Harrison "Jack" Schmitt is the only geologist to have gone prospecting on the moon. As a crew member of Apollo 17, he was also the last person to leave footprints in the lunar soil. In part two of a two-part interview with Astrobiology Magazine editor Leslie Mullen, he talks about developing permanent settlements on the moon and Mars, and how that could change the course of human history.

Astrobiology Magazine (AM): NASA is currently designing habitation modules for future settlements on the moon. What are your thoughts about these plans?

Harrison Schmitt (HS): The current NASA approach is that the lunar base will be like Antarctica, in that people will rotate out -- they'll go there and come back. But when you look at it from a commercial point of view, where you are mining the moon for energy resources, that's a very costly approach. The least costly approach is to have people stay to live. Then you don't bear the cost of bringing them back. It's the fastest way to develop a settlement, and to have the human species moving out into space.

I think there are no disadvantages to that approach. There are plenty of people who'll say, "Yeah, I'll go there to live." There always have been and I don't think young people today are any different. The exploring will continue. Part of it's been done by Apollo, but the next people will be going as pioneers, and I think they'll go to stay. NASA should approach it that way, but I haven't convinced them yet.

AM: I think NASA plans to take it more gradually, starting with a week-long stay, then a month-long stay, and continuing from there.

HS: Maybe in order to get started you have a mission or two where you go there and come back. But we have large rockets, we know how to build spacecraft, and we certainly know how to live on the moon. I think you can form a settlement right away. Now, I say permanent settlers, but as soon as you have the capability to go to the moon, having paid for it with capital investment in energy, you're going to have a tourism capability too, at relatively low cost. And so the people on the moon can take a vacation on Earth. I discuss these considerations extensively in my book, "Return to the Moon."

AM: But then don't you have to worry about the gravity readjustment of coming back to Earth after being on the moon for a long time?

HS: I think we'll eventually know how to fix that. The one thing that we don't know, and may turn out to be true, is that one single strategy may be enough. It may reset all the body systems that would otherwise be demineralizing bone and breaking down muscle.

AM: When Astrobiology Magazine held a terraforming debate about Mars, the view was expressed that, after a few generations on Mars, the human body would adapt so much to the reduced martian gravity that settlers would be unable to come back to Earth.

HS: No. Over a few tens of thousands of years, maybe, if there's a selection for it.

AM: But the immediate adaptation to the environment, such as how gravity affects the way bones develop…

HS: Well, maybe. But again, there are ways to counter that, such as exercise. But one of the things we don't know is how much gravity the human body needs. We haven't done that kind of research in orbit. Hopefully we'll figure out a way to fly the Japanese centrifuge so we can create artificial gravity and find out what the breakpoint is. Is it one-sixth Earth's gravity? Three-eights? So it may not to be an issue on Mars. On the other hand, if it turns out to be an issue, then you look at ways of stimulating bone deposition.

As I get older, if I don't keep exercising and stressing my bones, I'm going to lose bone mass. But that's true of anybody. If you were on bed rest for two weeks, you would come out with basically the same thing as if you were weightless for two weeks. There's so much that has been going on in biomedical research here on Earth that has yet to make its way into space, so I think we're going to figure all this out. There is a tendency to try to scare ourselves, and some of that is because it's a way to get funding. Or maybe we've had too much time to think, and we just need to get operational again.

AM: That's an interesting perspective. There is that aversion to risk. I think people would really take it hard if there was a "Jonestown" on the moon or Mars. I've heard some scientists express the fear that if such a tragedy occurred, the exploration program would die right there.

Can humans someday make Mars our home away from home?

HS: The chances of that happening are higher if it's government funded than if it's investor funded. There are a lot of other motivations to maintain an investor-funded settlement, or to reconstitute a settlement. That happened in the early exploration of the United States. Settlements disappeared, and yet they still kept coming back.

AM: Because they were looking for great wealth, and there was competition with the other nations.

HS: It wasn't entirely that. Plymouth was a private enterprise. There are all sorts of motivations that drive people to explore. One of the primary motivations that ultimately settled the United States was the desire to be free of constraints. People went out to the frontier because they didn't want to be constrained by society.

The initial settlements on the moon will be constrained. We keep thinking we're going to control them, but once they reach a certain critical mass, they'll do what the original Americans did. "Taxation without representation? Forget it! And if you want your energy resources, then you're going to leave us alone!"

AM: There'll be a nation of the moon.

HS: Yes. It's with malice aforethought that I indicate a new birth of freedom, because once you start settling the moon and Mars, there's going to be a whole new thinking about the constraints that Earth imposes.

AM: Did you ever read the Kim Stanley Robinson book series, Red Mars, Blue Mars, and Green Mars? Because he discusses a lot of the societal changes you're talking about.

HS: I read parts of them. I had my students look at them for a course I was teaching at the University of Wisconson-Madison. I'm not a terraformer, though.

AM: So you want Mars left alone?

HS: Yes. I don't think you need to do it in order to establish human settlements. Plus, as soon as you terraform, you start to deplete resources very fast because Mars doesn't protect itself like the Earth does. It doesn't have an ionosphere, which on Earth protects the surface from solar radiation. Also, Mars is too small to hold onto much of an atmosphere.

We can develop the technology to live there, so why change the planet? We can inflate shelters and cover them with the Mars equivalent of the regolith. Mars doesn't have a lunar-style regolith, but it has a very fine dust. You're just going to have to get used to having a lot of sulfates around.