachelor of Sciences in Aerospace Engineering, then I transitioned over to "Pure Science" ;-) with a MS in Geology and a PhD in Planetary Sciences. Although I never pursued my Professional Engineers (PE) license, I do understand the world of engineering.

Mark Eby wrote:
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?

Alex writes:
Just to be clear, I am in full support of a Mars Sample Return mission (in fact, this past January I attended a CNES-sponsored workshop at the University of Lyon on that very subject) and think the risks of back contamination are very low, BUT NOT ZERO. I feel that the lunar experiences may have engendered a false sense of security, especially given that Mars is a totally different, largely unknown world from a biological standpoint. However, I feel that the planetary protection problem is eminently manageable with current or near-term (not to mention affordable) solutions, but cannot be dismissed out of hand, which in my opinion Zubrin is trying to do.

Mark Eby wrote:
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.

Alex writes:
Agreed, but forgive me, I do not intend this as an insult, but I will not shade the truth, even slightly in the interest of expediency, because the public does not understand the nuances between 0 and 1.3x10^-5. While ignoring the distinction may be "good enough for government work", it is not good enough for Science. Sorry, if that's a flaw on my part then so be it.

Mark Eby wrote:
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.

Alex writes:
The crux of the problem as I see it is that there is no "real evidence" one way or the other whether putative any Martian biota poses a threat to Earth. Despite the plethora of "astrobiological" publications, you'd be surprised at how (in my opinion) the entire field of study has a sort of house of cards quality to it. One assumption can generate dozens of models, which in turn beget dozens more. I've seen to many other models in other fields of study overturned by one discovery. To think that something similar is not possible regarding the risks associated with back contamination from Mars is, I believe, short sighted.

Mark Eby wrote:
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.

Alex writes:
Agreed.

Mark Eby wrote:
... it is possible I know a tad bit more about some of the issues involved than you.

Alex writes:
Undoubtedly, and I meant no disparagement to you or your knowledge. I was just reacting to your question "Read anything on astrobiology?", which I found slightly amusing because the fact of the matter is that I am constantly in possession of a published article or reading a draft of someone else's work for peer review. Personally, I do not like it when others throw around credentials, and try to avoid the same. Indeed, I've received tremendous insights into certain areas from complete novices (e.g. undergraduates ;-) and conversely have found many postdocs to be woefully uninformed on certain subjects admittedly within their ken. As for who reads what, I'll mention offhandedly that the following is a list of journals that, at a minimum, I must read and comprehend on a weekly, monthly, and quarterly basis WITHOUT FAIL to stay current in my field:

Science
Nature
Icarus
Journal of Geophyscial Research-Planets
Journal of Geophysical Research-Space Physics
Geophyscial Research Letters
Eos
Geology
Geological Society of America Bulletin
Journal of Geology
Geochimica et Cosmochimica Acta
Planetary and Space Science
Earth and Planetary Science Letters
Space Science Reviews
METEORITICS & PLANETARY SCIENCE
Proceedings of the National Academy of Sciences
Astrobiology
Cell
Origins of Life and Evolution of the Biosphere

Not to mention the hundreds, if not thousands, of conferences proceedings and extended abstracts.

Alex R. Blackwell
University of Hawaii