Planetary Radio: Space Exploration, Astronomy and Science - Journey to the Center of the Earth!

Episode Date: May 19, 2003

Journey to the Center of the Earth!Learn more about your ad choices. Visit megaphone.fm/adchoicesSee omnystudio.com/listener for privacy information.See omnystudio.com/listener for privacy information.

This is Planetary Radio. Hi everyone, I'm Matt Kaplan. Jules Verne wrote about it. A recent movie also sent people there. But in reality, our own planet's interior remains mysterious. Our guest today knows as much as anyone about the Earth's core, and he'd like to know more. David Stevenson has even come up with a thought-provoking way to get there. Later, Bruce Betts will drop in with the new trivia contest.

First, though, Emily wonders if bits of Earth have traveled anywhere else in the solar system. Stick around as we get to the core of the matter in this week's Planetary Radio. Hi, I'm Emily Lakdawalla with questions and answers. A listener asked, What are the odds that we will find Earth rocks on the Moon, just like we have found Moon and Mars rocks on the Earth? Finding an Earth rock on the Moon is possible, but very unlikely, even for an expert looking for such a rock. To understand why, first you have to know how we find meteorites on the Earth.

There are about 5,000 known meteorites, of which about 50 are believed to have come from Mars or the Moon. Meteorites are collected in the highest abundances in places where solid stones are very unusual, like farmland in Kansas and Nebraska, or blue ice fields in Antarctica. Because stones are so rare in these environments, any stone that is found has a high likelihood of being a meteorite. Unfortunately, the moon probably has no such stone-free regions, so meteorite hunters there would have to examine literally millions of rocks before they had

a reasonable probability of turning up a meteorite. Out of all the lunar samples of rocks and soil, only one millimeter-sized chip was found to have come from a meteorite. To learn more about finding Earth rocks on the Moon, stay tuned to Planetary Radio. David Stevenson is the George Van Austel Professor of Planetary Science at the California Institute of Technology, better known as Caltech. He spends a great deal of time thinking and looking into, to the degree that you can look into it, what is under our feet. That is, what are planetary bodies made of? And it is an area about which we know surprisingly little,

although recent developments have helped us to learn quite a bit more. And that's what we'll talk about today, as well as, Dr. Stevenson, I hope, a modest proposal that you have recently made and was just published in Nature. Welcome to Planetary Radio. Good to be with you. Do you ever wish, as someone who studies planetary science, and particularly planetary interiors, that NASA would, along with follow the water now and then, say, follow the magma?

Yes, indeed I do. I wish, first of all, that whenever we want to understand something, that we think about how to actually be there and not just measure things from afar. One of the remarkable things about space exploration has been the extraordinary amount of information we have gained about other planets by going there. we have gained about other planets by going there. You can look through a telescope at a planet, learn something about the planet, but you learn so much more when you go there. In the same way, I would like to think that we would be surprised and would gain immensely if we could go to Earth's core

or if we could go subsurface on other planets. You have actually made this modest proposal, and we should say that on your website, you admit that it's a bit tongue-in-cheek, but a proposal that could actually take us deep under the crust of the Earth in the space of about a week. Yes, indeed. of the Earth in the space of about a week. Yes, indeed. My idea is that you start a crack at the Earth's surface, a fairly modest crack by the scale of what the Earth does naturally all the time, but a special kind of crack because it would

be filled with liquid iron. Liquid iron is much heavier, much more dense than the surrounding rock, and the force, the gravitational force, because of that heavy material, will force open the crack at the bottom of the crack, and so the tip will go down into the earth and will keep going down, and if it works right, it will go all the way to the core in about a week. I read this paper, which was printed in the May 15 issue of Nature. While it is tongue-in-cheek to a degree, you also imply, or maybe you state overtly, that while there would certainly be technological challenges to get over in achieving this kind of a mission,

that it is conceivably possible with known science and known technology? I think the crack itself is possible. There are some significant scientific questions about what actually happens. You could imagine some ways in which the crack would fail to go all the way, and that's a concern. But that part of it has a fairly sound scientific basis because it is something that we know the Earth does already, admittedly over a shorter distance, typically 100 kilometers with molten rock coming up beneath volcanoes. The much more difficult part, the part that could well prove impossible, is to insert

a probe, a small solid body the size of a grapefruit or a basketball, into the liquid iron in this crack and have that probe measure something useful and send that information back. Sending the information back, I think, can be done. Actually measuring something useful, I admit, is a really major challenge, and I'm not sure at this point how to accomplish that. I should ask on my own part and on behalf of other laypeople, my own part and on behalf of other laypeople, how in the world could a probe with functioning instruments survive existing for a week in molten iron? Well, there are two aspects to that.

First, the basic chemistry of it is okay. That is, you can find a composition of a liquid that is mostly iron so that you can find a composition of a liquid that is mostly iron so that you can have a solid in it that survives despite the high temperatures. It's actually not really that much different from having an iceberg sit in salty water. You can arrange the temperature so that the ice is not melting under those conditions. And likewise, if you have a liquid iron alloy, for example, the temperature so that the ice is not melting under those conditions. And likewise, if you have a liquid iron alloy, for example, it might have a lot of sulfur in it so that it doesn't have a tendency to freeze. And you could place another iron-dominated chunk of solid material that would float along

with it and would have no tendency to dissolve. The more difficult question is putting into that probe instruments that work at very high temperature. The electronics that we are familiar with in everyday life, the electronics in our computers, cannot survive at those high temperatures because they're based on silicon, and silicon won't work at very high temperatures. Computers in general fail to work if you heat them up. But you can find other materials, and the best candidate material is diamond. Diamond is solid at these extreme temperatures and pressures. In fact, diamonds naturally exist inside the Earth at these conditions.

And diamond is a semiconductor, just like silicon at room temperature, so you can make electronic circuits out of diamond. Has any company or any university ever actually created a circuit using diamond semiconductors? This is new to me. As far as I know, it has not been done. It has been talked about casually, but there has been no incentive. One of the points of writing this paper is that people haven't considered this idea seriously because the incentive has not been there.

And I believe that this is a failure in the way we fund and think about science, that there's a tendency for us to spend our time doing things where we know that the resources exist to do what we want to do, and we don't spend enough time providing enough resources for thinking about things that are a little bit out of the ordinary. Diamond has certainly been suggested in connection with making instruments

that survive on the surface of Venus. Venus has a surface that's much hotter than the surface of the Earth. It's not as hot as the inside of the Earth, but it's still hot enough that conventional electronics would not work. So if you wanted to have a seismometer working on Venus for a long time, you might indeed use diamond there too. So you were obviously thinking on a number of levels when you wrote your A Modest Proposal. I should say the full title of David Stevenson's paper just published in Nature is A Modest Proposal, Mission to Earth's Core. You were paying, I think, tribute to an Englishman of note of some hundreds of years back.

Jonathan Swift was, in the minds of some people, one of the greatest exponents in the use of the English language, better known for his essays than for longer pieces of work, although he's famous for that too. And he wrote an outrageous and extremely provocative essay entitled A Modest Proposal, in which he sought to solve the Irish problem, which at that time was a lack of food. And he suggested that one way to solve the problem was for people to eat their children.

And of course, he didn't mean this seriously, but he was making a serious point about the nature of the problem that had to be solved. I picked that up as somewhat exaggerated, but nonetheless similar idea of outrageousness in the case of my own idea. As in our own time, some works of satire are not always taken as such. Unfortunately not. Dr. David Stevenson is our guest. We're going to take a break, but then if we can, Dr. Stevenson,

if we can come back and talk a little bit about what we do know about planetary interiors, and I know you include in that moons and other planetary bodies in our solar system, and I assume by extension beyond. Planetary Radio is the program that you're listening to, and we will be back in just a minute. This is Buzz Aldrin. When I walked on the moon, I knew it was just the beginning of humankind's great adventure in the solar system. That's why I'm a member of the Planetary Society, the world's largest space interest group.

The Planetary Society is helping to explore Mars. We're tracking near-Earth asteroids and comets. We sponsor the search for life on other worlds. And we're building the first-ever solar sail. You can learn about these adventures and exciting new discoveries from space exploration in The Planetary Report. The Planetary Report is the Society's full-color magazine. It's just one of many member benefits. You can learn more by calling 1-877-PLANETS.

That's toll-free, 1-877-752-6387. And you can catch up on space exploration news and developments at our exciting and informative website, planetarysociety.org. The Planetary Society, exploring new worlds. Matt Kaplan back with Planetary Radio and our special guest today is Professor David Stevenson. He is the George Van Osdall

Professor of Planetary Science at Caltech. We were in the first half of our conversation talking about his modest proposal, a mission to Earth's core, which you can find we should probably say, Dr. Stevenson, on your website. And we will give that URL if you don't mind at should probably say, Dr. Stevenson, on your website. And we will give that URL, if you don't mind, at the end of the interview.

That's fine. Let's talk a little bit about what we do know, even without your, shall we say, novel probe. And how have we learned what we know about the interior of the Earth? Has our exploration of the solar system helped us to learn more about the Earth's own interior? I would say first that in the case of the Earth, most of our information about the deep interior is from seismology, from waves that are produced in earthquakes. From this, we have learned about the liquid character of the outer core of the Earth

and something about the composition of the Earth and its layers. With other planets, we have, for the most part, not been able to do seismology, but we have learned a lot from using gravity and altimetry. In the case of solid bodies such as the Moon and Mars, a tremendous amount has been learned in the last 10 years by looking at the shape of the planet, by looking at how it rotates, and by looking at the gravity field.

Recently, for example, it has been determined that the core of Mars is liquid like the core of the Earth. Another area where we have learned a great deal is with magnetic fields. Magnetic fields are often produced deep inside a planet in the core, but in some cases are also affected by near-surface environments. I was involved some years ago in the discovery of an unusual magnetic field near the moon of Jupiter called Europa, and from that we decided that Europa has a water ocean. There is now a great deal of interest in water oceans elsewhere in the solar system other than the Earth.

These are oceans that are beneath the surface, so you don't see them directly, but they're one of the most exciting examples of what you can learn about interiors of bodies by looking at the fields, the gravity, magnetic field, and so forth. While we're on the subject of Jovian moons, you are involved with at least a proposed mission to reach some of those moons, or the so-called icy moons? Yes, indeed. There is now within NASA an initiative, a nuclear science initiative,

a program called Prometheus, which is funded, so it is actually happening, even though the first spacecraft in the series is many years off still. in the series is many years off still, but the first mission in this program is JIMO, J-I-M-O, which stands for Jupiter Icy Moons Orbiter, and this is a nuclear-powered spacecraft. By that, we mean that there is a nuclear reactor that puts out about 500 kilowatts of electrical power. The electrical power is then used to drive an ion motor of the same kind that was on Deep Space One. So that part is actually not new. And for that matter, we've had nuclear reactors in space before also, although on a small scale and not into deep space.

But this is an astonishing mission if it happens. Tentatively scheduled for launch in 2011, it will go out rather slowly, I might say, to Jupiter. But once it gets to Jupiter, the ion motor gives you the ability to go into orbit successively around Callisto, Ganymede, and Europa and spend time in orbit around each of these satellites, something that is unimaginable with the current technology that relies so heavily on ballistics.

So this is a very exciting mission. Yeah, very exciting and extremely ambitious. And what a wonderful testbed for this new means of propulsion, at least new in that it would have so much electricity to run that ion engine, thanks to the nuclear reactor rather than solar power or the older RTG generators that are still used on many spacecraft that get too far from the sun for solar cells. Yes, indeed. on many spacecraft that get too far from the sun for solar cells.

Yes, indeed. I wonder if we could bring it back home to Earth and talk about how our image, our concept of the Earth's interior has changed, as we have learned from these tools, which are, I suppose, somewhat indirect, seismic, magnetic field monitoring. somewhat indirect seismic magnetic field monitoring. Has our view of the Earth's interior changed a great deal even in recent years? It has changed quite a lot. We have known for quite some time that the very central part of the Earth is a solid, solid iron.

We have found from seismology in recent years possible evidence that that part of the Earth is rotating at a different rate from the Earth's surface. This is controversial. It was put forward. There were data to support this idea. In the last couple of years, people are backing away a bit and expressing doubt about whether this is really true, but that's the normal scientific process, and it's a very exciting thing. For me, one of the most interesting things that has happened in the last two or three years is a revival of an old idea that was not taken seriously for many years,

and that is that the Earth's core may have radioactive heat sources in it. and that is that the Earth's core may have radioactive heat sources in it. It turns out that the energy requirements for our magnetic field, which is generated in the core, are leading people to suspect that you need more energy down there than we previously thought was available just by having the Earth cool off from a hot state. And indeed, the mission that I proposed to the Earth's core ever to take place, one of the most interesting and important things it would attempt to find out

is whether there are additional heat sources down there. The best candidate is potassium-40, which is a radioisotope of potassium, and could in principle release a significant amount of heat if there were potassium dissolved in the iron in the core. Dr. Stevenson, we only have a couple of minutes left. I want to give you the chance to make one more impassioned plea, if you choose, for this exploration of what is under our feet. You make the point in your paper in the May 15 Nature. I don't know if

you've stated it exactly this way, but we know more about the, proportionately speaking, 10 to the 57th above our heads than we do the few thousand kilometers under our feet. I think that's true in the sense that the space above us is more transparent. Of course, we are beings that depend a lot on visible light and electromagnetic radiation. That kind of information is simply unavailable for us beneath our feet. And in that sense, the inside of the Earth, the part of the universe beneath us, is more mysterious. the part of the universe beneath us is more mysterious, and I think it is an exciting area to visit to know more about, in significant part because we live on the Earth and we should have this curiosity about the planet that we live on.

Forgive me for asking a somewhat flippant question, at least I think it is. The movie The Core came and went rather quickly. I did not catch it. Did you see it? I have to admit that I did not see the movie. I was given the opportunity to see it, even for free, but the opportunity passed quickly. I should explain that my paper in Nature was triggered by the movie. There is no scientific connection between the movie and my paper. However, I was asked back in October and November

by someone who, in some sense, was working for Paramount to offer scientific commentary on aspects of the movie. And at that point, ideas that had been in my head for 10 years, I decided that those ideas should be put in writing. And so I sat down and actually wrote my paper, triggered by knowing that the movie was going to come out. Well, it's good to hear that science still follows art now and then. Our guest has been Dr. David J. Stevenson. He is the George Van Austel Professor of Planetary Science at Caltech, the

California Institute of Technology. I said that we would give your homepage. It is www.gps.caltech.edu dot Caltech that's one word dot edu slash faculty slash Stevenson with a V dash excuse me slash Stevenson dot html and Dr. Stevenson

I should say that for anyone who missed that which was probably most normal people it will also be on our website where this radio program is posted

and I want to finish really just by saying thank you. It has been such a pleasure to talk to you. We spend so much time about talking about what is in the heavens on this program. It's very good to talk a little bit about terra firma. Thanks for the opportunity. Dr. David Stevenson of Caltech.

Planetary Radio will continue in just a minute. Transcription by CastingWords moon? It's pretty unlikely. The moon doesn't do as good a job of preserving small meteorites as the Earth does because of its lack of atmosphere. The Earth's atmosphere slows down incoming meteorites with diameters smaller than a few tens of meters and drops the stones relatively gently onto the surface, where they can be collected more or less intact. But there's no atmosphere on the moon, so meteorites hard land on the Moon's surface at speeds of a few kilometers per second and are mostly melted and vaporized on impact. But all of this isn't to say that it's impossible to find Earth fragments on the Moon. The best strategy for finding Earth rocks on the Moon would be to look at the ejecta deposits near small craters,

searching for fragments of the incoming meteoroid. If the occurrence of Earth rocks on the Moon is similar to that of Mars rocks on the Earth, you would have to examine about 300 craters and succeed in finding identifiable fragments of the meteoroid before there was a reasonable chance of finding one made by an Earth rock. Got a question about the universe? Send it to us at planetaryradio at planetary dot org. Be sure to provide your name and how to pronounce it and tell us where you're from.

And now, here's Matt with more Planetary Radio. For the first time ever, What's Up? has gone on location. We are at beautiful Descanso Gardens. And Bruce, welcome. Thank you very much. I'm excited to be botanical today. And we should say this is quite a beautiful place and we're not far from Planetary Society headquarters. And I don't know why we're here, but it's a beautiful place to be. There is a reason, but apparently we won't be telling you. No, we don't have time. Bruce, what's up? Well, we've got planets, planets, planets, and planets.

Hopefully many of you saw the total lunar eclipse last week. It was spectacular. Yay. We've got in the evening Saturn getting pretty low in the west just before sunset. Jupiter extremely bright in the sky in the evening. Brightest object up there in the early morning right before dawn. Venus in the evening, brightest object up there. In the early morning, right before dawn, Venus in the east, extremely bright. And Mars getting quite bright, very bright now,

and getting brighter and brighter as we move towards the opposition in August. And you can see that looking orangish-reddish as you look towards the southeast, south-southeast before dawn. Do stay tuned to Planetary Radio over the next few weeks, and check out the Planetary Society website. We're going to have lots more stuff having to do with Mars as we reach this historic, close pass to the red planet. Indeed, an historic pass.

An historic. Within 70, I wasn't correcting, within 70. I just wanted to sound impressive, but now I don't, so what a bummer. Closest it'll be within 73,000 years since it's been this close. It will be August 27th coming up. It's also why there are five spacecraft going to Mars at this time, because it's coming close. We can shoot those suckers out there fairly easily. It's going to be a great year and a little bit more for Mars.

Let's move on. How about this week in space history? Well, on March 23rd of 1965, Gemini 3, the first two-man American space mission, was launched. Oh, excellent. And that was a milestone because Gemini was another major step on the way to the moon. It was indeed. Well, you know what's next. I do indeed.

Hey, wait a second. Gemini, first two-man mission, twins, two. Wow, that's kind of cool. That's kind of neat. Anyway, sorry. Random space fact! Jupiter's magnetosphere is the largest single structure inside the solar system. If you could see it with your eyes, it would appear larger than our full moon.

Wow. Yeah. And that's the view that I want than our full moon. Wow. Yeah. And that's the view that I want, too, someday. As do I. Trivia contest. Shall we move to the trivia contest? Did I say we're at beautiful Descanso Gardens? It's lovely.

Yes, let's move on to the trivia contest. Last week's contest. Last week. Gusev. Who the heck was this person they named a crater after him on mars and the mars exploration rovers one of those missions is targeted to goosef crater who was this person well we had a lot of people who got the answer right should i go ahead and give the correct answer and our winner or do you want to tell people what who goosef was all right

i will it turns out it actually was not a character, a recurring character on I Spy. It was, however, a Russian astronomer, M.M. Gusev, lived from 1826 to 1866. Here is our winner, Joyce

Begoyen. Joyce Begoyen of Taylor, Michigan, was one of those with the correct answer, and her entry was randomly chosen from all of those correct answers. Joyce, congratulations. You're going to be getting the Mars 3-D T-shirt, which I don't think we've said yet. A 3-D T-shirt? That would be a good trick.

Coming soon, the Mars 3-D T-shirt. For now, you'll get a Mars 3-D poster, complete with 3-D glasses to allow you to see in 3-D. I'm sorry. We've given away so many t-shirt. For now, you'll get a Mars 3D poster complete with 3D glasses to allow you to see in 3D. I'm sorry. We've given away so many t-shirts. I mean, some t-shirts are 3D. But this is the Mars Pathfinder landing site in 3D. And it's the glasses that are really cool. I mean, that's what, you know, free 3D glasses.

I want to get some 2D glasses sometime. What is that? You just get like the red lens? We're not giving you the blue one, just the red one. Let's go on to next week's or this week's trivia question. This week's trivia question. Who is the first person to travel in space twice? And we mean literally, not figuratively.

Who is the first person to travel in space twice? What would figuratively be? Well, there are various people who seem to travel in space quite frequently, in a figurative kind of a sense. Kind of like us when we're at Descanso Gardens. Okay, first person to make a second trip into Earth orbit at least, right? That would be another way to phrase it. Well, actually, I'm just saying space.

Or beyond. No, we're just talking space. Just talking space. We're just talking space. Second person, travel to space. Okay, we're just talking space. Just talking space. We're just talking space. Second person, travel to space. Okay, this is a good one. This may be a little bit more difficult for people to look up. Go to planetary.org to enter.

You'll find all the instructions there. You do need to get that entry into us by Thursday at noon, this coming Thursday. Thursday at noon. That would be noon Pacific Daylight Time. Correct. And then we will, once again, choose from all of the correct answers, and you might be the next one to get what would it be. If it's not a 3-D T-shirt, it would be an extra large poster.

Send us the size of poster you'd like, and it really won't matter, but it will amuse us. I think we're done. That's just about it for this week, Bruce. I think we're done. That's just about it for this week, Bruce. Well, look up in the night sky and ponder looking at things in 3-D when lying back in a botanical garden. Thank you, and good night. From Descanso Gardens near the Pasadena headquarters of the Planetary Society, we've been doing What's Up with Bruce Betts,

the Director of Projects for the Planetary Society. Planetary Radio will be back next week at 5.30 p.m. Pacific on KUCI and KUCI.org, along with the Planetary Society website, planetary.org. On behalf of Emily and Bruce, Charlene Anderson, Monica Lopez, and Jennifer Vaughn,

thanks for listening.