MR. STEVE ROBERTSThanks so much for joining us. I'm Steve Roberts of the George Washington University sitting in today for Diane Rehm while she's away on vacation. Science journalist Stephen Petranek has a prediction. By the year 2027, astronauts will land on Mars. By the year 2050, a colony will be flourishing on the red planet. How will humans get there and who will want to go?

MR. STEVE ROBERTSWhen we land, how will we breathe? What will we eat? Can we survive there? These are some of the penetrating questions Petranek explores in his new book, "How We'll Live On Mars." Stephen Petranek is the former editor and chief of "Discover" magazine. His TED Talk, "10 Ways The World Could End," has been watched by more than 1 million people. Stephen Petranek, welcome to "The Diane Rehm Show."

MR. STEPHEN PETRANEKThank you. It's a pleasure to be here.

ROBERTSAnd you can join our conversation if you've seen Steve Petranek's TED Talk or heard about some of his other work. I'm sure you'll have plenty of questions so please join in. 1-800-433-8850. Or, of course, you can email us at drshow@wamu.org or post on Facebook or on Twitter. Okay. So as I said, 2027, that's your prediction. I suppose most people listen to us and say, you know, what's he talking about? Why are they wrong and what's behind this prediction?

PETRANEKI know it sounds fantastical to lots of people that humans will land on Mars in as little as a decade or just a little more than a decade. But what I tried to do in this book is basically a reporting exercise on where we are in space travel, which is not very far. We haven't gone very far in the last 50 years. We can't even get back to the moon. And where we're going.

PETRANEKAnd the vision of landing on Mars in 2027 comes from Elon Musk, who's the CEO of SpaceX and also the CEO of Tesla and also the chairman of a solar rooftop company. And...

ROBERTSAnd a very, very rich man.

PETRANEKWell, it, you know, he has poured almost his entire fortune into SpaceX and SpaceX is an upstart company that makes rockets and Elon Musk, since -- for many, many years has had a singular vision. It's the same vision that Wernher Von Braun had, who is responsible for getting the Apollo astronauts to the moon, and that vision is I want to see people on Mars. And his reasoning is very interesting because his reasoning is that there are many threats to civilization on earth.

PETRANEKYou know, they could be -- you could wake up tomorrow morning and look in The Washington Post or the New York Times and see a headline that says "Amateur Astronomer's Discovered 10-Mile Wide Asteroid Near Jupiter On Collision Course With Earth" and there's nothing we could do about that and it would probably kill everything on Earth larger than a rabbit.

PETRANEKAnd there are many other threats to our existence on Earth as a species so Musk is determined that the human species and all it has accomplished, its extraordinary civilization and its extraordinary culture will survive on another planet.

ROBERTSSo that's really the main inspiration you describe in your book as an insurance policy.

PETRANEKCorrect. It is an insurance policy. The human species eventually has to leave Earth because our sun will begin to expand in a couple of billion years and when it does, it will throw Earth out of orbit or it will completely annihilate all life on Earth with radiation. And if we do not become a space-faring species, we will not survive so we must go to Mars. Mars is the first step. The moon is not a step.

PETRANEKEven Von Braun didn't want to go to the moon. He actually wanted to go to Mars in the '60s. And as fantastical as all this seems, we've had the technology to do this for more than 50 years.

ROBERTSBut, you know, you use an interesting word, "space-faring" and also in your book, beyond this question of survival and insurance policy, you also talk about the lure of the unknown, that the human species has always been drawn to new frontiers and that they're -- this is part of almost the mythology, the culture of discovery beyond the practical benefits.

PETRANEKI think it's more than being part of our culture. I think it's probably in our DNA. I think it's probably in our genes and I'll tell you why. Humans evolved in Africa 2 million years ago and not very long ago, they started immigrating out of Africa into other parts of the world and they have moved and moved and moved through every continent, across every sea to finally populate the entire world.

PETRANEKAnd that need to move beyond the horizon and see what's over the next hill seems to be built into us and this is really interesting. It may actually be a form of survival.

ROBERTSIn what sense?

PETRANEKIn that if you're originally a hunter/gatherer and you eliminate most of the wildlife and what you can eat where you are, then you move across the horizon to the next hill to see what's beyond and then you forage and you live there. So if that's the way we developed, then it's in our DNA to keep moving on to survive. And, in fact, it's an accurate representation of reality for us, because if we do not get at least to Mars and then go beyond that, humans won't last forever. We'll become extinct.

ROBERTSWell, you and I, as we were talking just before we went on the air, both products of the immigration impulse, your ancestors going from Czechoslovakia to Iowa, mine from Poland and Russia to New Jersey. I mean, we -- both products of that. We're here in America today for those reasons.

PETRANEKYes. Humans move on. They're explorers. They're adventurers. But it's not just some kind of weird cultural attribution. I actually think it's part of our survival mechanism.

ROBERTSNow, one of the things you talk about in the book is that, while you talk about the first mission maybe in 2027, you say that the long range plan of Elon Musk is not just to visit. It's to colonize and that by 2050, if these plans work, that there actually will be people living there.

PETRANEKOne of the most shocking conversations I've had in my entire journalistic career was with Elon in January and he had been widely reported as saying that eventually, he thought there would be 80,000 people living on Mars. And I just happened to kind of mention that in a sentence. It wasn't even something I was going to ask him about. And he said, oh, no, no. Everybody's gotten that wrong.

PETRANEKWhat I meant was that 80,000 people would go to Mars all at once. So here's his scenario. His scenario is, he will be "deeply disappointed," and that's a quote, if he has not landed humans on Mars by 2030. But then, in the 2030s, in the early 2030s, he imagines having hundreds of reusable rocket ships, each of which will carry 80 to 100 people at once so you will have thousands of people, as early as the early 2030s, going to Mars.

PETRANEKAnd by 2050, at a minimum, he imagines 50,000 people being there. But here's the kicker. By 2050, he imagines having close to 1,000 ships that can make the voyage to Mars at once with 80 to 100 people aboard so that's 80,000 people per trip. As he says, you can't have a civilization if you don't have lots and lots of people. So he's building a system to get lots and lots of people to Mars far sooner than anyone can guess.

ROBERTSOne of the -- this is a deeply ironic statistic that the projected travel time to Mars, 243 days, almost exactly the same travel time it took the original colonists to come to America by ship.

PETRANEKActually, the original immigration to -- at least of, you know, white Europeans to the Americas in the 1600s is remarkably similar to the voyages we're going to making to Mars in many, many ways. The actual cost of making those voyages for individuals, the actual time frame that it took for them to get there, the kind of hostile environment that they find themselves in -- actually it was a heck of a lot easier to live in colonial America.

PETRANEKBut most of the early colonists died and they died very quickly, you know. Eighty percent of the people who went to Jamestown in the early 1600s were dead in two years.

ROBERTSNow, we're already getting some tweets and you raise this issue in the book, you confront it, that the single biggest threat to these plans is the nature of Mars, its very thin atmosphere, which makes it a very dangerous place for humans. Talk about that issue and how plans are evolving to deal with it.

PETRANEKThe first thing to understand is that of all the planets, even though Carl Sagan, many, many years ago proposed that we could actually terraform Venus to be habitable for humans, but of all the planets in our solar system, and we can't really imagine at this point leaving our solar system yet, but of all the planets in the solar system, Mars is, by far, the most habitable. And yet, it's an awful place for humans.

PETRANEKThere's extraordinary radiation. There is a lot of water on Mars, but it will be difficult to get a hold of and to use. There's no oxygen. The atmosphere is 96 percent carbon dioxide so you can't breathe. It's incredibly cold. Temperatures can actually be as high as 70 degrees Fahrenheit at the equator in the Martian summer, but a night they go down to minus 50 to minus 100 degrees. So it's a lot like living in Antarctica.

ROBERTSYou know, I was struck by that. You were -- that as you described the potentials for colonization, it sounded like life in Antarctica.

PETRANEKIt is a lot like life in Antarctica. In fact, there are two places on Earth that are very kind of Martian in their environment. One is high volcanoes in Hawaii, kind of high desert volcanoes, and barren fields in Antarctica that are mostly rock.

ROBERTSThat’s Stephen Petranek. His new book, "How We'll Live On Mars." I'm Steve Roberts sitting in for Diane. Give us a call, 1-800-433-8850. We'll get to your calls and with Stephen Petranek as soon as we come back. Stay with us.

ROBERTSWelcome back. I'm Steve Roberts sitting in today for Diane. And my guest this hour is Steven Petranek, well-known science journalist that gave a TED talk that perhaps some of you have seen on the 10 ways the Earth could be destroyed. But his new book is called "How We'll Life on Mars." And we've been talking about some of the practical questions. And given the fact that it's such an inhospitable atmosphere -- as you say, far more dangerous than the New World was to settlers at Jamestown -- what are some of the -- are people already thinking about how you would create an environment that was -- that is -- humans could inhabit.

PETRANEKActually, to NASA's great credit, it has developed extraordinary systems that would support humans on mars for many, many years, despite the fact that it has had zero plans to go to Mars for many years, or not that it would say publicly. It has really worked out -- or at least to send humans to Mars -- it has really worked out very carefully some of the problems that we would face on Mars. For example, there's been a lot of research done with habitats.

ROBERTSHmm.

PETRANEKThere's been a lot of research done with throwing seven people into a small container for a year at a time and seeing how they react with each other. NASA has developed a machine called MOXIE, which is going to go up on the next version of the curiosity rover in 2020. And it's a machine that take the carbon dioxide atmosphere of Mars and turns it into oxygen. And it's kind of interesting to think about carbon dioxide for just a second. It's about 78 percent -- or about 72 percent oxygen. So there's two oxygen atoms and one carbon atom. And if you can split that carbon atom off, what's left is pure oxygen.

PETRANEKSo even though Mars' atmosphere is extremely thin, it's only 1/100th the atmosphere density of what we have on Earth, there's a lot of oxygen there. And they've invented this machine that can suck the oxygen out of the Martian atmosphere.

ROBERTSAnd you -- again, we understand this is all theoretical -- but people are working on it. And one of the things you say is, look, Americans -- certainly a lot of Americans used to living -- human beings used to living indoors and that that's basically what you'd have to do on Mars. That you would have to live, probably in the beginning, underground or in caves to shield yourself from the radiation. You would have to wear special suits all the time. Talk about that.

PETRANEKWell there's -- the biggest problem of living on Mars is not -- to live on Earth, you need food, shelter, water and clothing. To live on Mars, you need food, shelter, water, clothing and oxygen. And the biggest problem on Mars actually is radiation. Because you'll be -- because the atmosphere is so thin, you won't have the protection of the atmosphere density that we have on Earth from solar radiation, from the particles that are shooting at us all the time from the sun. You don't have the Van Allen belt that Earth has to protect itself. And you don't have a magnetosphere that is caused by our molten core that is a kind of a magnetic shield around the Earth that deflects a lot of solar particles.

PETRANEKSo the amount of solar radiation on Mars is going to be a very significant factor. Solar radiation is relatively easy to deal with if you just have thick walls on the building you're living in. So we could conceivably construct habitats on Mars, probably made out of bricks that are made from the soil on Mars. And NASA has a solution for that. They have a formula for adding a little plastic to the Martian regolith, the soil there and throwing in a little water and putting it in a microwave-like device and it makes a brick. But the more practical way of living on Mars in the beginning will be to live in lava fissure tubes which probably exist in a lot of places on Mars, or to simply find a cave or to build a habitat underground.

PETRANEKAnd that's primarily because there's another form of radiation on Mars that people will be exposed to which is really, really deadly, which is cosmic rays. Cosmic rays are mysterious in origin. We don't know where they come from. But they come in sort of a steady stream of dribs and drabs. Transcontinental pilots on Earth get exposed to a lot of cosmic radiation...

ROBERTSHmm.

PETRANEK...as do people who live high in the Rocky Mountains. But on Mars, there will be almost zero protection from cosmic radiation. And this stuff is really powerful. To give you an analogy I once heard, is that a particle -- or a wave of cosmic radiation that is equivalent to, say, the weight of a proton -- and cosmic radiation is basically pieces of atoms being thrown at you at high speed -- something the size of a proton that's cosmic radiation that comes at you would have the energy of a baseball traveling at 20,000 miles an hour. So cosmic radiation can pierce even 10 feet of steel.

ROBERTSWow.

PETRANEKSo people will have to be very careful about protecting themselves from cosmic radiation.

ROBERTSNow, you mentioned NASA several times and the work they have done in terms of developing systems that could help make Mars more inhabitable. But you also mentioned that for 50 years they sort of put plans aside. Wernher von Braun wrote in 1952 about Mars. But you write in your book about how a decision was made during the Nixon Administration to focus more on the shuttle program. And that the technology is there but it's never been pursued. Talk about that history and why that decision was made.

PETRANEKWe made an extraordinarily bad decision in the early '70s. One of the things people may not understand is that NASA reports to the President of the United States. It's an administrative function. In the early 1970s, the Apollo program was coming to a close. Everybody was running around at NASA saying, "What are we going to do next?" And there were two major proposals at the time. One was the space shuttle, which was to be a small, reusable rocket plane that could be sent into space and then fully recovered. And that would make it cheap to get into space, or at least into Earth orbit. And then you could do things in Earth orbit, like build a rocket to go to Mars.

PETRANEKInstead, the military and the intelligence agencies got involved in the space shuttle. And Nixon made the decision, even though von Braun was saying, "We should go to Mars next." And he was proposing that NASA -- we already had the rocket to do it, the Saturn V, the largest most magnificent machine ever built by human beings. We had the rocket to do it. We had the technology to do it then. And he said, "We will put humans on Mars by 1985." Instead, Richard Nixon chose to go with the space shuttle, I think largely for military and intelligence reasons. Because at that time, most of our spy satellites, for example, used film. And the film had to be ejected out of the satellite and then captured and it was a very cumbersome process.

PETRANEKAnd the funny thing is that everything NASA does -- it's not funny, it's weird -- everything that NASA does is supposed to be in the public realm. For example, they published all of the plans for building the space shuttle and the Russians went out and built one. But from 1982 to 1992, there were 11 secret missions of the shuttle. And of course, the military found out by requiring a much larger shuttle than NASA had originally proposed. The military discovered that launching this thing and recovering it and refurbishing it was really expensive. And it turns out that the 135 flights that the shuttle made cost an average of $1.4 billion every time it went it.

PETRANEKAnd that limited, at the same time that NASA's budget was being squeezed, that limited what NASA could do. So it couldn't do two things at once. It couldn't have a space shuttle program and human missions to the moon or to Mars.

ROBERTSNow, I think we have Jim Green on the line. Mr. Green, are you there?

MR. JIM GREENYes, this is Jim Green.

ROBERTSJim Green is director of NASA's Planetary Science Division. And you just heard Stephen Petranek talk about NASA's role here. And I gather that in -- recently, NASA has stepped up its focus on Mars. Give us an update on what your goals and plans are.

GREENWell, as head of the Planetary Science Division here at NASA, you know, my concern's always been about scientific discovery. And Mars has always been in our sights. Now how that connects of course to human exploration is really very simple, in that, human exploration is not like "Star Trek." It's not, "Go where no man has gone before," as they say. It's really all about the scientists being the pioneers, understanding the physical environment, understanding what resources are available, the hazards, and then be able to interact with human exploration on how they would leverage that knowledge for them to be able to go.

GREENAnd so, consequently, our plans have been to begin more -- a concerted effort to work with human exploration, now that we know a significant amount about Mars.

ROBERTSAnd of course you have competition. SpaceX, as Steve Petranek was talking about, the Elon Musk company, has been doing a lot of work in this. Are you cooperating with SpaceX? Do you have a relationship with them?

GREENYeah. It's really not -- I wouldn't say it's a competition at all. I mean, we really appreciate his vision, his thinking, his ability to build the commercial rockets that, indeed, NASA's purchasing for resupplying station and, you know, his long range vision of going to Mars. You know, we appreciate that greatly. And then of course, NASA is, indeed, developing capabilities where we're -- as already mentioned by Stephen -- developing the MOXIE instrument for our next rover that will launch in 2020 and begin to develop those instruments we call in-situ research -- resource utilization, ISRU, instruments that would then use that environment to create a resource for humans. And MOXIE is the first one.

ROBERTSAnd tell us about Orion. This is the rocket that NASA is developing. And does this have the capability now to reach Mars.

GREENYeah, of course, Orion is the capsule that sits on the rocket.

ROBERTSOkay.

GREENAnd the rocket is really called the SLS, the Space Launch System. This is, indeed, a very important transportation capability. We recognize that bases on Mars would have to have several tens of tons delivered to Mars and then be able to leverage and utilize that. And that's going to require some hefty push. So the SLS is, I think, on the order of maybe 5 to 10 percent more capable than the Saturn V. So it is, indeed, the next big step to be able to get a lot of material off this planet and in a push towards colonization of Mars.

ROBERTSNow, is colonization of Mars a official goal of NASA?

GREENIt is in the sense that it's really all about humans to Mars. I mean, our sights are not in the 100-year, 50- to 100-year timeframe that Elon is thinking -- and that's really exciting, I'm delighted as he comes out and talks about these things in important ways -- but it's really that first big step. It's really all about how would we accomplish getting humans to Mars, the kind of things that they would do. Now, the first, next connection that we're doing with human exploration from a scientific perspective is we've already announced to the science community that there are certain requirements for humans to have on Mars.

GREENAnd we want the science community, based on their in-depth knowledge of the planet, to be able to propose actually sites that humans could go to Mars. So at the end of October, we will have our first major international workshop where we talk about the top sites on Mars for humans that our scientists believe will have the capabilities, the abilities and the resources available to them.

ROBERTSI'm Steve Roberts and you're listening to "The Diane Rehm Show." Jim Green, from NASA, one more question. I really appreciate your spending some time with us. In his book, Steve Petranek, in quoting Elon Musk and others, predicts a mission to Mars 2027. Is that a realistic timeframe from NASA's point of view?

GREENIt's a little on the early side. We're actually, you know, Mars creates nice opportunities every 26 months. So we're looking more in the 2030s. But, you know, it's really pretty close.

ROBERTSThese opportunities mean -- excuse me, but I want our listeners to understand -- when you say these opportunities, meaning in terms of their orbit and their proximity to Earth?

GREENCorrect.

ROBERTSOkay. Go ahead.

ROBERTSYeah. Planetary science has, you know, has to follow Kepler's laws, you know. And that means, as things line up -- just like a passer in a football game throws, the quarterback throws the football, it's really going to a different place and the receiver receives it down field -- and we do that with Mars. So we'll launch at a particular time. And in about 180 days, we typically can get a mission to Mars. And then it's the landing or it's an orbiter or it's, you know, some aspect where then we use Mars' gravity to throw us out into the -- further out into the solar system, et cetera, et cetera.

ROBERTSRight.

GREENBut it's all about Kepler's laws.

ROBERTSOkay. Jim Green, he's director of NASA's Planetary Science Division. Thanks so much for joining us on "The Diane Rehm Show" this morning. We really appreciate it.

GREENMy pleasure.

ROBERTSOkay, sir. Steve Petranek, what's your reaction to what Mr. Green had to say?

PETRANEKWell, it's really interesting to hear NASA say that it has always had Mars in its sights. I think that's actually true but the sights that it's had have been for rovers. NASA has really evolved, over the last 40 years, a kind of, why-should-we-send-humans philosophy. And they have said, we can accomplish just as much with rovers as we can with humans. And that's a completely different philosophy from the one espoused by Elon Musk. They're just simply different points of view. I thought it was fascinating that Jim said that -- talked about MOXIE being available for humans.

PETRANEKMOXIE was developed to make oxygen for rocket fuel because oxygen -- liquid oxygen -- most rockets are powered by, or oxidized rather than powered -- but they use two fuels: hydrogen and liquid oxygen and liquid hydrogen, or they use -- they will start using liquid methane and liquid oxygen because that's a more efficient rocket. But NASA developed MOXIE to make oxygen on Mars, not for humans to breath but to propel its rockets so they could get back.

ROBERTSBut can it be applicable?

PETRANEKOh, it's very applicable to providing oxygen for humans. And when he talked about the SLS launch system for the Orion capsule, which could eventually get us to Mars -- or get NASA to Mars and he talked about that rocket being 5 to 10 percent stronger than...

ROBERTSSaturn.

PETRANEK...than the Saturn V, it's interesting that Elon Musk plan for the Mars colonizer rocket will be two times as powerful as the Saturn rocket. And Musk is going to use a very interesting philosophy that is derivative of what Wernher von Braun wanted to do.

ROBERTSSteve Petranek, his new book is, "How We'll Live on Mars." Also there's going to be a TED Talk associate with this book, right Steve? But I think that's going to be available in...

PETRANEKIn September.

ROBERTS...in September. Give us a call. We've got a couple lines open. We're going to go to your calls as soon as we come back. I'm Steve Roberts sitting in today for Diane. Steve Petranek and I will be here in just a minute.

ROBERTSWelcome back. I'm Steve Roberts, sitting in today for Diane. My guest this hour, Stephen Petranek well-known science journalist who has a new book out called "How We'll Live On Mars." And Stephen Petranek, a lot of our listeners have questions about that very topic. So let's start with Grace, who tweets, how many settlers would go to Mars in the initial colonization efforts?

PETRANEKThat's a good question. Probably the first landing on Mars will be somewhere between four and 10 people. Then there will be a period of supply ships that will go to Mars to establish the materials needed to set up a base, and in the early 2030s, probably the first big trip to Mars, at least from SpaceX's point of view, would probably be somewhere in the neighborhood of 100 ships, each carrying about 80 people, so maybe 8,000 people go on the first trip.

PETRANEKAnd then, as Jim Green (PH) explained, because of the alignment of the two planets, they -- Mars can be as much as 1,000 times farther away from Earth than the moon is. It took us three days to get to the moon. It takes a long time to get -- it takes eight months to get to Mars. So you don't make this trip casually, and you send all the rockets at once, and they would leave about every 26 months. So between 2030 and 2040, you'll have an opportunity for five major trips.

ROBERTSStanley emails, how does your guest to propose to carry enough food and water and repair and spare parts? There's no manufacturing base on Mars. You have to take things with you and be re-supplied from Earth.

PETRANEKEverything you take is extremely valuable. Mass and energy are great premiums for making a trip to Mars. He's absolutely right. So you don't take the water. You only take enough water to survive on the ship while you're going, and you recycle water. I mean, humans don't actually consume and eliminate that much water on a trip to Mars. You know, it passes through your body, and then you recapture it, and you reuse it. But Mars has lots and lots...

ROBERTSIs that technology already being used on the shuttle and the space stations?

PETRANEKThat technology is use on the space station. It's been used for decades, literally decades. It's completely established technology. As I continue to say, all the technology we need for getting to Mars and living on Mars we already have.

ROBERTSFacebook comment, I'll go, as long as I can still get Netflix. But who will go?

PETRANEKIt's -- Musk imagines that the people who go are basically people who are, say, in their mid-40s, and they're at some kind of turning point in their life. They have enough money to buy a ticket from him, which is going to cost a half-a-million dollars. You know, they sell their house, they pack everything up, they get in the -- they turn everything into cash, they buy the ticket, they get in the rocket ship, and they go, and they never come back.

ROBERTSAnd another email we get raises the question about health. Eugenics remains anathema in current thinking, yet will -- there will need to be some sort of selectivity in the population privileged to live in that brave new world? What do you think?

PETRANEKI think one of the prices you will pay by going to Mars is a shorter lifespan, and I think that will become obvious to people before they go, because of the radiation exposure that you'll endure both in the trip there and once living on Mars. Now the interesting thing about...

ROBERTSAnd this is a one-way ticket.

PETRANEKThis is a one-way ticket. And this is an interesting thing about how this radiation exposure works because there are people in our population who are not as affected by radiation as others. That's a genetic predisposition that is built into those people. So we are right on the verge now of being able to control our own evolution and our own genetics. We can actually edit the genes that are already in the human body. So if we can discover what the genetic predisposition is for the people who are more protected from radiation naturally, we may be able to replicate that in our bodies. So we may not have to choose people who do better under radiation exposure, we may simply be able to change ourselves or our offspring so that they're more adapted to life on Mars.

ROBERTSWell, there's another genetic dimension of this that you talk about in the book, which is, you know, people who -- where you can genetically change people to have more tolerance.

PETRANEKAbsolutely. I mean, we can edit the genes in your body right now, and we're getting better and better at that. We're just on the verge of that. You know, eventually, as people both adapt on Mars through accidental mutations in their genes through successive generations, or purposefully adapting people to live better on Mars, perhaps we can adapt people so they can breathe more than five percent of CO2 instead of passing out.

ROBERTSThat was the -- that was the alteration that I was -- you mentioned in the book.

PETRANEKI see no reason why we can't do that and why we can't do that in a relatively short period of time. So you may end up with a human being who lives on Mars who is of a different species than a human being who lives on Earth.

ROBERTSWoo-hoo. Let's turn to some of our callers. Let's go to Tony in Lancaster, Pennsylvania. Tony, welcome, you're on "The Diane Rehm Show." Tony? Don't see Tony. Okay, let's go to Tim in Raleigh, North Carolina. Tim, you're on the Diane Rehm Show.

TIMA couple of quick comments or questions, I'll try and make them brief. I'm a little bit concerned that NASA doesn't seem to be able to get people to the space station currently, and we have to rely on the Russians to do that, who have told us that they're not going to do that forever. And secondly, I know the moon isn't a final destination, but wouldn't it be a good training ground for building structures and going through the processes of trying to develop a organized community in a harsh environment?

ROBERTSThank you, Tim. We've had several questions about that, about the moon as a way station. Please answer Tim.

PETRANEKYeah, let me answer the moon thing first. The moon is a wasteland. It has no great value to us, and everything that we can learn by going to the moon and building a habitat there is something that we can actually learn on Earth and we can figure out on Earth. I really can't see much value in using the moon as a place to practice to go to Mars. I think we can figure out everything we need to figure out both by going to Mars and by practicing on Earth.

PETRANEKAnd, you know, this a philosophy that goes all the way back to Wernher von Braun, who actually didn't want to go to the moon in the 1960s. He wanted to go to Mars, and he said we have the technology to be able to go to Mars, and we should land on Mars first instead of the moon. Now, one of the interesting sidelights to this is that the Russians, who had a very well-developed space program in the early '60s, thought that they might leapfrog the United States, which had announced that it was going to the moon, and send a human being to Mars in the same timeframe that we were sending Apollo astronauts to the moon. And Khrushchev killed the plan and said I'd rather have more ICBMs than send somebody to Mars.

ROBERTSInteresting. Let's go to Kelly in Tampa, Florida. Kelly, you're on "The Diane Rehm Show."

KELLYHello?

ROBERTSYes, you're on the air. Please go ahead.

KELLYHi, I have a question about the MOXIE device, actually. The way it was described by your guest says that it's going to, you know, rip the oxygen molecules away from the carbon in the carbon dioxide. My question is, where would that excess carbon go?

PETRANEKIt would simply be basically a soot product that comes out of one end of the machine, and it's not that significant a problem to deal with. Pure carbon is not an environmental problem. Carbon combined with other things can be -- like oxygen can be an environmental, as CO2 is on Earth. The MOXIE machine is a very interesting, kind of reverse fuel cell that uses ceramics and a heck of a lot of energy to rip that carbon atom off. That's a very tight bond between carbon and oxygen.

PETRANEKAnd one of the problems in up-scaling the MOXIE machine, which is designed from the get-go to be able to be built 100 times larger and provide 100 times more oxygen than the initial machine will be that will go to Mars in 2020, one of the problems is that it requires a lot of energy to do this. And it will require a small nuclear reactor or one heck of a solar field to pull this off.

ROBERTSLet's turn to Marie in North Smithfield, Rhode Island. Marie, welcome, you're on "The Diane Rehm Show."

MARIEHi, thank you. I wonder if Mr. Petranek has thought about or commented on, or whether he has heard Elon Musk comment on, the moral implications of colonizing another planet. I mean, we have pretty clear hindsight now on the ramifications of colonization in the human past, and I wonder what his thoughts are about our ethical and moral obligations as deeply self-aware creatures thinking about further colonization in the future and whether we're planetary parasites. Thank you.

ROBERTSThank you, Marie.

PETRANEKI think this is a very serious question and one that comes up from time to time, and one of the points of this book is to let people know how quickly things are developing and how soon people will actually be on Mars so that these kind of issues can be discussed. But when European settlers came to the Americas, there were other people living here who occupied the land, and they were displaced or killed or made very sick by the Europeans' illnesses, and that was a horrible thing that occurred, that kind of colonization. The kind of colonization that Britain imposed on India was a terrible thing.

PETRANEKThere are no people on Mars. So there -- and as far as we know, there's nothing alive on Mars. So whether or not we're going to contaminate this planet or not is another serious question, with our different life forms, and in order for us to live on that planet, we have to seriously change it. We have to terraform it, we have to make it warmer, we have to change its atmosphere, we have to find a way to bring water to the surface and make it instead of being ice all the time being water.

PETRANEKSo there are a lot of things we're going to do to this planet in order for humans to live on it, and that's a fair discussion to have. But the one thing I would like to point out is that colonization is a dirty word because it is a dirty word in our culture because of the implications of what it does to other human beings, and there are no other human beings on Mars.

ROBERTSBut there is the environment.

PETRANEKAbsolutely.

ROBERTSAnd you've used this word terraform. Please define it and explain how that fits into some of the planning because it's a very important part of this.

PETRANEKIt's going to be very uncomfortable and very hostile to live on Mars as we find it. So the people who live there, especially if there are a lot of people living there, the first thing they're going to want to do is change the planet to make it easier to live there. The first thing you would do, and this is very synergistic, is warm the planet. And the way you do that is -- there are several ways of accomplishing this. I'll just talk about one. One is to have a giant solar mirror, which is basically a very light, light sheet of plastic that's sprayed with an aluminum film, and it works as a mirror, and you put it up in orbit around Mars so that it focuses the sun's light on the south polar region of Mars, where there's a great deal of frozen carbon dioxide.

PETRANEKAlmost immediately the frozen carbon dioxide will sublimate to become gaseous carbon dioxide instead of frozen, and as we know on Earth, carbon dioxide is one heck of a greenhouse gas, and the sun's energy will suddenly tart being captured within the atmosphere of Mars and on the surface. So Mars will heat up by 20 or 30 degrees in a very short of period of time. We should actually be able to get the surface temperature of Mars up from an average of minus 80 to an average of about 20 degrees with some of these techniques. Once you have...

ROBERTSSo this is deliberate global warming?

PETRANEKThis is deliberate global warming, and we might even create manufacturing plants that make chlorofluorocarbons, those things that we used to have in our refrigerators and in spray cans that we've outlawed on Earth, because if we spew a lot of those into the atmosphere, it will also make the planet warm up. And a warmer planet, all of a sudden you get water flowing. You get water flowing, all of a sudden you can start planting plants, and plants make oxygen. So this is all incredibly synergistic. And...

ROBERTSA virtuous circle.

PETRANEKWhether -- well, I don't know if it's virtuous. But whether or not you -- it partly depends on whether or not you consider this like a wonderful wilderness, and you don't want to change it, or you're going to change it.

ROBERTSI'm Steve Roberts, and you're listening to the Diane Rehm Show. You mentioned also in the book potential economic implications, apart from the fantasy of a reality TV show. But there are, among the first colony, the history of colonization often involves extractive industries. It involves logging, mining, and you talk about that as a potential economic basis for a Martian colony.

PETRANEKWell, one of the economic advantages of being on Mars is you're suddenly very close to the asteroid belt between Mars and Jupiter, in which there are over 700,000 countable asteroids. Most of those asteroids are made out of heavy metals like platinum and gold and iron, and they are very easily and readily minable, and in fact there are two corporations in the United States that have already started, including one that has investment money from Eric Schmidt, the chairman of Google, and Larry Page, the CEO, to mine asteroids.

PETRANEKAnd it will be a lot easier to mine asteroids from Mars first of all because you're closer to them and secondly because Mars' gravity is only 38 percent that of Earth. So it's going to be a lot easier to launch a rocket to the asteroids and mine them. There may be heavy metals in former streams on Mars. There may -- you know, it's conceivable there could be a gold rush or something like that, but most of the Martian economy will revolve around simply the people there.

PETRANEKSomebody will make a Pizza Hut and, you know, somebody will start an iron factory, and most of what happens on Mars will be a self-contained, self-sustaining economy, just as most of the early Americas were self-sustaining colonies.

ROBERTSAnd we do have an email that asks the question, who will own the land and resources on Mars, individuals like Elon Musk, companies like SpaceX, countries like the U.S. and China? Brian asks this.

PETRANEKThis is one of the really tough questions that needs to be answered before we launch the first rockets to Mars because there's a 1967 space treaty that more than 100 countries have signed, including all the major countries that have space programs, and that treaty says a bunch of different things. One of the things it says is that you can't put nuclear weapons in space.

PETRANEKBut one of the other thing it says is that nobody owns anything outside of the Earth. So the Americans were the first ones to get to the moon, but we don't own it. We own the stuff we left there, but we don't own the moon. And there's another part of the treaty that's really interesting, which says that we are responsible for any damage we do if we land on an asteroid or on the moon or on Mars. So there is technically no ownership of Mars. It should be treated, probably, the way we treat Antarctica, as a cooperative, explorative, exploitative area. But no -- technically under this 1967 treaty, no one can own land there.

ROBERTSFinal, quick question, and you talk a lot in the book about what we might learn about ourselves by colonizing space. How would you sum up the potential lessons here?

PETRANEKWell, one of the things that we know from people that have been sent into space is they look back at Earth, and they see this very fragile blue ball, and it's surrounded by an extremely thin little layer of blue stuff. That blue stuff is our atmosphere. It is only one mile deep. We learn to respect the Earth by learning how hard it is to live on Mars.

ROBERTSStephen Petranek. His book is "How We'll Live On Mars." Thank you so much for being with us. I'm Steve Roberts, sitting in today for Diane Rehm. Thanks for spending an hour of your morning with us.