NOVA; To the Moon; Interview with William K. Hartmann, Senior Scientist Emeritus at the Planetary Science Institute, part 1 of 3

Just tell me how, how was the moon form? We see it up there. Where did it come from? One moment, one moment. Ray about another inch higher. Right there. Okay, Rush. So, how was the moon? The current idea on how the moon was formed is that a large body in the early solar system, and this could be something as big as Mars, came in and hit the Earth and blew material out of the outer part of the Earth, and some of that material went into orbit around the Earth and then formed into the moon. What do we call that? People are calling that idea the giant impact hypothesis for forming the moon. Telling there.

We'll hire with the mic, Ray. One moment. Okay. The giant impact. When did this occur? The planets all formed about 4.55 billion years ago, that's 4,550 million years ago, and the impact that formed the moon apparently was in the first 10 or 20 million years after that, or maybe 30 or 40 million years after that. It's tens of millions of years after the beginning of the solar system. You want a shorter version of that answer? No, but in terms of the age of the solar system, that sounds quite good. All of these events were at the very beginning of the solar system, where again, if you think of 4,500 million year units, all of these are way back at the beginning. It's the first few tens of millions of years, and there were large objects,

asteroid-sized objects forming and moving around the sun and colliding with the planets. That's what the planets grew from. That's what planets were made from. Some of these objects got very big before they hit the planets. They themselves were growing. Within the first few tens of millions of years, within the first percent of the history of the Earth, the first few pages of the Earth's biography, these big objects were still colliding with the Earth, and one of them was big enough to blow this material out and leave some material stranded in orbit to make a moon for the Earth. Do you have one of those handy sort of analogies that the Earth was 100 days or 100 years old? This is all happening in the first few hours, few days? It's something like that. It's strange the time scale of the history of the Earth because so much happened in the first percent of the time.

Then, conversely, at the other end of the time scale, here we are mammals and human beings. If you compress the history of the Earth down to one day, civilization is like the flash of a flash bulb right before midnight. We're just talking about the last few seconds. We walk around in our daily lives with a completely wrong view of this. We tend to think of humans and dinosaurs going way, way back into the history of the Earth. The dinosaurs themselves are only representing the last percent of the history of the Earth, something like that. There's this vast time in the middle where the planet was evolving slowly and the continents were shaping up and life was evolving. If a spaceship came from an alien civilization and visited the Earth in the middle of its history, say, three billion years ago, it would have found a planet very different than the Earth today. It's really amazing to think about that. No life visible on the continents, no plants on the continents, no animals on the continents, an atmosphere which was different composition than today, mostly CO2.

It was a different planet. And the environment that we live in today has been shaped by the process of life, the plants releasing oxygen, the plants getting out of the ocean and colonizing the land, and so forth. So visiting the moon, having Apollo astronauts bring rocks back from the moon, gave us a window into the first third of the history of the Earth Moon system and particularly the events of the first few percent of the Earth Moon system. All those early events having been wiped out on the Earth by very complicated geology plate tectonics and volcanoes burying things and rivers eroding the surface away. But the moon still has a record of those very early events and that's one of the exciting things about having explored the moon is that we began to see what was going on in the early history of our whole Earth Moon system. Really lunar exploration has given us a picture of, we live in a system,

an Earth Moon system, it isn't just the Earth, it's the Earth and the moon together and the history of those two bodies is intimately connected. And we're beginning to see that now. Great. Can you give me just one more time, you had that flashball at the end of it? Yeah, let me think about that. Okay, great. All right, so in a 24-hour day, the origin of the moon, when is the moon created? Yeah, if you picture the whole history of the Earth in a 24-hour day, we're talking about the events of the first few tens of millions of years in the solar system. And that represents something like 10 or 15 minutes in the first history of the Earth. So we're talking about the events of the first 10 or 15 minutes and to put that in perspective, dinosaurs have been around for the last 10 or 15 minutes out of that 24-hour day and humans have only been around for the last few seconds or civilization for the last few seconds.

So the things that occupies as we think about the history of the Earth or the Earthman system tend to be the few percent of time at the beginning and the few percent of time at the end. And we have to remember there was a huge stretch of time in the middle there. Great. Okay, the last Apollo mission left the moon in 72. Now, as I understand it, you came up with this origin idea in 84. 74. 74. 74. 84 was the Kona conference in Hawaii and that was like 10 years after we had published the paper. We gave the first paper on this in the summer of 74 at a conference and then published our paper in 75. And then Al Cameron and Bill Ward also turned out independently to be working on this and published a paper in 76 or an abstract. So the first couple of papers were 74, 75, 76. And then those papers were sort of in limbo for 10 years.

And finally in 84 we, a group of us thought, well, it's been 10 years since the end of the Apollo missions more than 10 years. It's time to have a conference. What did we learn from going to the moon about the history of the Earth and the moon? And this conference which has become quite a well-known conference now was held in Kona, Hawaii in 84. And the existence of the conference, this is how science works. The existence of the conference spurred a lot of people to really start thinking critically about, let's go to this conference and hear about this. What do I have to say about this subject? And people came to this conference having really thought about all the lunar data that had been brought back from the moon. And lo and behold, what emerged at the end of the conference was that the idea of a giant impact was suddenly the leading hypothesis for how the moon might have been formed. All right, take me back though.

To 72, the last flight leaves the moon 74, you write your paper or publish your paper. What's the climate in the field in 74? How was that we see? The last flights left the moon in 72. And people had been digesting data from the rocks of the moon since the first landing in 69. Now, you have to put that period in perspective in terms of what was going on in understanding planet formation at the same time. So you have one stream of information as the actual geological rock data from the moon. You have another stream of information which has to do with how people thought the formation of the early solar system was proceeding. Back in the 60s, Cold War period, behind the Iron Curtain, here were some Russians, a school of Russians, studying these problems of solar system formation, particularly a man named Victor Sofranoff.

And they had published papers in Soviet journals not too well known in the west during the 60s about the aggregation process. The Russians particularly had recognized correctly, we would now say, that the early solar system involved countless billions and billions of particles, rocky grains, dust, and debris going around the sun. And these were hitting each other in aggregating. And Sofranoff worked out the mathematical theory of that. I had been looking at those papers to some degree. And as I say, sort of obscure Soviet journals that were being translated in obscure translations, they didn't really hit the west until, again, a somewhat obscure translation was done in Jerusalem. Here's another Cold War story, with funds that came from some agency in the US government to an Israeli program to translate Soviet literature, comes out, little gray paper bound book, still have it, of Sofranoff's work.

And this went along with a lot of work that I had been doing since my dissertation in the 60s on the cratering of the moon. And the fact that there clearly were some big impacts that formed 1,000 mile wide basins on the moon. So you have 1972, 73, 74, Sofranoff's work, aggregation, not only the earth was growing, but other bodies trying to also turn into the earth at the same time, and are these going to collide with each other? What's going to happen? Meanwhile, I'm looking at my crater data. I know that there's big impacts on the moon. Meaning that there's a big impact on the moon. And that's what I'm looking at. And I'm looking at some of the things that I'm looking at. And I'm looking at some of the things that I'm looking at. The impacts on the moon.

Meanwhile, rocks are coming back from the moon that indicate that the chemistry of the moon material is very similar to the chemical of the mantle of the earth. I'm going to stop you there because we need to be changed. That's Rule 2 or 3 coming up? No, that's not a bit like that. Just a couple of wild, I mean, this is MOS and wild shots, wild soundtakes, I'm sorry, wild soundtakes, atmosphere of the room. The tails, that's a tails atmosphere.

Okay, that was atmosphere number two. About a minute's worth.

High angle pan left to right with camera and then back left slightly. That was sink.

It was a tilt up and then pan. That's the slate, do you have the bright light on now?