Donna Shirley: The Red Planet is again making headlines. Rovers are now exploring the surface of Mars, making exciting discoveries about the planet's environmental history. Today's exploration will help researchers of the future design habitable environments on Mars.

The Mars Terraforming Debate is co-sponsored by NASA's Astrobiology Magazine, the SciFi Museum (Seattle), and Breakpoint Media.

Terraforming was once solely the province of science fiction. In the 1930s, Olaf Stapledon wrote of electrolyzing a global sea on Venus in order to prepare it for human habitation in "Last and First Men." Jack Williamson coined the term "terraforming" in the 1940s in a series of short stories. And in 1951, Arthur C. Clarke gave the concept wide exposure with his novel, "The Sands of Mars." Kim Stanley Robinson picked up the terraforming torch in the 1990s with his epic trilogy - "Red Mars, Green Mars, and Blue Mars."

Scientists began to think seriously about terraforming in the 1960s, when Carl Sagan published several articles dealing with the possibility of terraforming Venus. Terraforming Mars has been the major subject of research of two of our panelists tonight, Dr. Chris McKay and Dr. Jim Kasting, since the 1970s.

So the question is, can we terraform Mars? How would we do it, why would do it, when we do it, and should we do it?

Chris McKay: I don't think we can terraform Mars, if terraforming is, as it was originally defined, making Mars suitable for human beings. But what we could do is make Mars suitable for life.

Human beings are a particular subset of life that require particular conditions. And it turns out oxygen in particular is very hard to make on Mars. That is, I think, beyond our technological horizons - it's a long time in the future.

But warming Mars up, and restoring its thick carbon dioxide atmosphere, restoring its habitable state, is possible. It's sort of a stretch of the word terraforming, but if you want to call that terraforming, that's possible. Bob McElroy coined the phrase "ecosynthesis" for that, and I think that's a better word.

So I'll answer, "Yes! We can bring Mars back to life." How? Well, the biggest problem is warming it up. We know how to warm up planets, we're doing it on Earth. In fact the same sorts of things would work on Mars.

Should we do it? Well, that gets down to a question that we've never had to face on Earth before: the distinction between nature and life. On Earth there is no meaningful distinction between nature and life, even in the remotest, coldest deserts.

We see that distinction for the first time when we look beyond the Earth, when we look at the moon. There's nature; there's no life. When we look at Mars, we also see nature, probably no life. It's different from the moon, and we lack the word that distinguishes between something that's dead, and something that was never alive. The moon was never alive. Mars is dead. The question in my mind is - should we bring it back to life?

Well, I vote for life. Nature's a great thing. Mars lived fast, died young and left a beautiful body - the Sylvia Plath approach to planetary science. We could play Ted and just ignore it, or we could do something better and bring it back to life. Mars is beautiful the way it is, but I think it would be even better if we could restore the biosphere that it once had. So I vote for life.

I apologize that I'll have to leave in about 15 minutes - as it turns out I'm giving a lecture at a class on ethics at Stanford on the same topic, of terraforming Mars. Who would think it would be so popular that I'd have a conflict like this?

Donna Shirley: Lisa would you like to respond to that?

Lisa Pratt: I'm afraid I'm going to have to violently disagree. I think we have no reason whatsoever to think that Mars is dead or sterile or even hostile to life forms.

I think it's increasingly evident that there is a large inventory of water on Mars. There may in fact be groundwater relatively close to the surface, meaning, within a few hundred meters of the surface. The kinds of chemistries that are suggested by the evaporite minerals indicate that the groundwater may be a brine with a perfectly habitable composition.

In fact, it may contain a soup of molecules that would be delicious for any number of Earthly microbes. So I think until we successfully interrogate the martian subsurface, and adequately address the possibility of indigenous martian organisms, that we absolutely should not think about terraforming Mars.

Donna Shirley: So Jim, if we did terraform Mars, how long would it take? What kinds of things could we do to make that happen?

James Kasting: Well, Chris has hit the nail on the head. Of course I was a co-author on the paper we wrote on that.

In that Nature paper, we defined two levels of terraforming Mars: one was for humans and one was for plants. The one that seems potentially doable, although it's difficult by itself, is to do it for plants. To me, that's not that interesting. Co-authors can disagree on what the paper implies, and I personally wouldn't go to the trouble to terraform Mars just to make it habitable for plants. I'm more interested in humans.

But as Chris already pointed out, the oxygen is a major problem. If you think about oxygen in the Earth's present atmosphere, you have to bury organic carbon. It's not enough just to have photosynthesis, you have to bury the organic carbon that you've produced. On Earth, we bury about one-tenth of 1 percent of primary productivity in the oceans, and that gives oxygen about a 4 million-year lifetime, meaning you have to do that for 4 million years.

Now, if you're really optimistic, suppose you could get oceans going on Mars, and you had as much productivity as you had on the Earth. And let's say that instead of burying 0.1 percent you could figure out how to make that system bury 10 percent of the organic carbon. It would still take forty thousand years to build up oxygen. That's a daunting task which I hardly can envision us doing. So that leaves us with terraforming it for plants, and, well, we can debate whether that's worth doing or not.

Donna Shirley: So, Greg. If we only had terraforming to make things habitable for carbon dioxide breathers, as Chris suggests, would anyone be interested in doing it?

Greg Bear: That's an interesting question, but we have to look at our motivations for terraforming Mars. Is it because we want to transform Mars for the art of doing it, for the science of doing it, or for the economic necessity of doing it?

You know, at this point, it's kind of tough imagining doing that for any of these reasons, because it would take so darn long. And usually our economic basis of doing this sort of activity requires a two-year time span for delivery of goods, so unless we start thinking very far out, like the Japanese, but hyper-cubed, then we really have to think of, well, why would we want to get this started? To leave a legacy for the next species on the planet Earth? It's about how long it's going to take. And will we be around when it's done?

If we're going to do it for an experimental purpose, then we have to define the terms of the experiment. So, it's a huge question, and we just don't have the information about either ourselves or Mars to figure out the answer to it.

Donna Shirley: So John, what information do we need about Mars?

John Rummel: I think that we're talking about the trajectory for Mars, and not necessarily as some other kind of an opportunity. Mars in forty thousand years might be a wonderful place if we started now. The question is, we can't go back when we start with the wrong propositions.

The Earth a couple of billion years ago was not all that comfortable to humans. In fact, we had bacteria that were not really happy when other organisms showed up and started breaking water (molecules), and making oxygen, and releasing it into the atmosphere.

As it's turned out, over time organisms have been able to modify this planet, not only in the atmosphere itself, but also all the way down into the mantle. Cyanobacteria are the culprits involved here; these are the organisms that caused the demise of the original inhabitants of this planet. They didn't worry about the time scale; they worried about their trajectory.

Forty thousand or fifty thousand years is the time span at which Mars terraforms itself. Mars is a place that may be terraforming on a regular basis. So get in now and avoid the rush.

We need to know, before we go, whether or not, if we adopt a trajectory, are there martian organisms there? As we push Mars towards being more Earth-like, are there organisms there that will push back, that will do what we would consider to be socially unproductive things, like covering the planet with poisons? So let's think about whether or not Mars should be pushed in that direction. Once you make the decision, then I don't have a job anymore.

Donna Shirley: I'm going to give Chris the last word here since he has to leave. So anything else you want to say about terraforming Mars?

Chris McKay: I just want to add one more point about martian life. I think that we should make a biosphere on Mars, as I said earlier. I think the ingredients of the biosphere - the genome of that biosphere - if at all possible, should be martian. That would be the most interesting situation.

We have evidence that Mars had life - we have evidence it had water, from there we deduce that it had life. I think an objective assessment of the situation leads us to be very pessimistic that that life survived intact today.

But for a variety of reasons I think we could find the relics of it - frozen and dead maybe - and reconstruct it if we had to, or find it living in some subsurface refuge, and let it once again control the biogeochemical cycles of that planet the way that life on Earth controls the biogeochemical cycles of our planet. In other words, give Mars back its heartbeat.

I'm not proposing to send life from Earth there. That's only the last resort. If Mars has no genome, then we could share ours with it. But I personally think that a Mars full of Martians is much more interesting than Mars full of Earthlings.

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