And if you don't think that, then you try and figure out something more universal that life might do to its environment that you could look for. Or maybe you do a little of both. I'm curious what the panelists think about how we should be approaching that, and how what you think we should be doing compares to what NASA and ESA are doing.

Pam Conrad: That's a very good question to ask, especially in the context of what Pascal had to say. You don't want to blow your opportunity. So, there are two answers to your question. First, let's take a quick look at why we're still arguing about the results for Viking. The people who did Viking went to great lengths to try to achieve consensus in advance of the experiment regarding the criteria that would determine a positive result or not.

The problem is, in trying to characterize the results of only a couple of samples, at least from what I've observed on Earth in the field, using pretty sophisticated life detection techniques, there are heterogeneous distributions of the evidence of life in the environment. I can look with any kind of a probe at a spot that's 50 microns wide, and see absolute definitive evidence of Earth life, and I can move two millimeters away and see absolutely no evidence. If I look five times, maybe 60 percent of the time I'll see the evidence. So what I have to define is a search space, and a statistical probability that I will observe the evidence within a certain volume or a certain surface. That's just one set of parameters.

The second set of parameters has to do with the next part of your question, which is, how do you recognize that the life that you know or the life that you don't know as distinct from the environment in which it may reside? And that requires that you understand the planetary materials.

My approach, as a dumb geologist, is I'm going to try to understand everything I can about the environment, everything I can about the thermodynamic propensity to form one set of phases relative to another, and the kinetic properties of that specific environment. And then I'm going to look at environments on Earth -- because really that's the only sample that we have here -- and try to discover how environments that have been affected by living things might weather differently, or might go through time differently than those environments that have had a more minimal effect of biology. And that's tough here, because life is everywhere. But at least one can begin to discover a trend.

Now, as for how we might recognize the effect of life as we don't know it, I don't have a clue. But I do know this. I am desperate to go explore another planet and look to see if we are alone or whether there's somebody there. And so what you have to do is just say, Ok, I'm going to plunge in at the problem on one spot. And I'm going to see where I fall short in that one regard, and then modify the next experiment.

It's a damn shame that it has taken so long since Viking to send life detection experiments back to Mars. Or that I have friends who don't believe we really went to the moon, because they didn't see it happen. Or that I know children who don't even know that we did go to the moon.

This is ridiculous! We could be Star Trek. We know how to do a lot of stuff. And as Pascale said, there's still a lot of stuff that we don't know how to do. But even though it's entertaining to sit here and discuss what we do and don't know, and to opine about information as life, or I like to think about life as just the commerce of electrons, the real nitty gritty, the nuts and bolts of how we would find life on another planet -- it isn't comic books, this stuff is really happening! I recognize a lot of you out there, and I know that you're all working on life detection instruments. I think we can get there. But we have to agree that, when we're discussing what we know about life so we can do the measurements, we will concede that there are measurable parameters that we can agree upon a positive and a negative result.

In the context of this debate, this is for fun, just to discuss what we can imagine out of our own brains about what life might be like if it were not so Earth-centric.

Steve Benner: I agree with that. The Viking 1976 experiments were designed by Joshua Lederberg, Norm Horowitz and Gil Levin, excellent outstanding molecular biologists. They should have been designed by organic chemists, and that was a paid political announcement brought to you by the American Chemical Society - and a card-carrying member of that.

One of the problems with life detection on Mars was that the 1976 experience contaminated the history of designing life detection. What's quite clear is that we have to throw at Mars whatever we can get in terms of sophisticated chemical analysis and instruments.

Every paper that I write, I say that it makes absolutely good sense for pragmatic reasons to follow the water, not because I can't conceive in an atmosphere of a life form that lives in ammonia or supercritical hydrogen helium fluids, but because it's the most likely way to not only find life, but to be able to recognize it if we do find it. It's hard enough to design something to find life in water. I couldn't even begin to design something to detect life that's a little bit different chemically from what we know.

So this discussion, from my perspective, has nothing to do with the pragmatic design of flights to Mars in the next ten years, or whenever we might be able to get one that lands successfully without crashing at 300 kilometers an hour. So the bottom line is while this discussion this is fun, this is not prescriptive at this point for the design of NASA missions.

What is prescriptive is that it makes absolutely good sense to get to wherever you can find liquid water in subsurface Mars; get there as fast as you can with as much instrumentation as you can. I only wish that we'd had a laser Raman spectrometer at the Opportunity rover site, because I'm quite convinced we would have found the borates that we think are important for making carbohydrates, or mellitic acid as an organic by-product from meteorites, or perhaps even ribose there. We're under-equipped for what we are trying to do, and we shouldn't take our eye off the ball to go after weird life when we're not doing a good job of finding the kind of life, and the organic molecules, that we most expect to find.

+ Part I of this debate: "Launching the Alien Debates"
+ Part II: "The Dialectic Game"
+ Part III: "What is Life?"
+ Part IV: "The Basic Rules of the Universe"
+ Part V: "Debating Life's Boundaries"
+ Part VI: "Strange and Alien Forms"

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