To let Zubrinn speak directly and in context, something you are wont to avoid:
"The November/December 2000 issue of The Planetary Report contained articles by three members of the "planetary protection" community who were apparently very upset by my article in the July/August 2000 issue disparaging the putative threat of back contamination from Mars. (See "No Threat? No Way!" on page 4.) The back contamination worthies need to deal with the following facts:

1. There's not a shred of evidence to support the notion that life of any kind exists on the Martian surface. In other words, the entire case in favor of a back contamination threat from Mars is a null set. But there is plenty of evidence to show that the putative threat does not and cannot exist, including:

* The Viking landers tested Martian soil and found it free of organic material down to an accuracy of one part per billion. Mars' dust is mixed on a global basis. If there is no organic material in the dust at the Viking landing sites, there is none in any dust on Mars.

*The landers also detected strong oxidizing agents in the Martian dust, which would destroy any microbes exposed to it. So we not only know that Mars soil is sterile, we also know why it must be sterile.

* Even in the absence of the sterilizing oxidizers detected by Viking, conditions on Mars' surface are such as to preclude active microbial metabolism. Life cannot exist without liquid water. There's no liquid water on Mars' surface.

2. If, despite all the above, Mars' surface did harbor microbial life, then it is already here. Earth receives about 500 kilograms (1,100 pounds) per year of meteorites ejected from Mars. A conservative linear extrapolation backward over the past 3.6 billion years indicates the terrestrial biosphere has already received some 1.7 trillion kilograms (3.75 trillion pounds) of samples from Mars, coming from more than a thousand different sites scattered across the planet.

There is also little doubt that sizable fractions of the ejected putative bacteria could survive the interplanetary transfer as well as reentry at Earth. (See "Life From Space" by Benjamin Weiss and Joseph Kirschvink, The Planetary Report, November/December 2000, and "Natural Transfer of Viable Microbes in Space" by Curt Mileikowsky et al, Icarus 145, 391-427, June 2000.)

3. The planetary protectors also need to explain why building a Maginot Line around NASA's tiny 500-gram (1.1-pound) sample is worthwhile, as Mother Nature continues to deliver, both ways, thousands of kilograms of uninspected and unsterilized materials.

Everyone agrees that measures should be taken to preserve the scientific value of the Mars sample. The issue is whether foundationless fears should be allowed to distort mission design so as to increase the chance of failure. NASA lost two Ranger lunar missions as a result of completely pointless spacecraft sterilization measures demanded by the planetary protection folks. As a result of their demands, in 1998 the Jet Propulsion Lab adopted a mission protocol for the Mars Sample Return stating that if a signal confirming sample confinement were lost from a returning sample craft, the return vehicle would be directed to bypass Earth.

We have already spent two decades planning a Mars Sample Return mission, and it's likely we'll spend at least another. Before we're done, at least a billion dollars will have been spent in an effort to get a sample from Mars. Yet the back contamination worthies argue that all that time, effort, money, talent, and potential for discovery should be tossed like garbage to appease tabloid fears over a nonexistent menace.

It is time that NASA rethought its "planetary protection" program. Continuing to lend credence to the irrational could be very costly indeed. -ROBERT ZUBRIN"
Interesting soil, yes.
Biological acitivity, doubtful.
Wasteful demands by BD et al, definately.
Ed