Yvonne: And we're really interested in learning about the origin of life, so today we're here to talk to you about a few things that involve that study. We'll talk about spectroscopy, which is the study of light, habitable zones, which are the locations where planets around stars are best suited for life to develop, and we'll talk a little bit about the missions that astronomers are interested in in order to search for the origin of life. This field, by the way, is called astrobiology.

So, you may have a lot of questions today, terms that are new to you that come up. Please send in your questions by email; we're happy to answer them.

We'd like to start by talking about what is a star? A star is a great big ball of gas that's very hot, and inside it the temperatures and pressures allow the chemicals to be processed and turned into other things. We use spectroscopy to study what those chemicals are and the conditions of the star.

Michael: The light that comes from the star contains lots of information that we can decode. The technique that we use to decode the light is very similar to what you do if you've every used a prism, shown light through prism, and seen the rainbow of colors that emerge from the other side of the prism. In spectroscopy we do exactly the same thing. We collect light from a star, it's passed through a device called the spectrograph, which is just like the prism, and the light from the star is broken up into its various colors.

Yvonne: OK. So here is an example where you can see just what Mike was talking about. You have light coming from a star, and it's going through the prism, and it's breaking it up into the various different colors that we see. That rainbow spectrum is the background that all stars have.

Michael: Now the light that comes from different stars has different information embedded within it. The combination of colors that you see and also dark lines which you see in the spectrum of the star give us information about things like the temperature of the star, the chemical composition of the star, the size of it, and other important information that are used to figure out which stars are most suitable as locations around which life may exist.

Yvonne: OK. So let me explain this a little bit further. You can see that the blue star, the yellow star, and the red star all have the colored background of the rainbow. But look at the dark lines. There are different lines that appear for each one of these stars. Those dark lines are showing us that the chemicals inside the star absorb different amounts of light from that rainbow spectrum, so you will see the dark lines appear at different places for the different types of stars. A blue star is very, very hot. A red star is very cool. And our star, the Sun, is a yellow star, which is right in the middle.

Another representation of this same kind of information can be shown by another type of graph.

This is actually the kind of graph that I work with most often, and what we're trying to show here, and there's a lot of information here, so I'll try to make it very simple, but we're trying to show that the molecules and the chemicals inside of a star can give us information by showing in their XY axis you can see across the bottom here, they're wave length is light and across the y axis or up the side you can see how much light has been absorbed from that background rainbow color that you were looking at. And the bumps and wiggles that you see here tell us about the chemicals that are inside the star.

Here we're looking at carbon and hydrogen and we're looking at a comparison of dust -- we call it interstellar dust — that's within our galaxy, different galaxies, and also within meteorites, those objects that fall from space and fall to the Earth. And you can see that they're all very, very similar. So what we're studying is how similar is the organic material

That forms planets and that eventually falls to planets like the Earth. And if it's very similar in all the different locations where planets might form and if it has something to do with the origin of life on Earth, then we think we may have a better understanding in how life might have formed or might be forming on other planets.

Unknown female: Yvonne and Michael, we have a question from Sara in Mrs. Green's 6^th grade class. Are all the stars you see at night either red stars, blue stars, or yellow stars?

Yvonne: That's a great question. Thanks, Sara. We're glad to have this question. Sara wants to know — are all the stars same red, yellow or blue stars that we see at night. No, this is a very, very oversimplified presentation, and there's a great range and a great variety of stars out there. Most of the stars that you see when you look out in the night sky tend to be the big bright ones, but in reality most of the stars that are really there are actually even smaller than our star, the Sun, and they're not as bright and so that's why you don't see them. You will see more stars that are on the yellow down to red side of the color spectrum, but there are the bright, hot, very blue ones as well.

Unknown female: I have another question for you. This child didn't put her name, but would a prism separate the light from a flashlight into a spectrum?

Michael: Shall I repeat the question?

Yvonne: Yes.

Michael: The question is whether a prism could be used to separate the light from a flashlight into its various colors, and the answer is, yes, the light from a flashlight is just like the light that you get from a normal light bulb. It produces all the colors in the rainbow of the spectrum, and so if you pass that flashlight light through a prism, you should be able to see all the colors from red to violet in the visible spectrum.

Unknown female: A couple of more for you. Louise from Mr. Garcia's 5^th grade. Why are we looking for life on other planets?

Yvonne: OK. Louise wants to know why are we looking for life on other planets? I think that's just one of those questions that either you really care about or you don't. And in my experience most people do want to know whether or not we're alone in the universe. They want to know whether or not we're unique or whether or not they have a lot of friends out there, or maybe they're not friends. But, at any rate, we'd like to know whether or not we're alone, and so we're interested in studying how life started on Earth so that we can figure out whether or not it's studied some where else and maybe that's a question that matters to you and maybe it doesn't. Either way, that's OK But we're here today to tell you that it is a question that matters to us.

Unknown female: And one more from Tiffany in Ms. Brown's 6^th grade class. Did you have to know a lot of math to be an astronomer?

Michael: That's a good question, Tiffany. Yes, one of the most important skills that you need as an astronomer is the ability to do mathematical calculations, competence with the computer, and of course physics and some times chemistry are very important as well. In fact, most astronomers receive physics and mathematics training first before they proceed on in their astronomy careers.

Yvonne: In fact, that's probably a great segue into talking a little bit about our careers and how we got into doing what we're doing. So why don't we take a couple of minutes and just talk about that.

I'm an observer. That means I go to telescope and observatories around the world, take data, and then come back to my office and try to figure out what it means. Mike is a theoretician, so most of his work is done in front of a computer, and he does very complicated mathematics that he puts into our model and tries to explain the types of observations that someone like me would bring back. You need both.

You also need laboratory astrophysicists. Those are the people who mix up things in the laboratory and then look at them and try to figure out what it is that they're seeing. And when all three of those things come together, we think we understand a little bit more about the physical processes in the universe. So you can see why you would need to study a lot of math, a lot of chemistry, and especially a lot of physics. So you have to have that burning desire to understand science and then really apply yourself to make this happen.

Michael: One of the most important things about science to understand is that it's a practice where people like Yvonne collect data from, for instance, a star. People like the people in the laboratory do experiments in their lab, and people like me run experiments inside the computer. I teach the computer the physics that we think is going on in a particular star, for instance, and it's a collaborative process. Yvonne's data gives us some starting points, then the laboratory and computer models get refined, then Yvonne may go back and try to check one of the predictions of a computer model, and so there's this constant refinement and improvement of the detail with which we understand the physics and other processes that go on in stars.

Yvonne: And just in case you think maybe this is kind of boring, let me tell you what a typical day is like for me. A typical day is really a night spent at the observatory and my favorite place to go, not only because it's in Hawaii, but also because I can get the best data there, is on top of Mauna Kea on the big island of Hawaii. You're up at about 14,000 feet, so you're above a lot of the Earth's atmosphere, and we spend all night looking at the stars and sometimes studying things that nobody else has ever looked at before. And for me, that's just the greatest thrill. So I love my work, and I think one of the great benefits of having stayed in school and worked so hard all those years is that now I get to have something that's so much more than a job. It's even more than a career. It's just everything that I love to do.

Are there any more questions?

Unknown female: Yes, there are. From Jerome from Ms. Brown's 6^th grade class. Have you ever discovered a star or a planet?

Yvonne: Well, okay, I'll take a stab at that. I haven't discovered a star or a planet, but this graph that I was just showing you was probably the most exciting moment that I've ever had at the telescope because — I'll put it back up again and try to explain better what I mean.

Again, what we were looking at here and this is data that was collected over many, many years, what we looked at and suddenly realized was that the carbon and hydrogen atoms that we see inside a meteorite that in 1969 fell to the Earth and we can pick it up and study it, it has inside it the very same carbon and hydrogen configurations that we see in interstellar dust in the center of our galaxy some 30,000 light years away. And also this very thin line that you can see, it's kind of a yellowish color here, that represents the dust from a distant galaxy 2 million light years away. So they're all the same. And the moment that we realized they were all the same was just a very profound moment because it told us that there really may be a connection and, if there is a connection, then maybe there is life in the universe.

It's one very, very baby step towards getting to understand this, but for me it was really a profound moment because no one else had discovered that.

Unknown female: We have a question from Sara in Mrs. Green's class. She thanks you for answering her question and she wants to know, do you go to Hawaii, too, Michael.

Michael: Actually I have been several times. Like Yvonne said, I'm mostly a theorist; that is, I usually do calculations and try to understand the data that other people bring back, but I have several times been to Mauna Kea. I've viewed two different telescopes there. Last summer was the most recent time. And like Yvonne says, it's really a thrilling moment and one of the most fun things about the job. It's a strange environment; there aren't many people up there. The people who are there are very serious about the astronomy that they're doing, and there's just a strange good feeling that you get being in such a special place.

I've also been involved in several projects, which have used data from telescopes in space like the Hubble Space Telescope, another called the Infrared Space Observatory, which Yvonne has used as well. And in those cases, you don't go to the telescope. You make a proposal to use the telescope, then operators on the ground make the observations for you, and then you're just sent your data over the Internet and then you start analyzing it. So in a sense it's not quite as thrilling as going to the telescope, but it's also very exciting to be using these modern telescopes in space.

Yvonne: Right and while it's good to be up on top of a mountain because you're up above most of the Earth's atmosphere, it's even better if you can get all the way into space because then you don't have to worry about all the confusion of the Earth's atmosphere, you can just study the starlight and the lights on the interstellar dust or whatever it is you want to look at in an unencumbered way.

Unknown female: [inaudible] follows Timmy's question. Timmy from Ms. Whitmer's 5^th grade class. When you do observations do you get to look through a telescope or a camera?

Yvonne: When you make the observations today you're no longer looking at the end of an eyepiece of a very long telescope like in the old days. Now we sit here and we look at TV monitors, and some times you'll have a room full of 15 or 16 TV monitors, each one giving you another bit of information about how the telescope is working, how the instruments are working, and the data that you're getting from space.

Unknown female: Okay, we have a question from Nancy in Mr. Ruggiano's 6^th grade. If you find the yellow star, what do you do next?

Michael: Let me repeat the question. Nancy says if you find the yellow star, what do you do next? And that's an excellent lead in to the next section of what we're going to discuss here which is where are the prime places in which you might look for life around other stars? And let's see where we are on the graphics here.

So a term that we mentioned — why don't we go back to us for a second if that's all right?

A term that we mentioned right at the beginning of today and which I'll bring up again is the term "the habitable zone." The habitable zone is a term which tries to answer the question, where is it around the star that you might be able to find life? And the word "habitable" if you look it up in the dictionary means suitable for life. In other words, a location in which life might thrive. And astronomers and biologists as well have come up with a definition of the habitable zone, which is in very close concert with our idea of why life emerged here on Earth.

The simple definition is where would you put a planet around a star so that that planet would have liquid water on its surface? Liquid water seems to be one of the most important ingredients in the ability for life to have formed here on Earth and the fact that liquid water isn't present on other planets in our own solar system may be a clue as to why life hasn't emerged in those places.

Yvonne: Right. If I could just jump in here, I'd like to add that we think there are three things you really need in order to have life: liquid water, organic material, and energy. And all three of those things came together on the Earth and we have life. So now we're searching for liquid water. Also in our solar system we think we have some potential places, Mars is looking very good, for having had liquid water in the past, possibly even today, and Europa, the icy oceans of Europa, a satellite of Jupiter, may be the place that currently today has some sort of liquid water and liquid material.

Michael: Now one of the things that we can do once we've figured out what type of star we've found, that is whether it's a cool red star, a medium yellow star, or a hot blue star, is ask the question, how far from that star does a planet have to be in order for liquid water to exist on its surface. What I'm going to show here now is a calculation of what's called the habitable zone around a star just like our Sun.

Our Sun is a yellow star and the Earth lies about 93 million miles away from the Sun. Now astronomers don't like throwing the number 93 million miles around very much, so they've invented a new unit of measure when they talk about that distance. It's called one astronomical unit, so when I talk about one astronomical unit, I'm just talking about the distance between the Earth and the Sun.

Yvonne: So that's shown by AU on this graph.

Michael: That's right. Now the calculation that I'm showing here shows in green as a sort of Frisbee shaped disc around the star, the locations where a planet could support liquid water on its surface. The inner edge of the habitable zone in this particular case is at .9 AU, so just a little bit closer to the Sun than the Earth is and the outer limit is at about 1.5 AU, very close to where the planet Mars is located in our own solar system.

Yvonne: In fact, that's a good time to talk about what we call the Goldilocks phenomena, which is in our solar system Venus is just a little bit too close to the Sun and Mars is just a little bit too far away for them to have habitable zone conditions today or to be in a really good location for life today.

That doesn't mean that at times long ago in the early formation of the solar system they weren't in a more comfortable zone, but today they are just the Goldilocks scenario and we are the just right planet right in the middle where we needed to be.

Michael: Let me just follow up on that, Yvonne, by reminding you about the water issue. We think Venus, because it's closer to the Sun, lost all its water by evaporation. Essentially the water that may have existed on Venus all just boiled away into space, and so there's no possibility of liquid water on the surface of Venus. In fact, Venus is about 750 degrees on the surface. It's a very inhospitable and probably uninhabitable location in the solar system.

Mars is on the other end. Mars has water on it, but we're unsure yet how much of it may be liquid. Most people think that the water on Mars is frozen; it's sort of a perma frost on the surface, except that some of it evaporates away from its poles in the appropriate seasons and gets at least into the atmosphere as a gas. The conditions on Mars are not such right now that you could actually have a swimming pool of water on its surface. If you tried setting out a pool of water on the surface, it would very quickly evaporate away. So Venus is too close and has lost its water. Mars is too far and the water is in a frozen state.

Yvonne: But when we talk about Mars, and you might hear a lot of people talk about the potential of life on Mars even today, you can think about what would life have done if it had been there and we're talking about little microbes now. It would have gone underground. It would have gone deep down into the Martian surface in order to escape the very harsh conditions that are on the surface of Mars today. So we still want to go to Mars and take a sample of what's down underneath the ground and look and see if there could be any microbes there still today. And maybe there's just enough moisture for them to exist. We know that on Earth we find life in very extreme environments in places where you would never dream that something could live, deep down in the oceans floors at hydrothermal vents and in some very cold locations, so we want to look on Mars and see deep down under the surface. It's got the potential.

You must have lots of questions by now. Let's see if we can take one from . . .

Unknown female: We do have some questions for you. Nancy in Mr. Ruggiano's 6^th grade class asks could there be another liquid that would support life?

Michael: That's a good one.

Yvonne: That's a great one. You guys have been talking about this and thinking about this. I can tell. All right, Mike, take this.

Michael: Oh, thanks, Yvonne. It's certainly possibly. I'm going to dodge this question a little bit and say that I'm not a biologist, so I couldn't argue strongly that water is the only liquid that could support it. In fact, one of the interesting things that people are trying to find out now is that there's a moon of the planet Saturn called Titan, and there's a space craft called the Cassini Space Craft, actually the Hoygan Space Craft, which is part of the Cassini Mission, that's on its way to Saturn as we speak. And the Hoygan Space Craft is going to set down on the surface of Titan.

Now Titan probably doesn't have any liquid water, but it does have a chemical called methane, which is made of carbon and hydrogen, and on Titan we think the conditions are such that the methane could exist as a gas like water vapor in the Earth's atmosphere, as a liquid like our oceans, and also as an ice like snow. Now perhaps that combination will allow for other biological combinations to exist, but we simply don't know the answer to that question right now.

Yvonne: Right, and I can add to that that when we look up interstellar dust in space we see all sorts of ices mixed together. We have water right next to a methane molecule., That would be a carbon with four hydrogens. Or right next to some other types of carbons or carbons and oxygens that get together and form ices. They're kind of all mixed up together, and one question is: What happens when they fall to a planet and then melt? So it's possible, I think, that life could very well have originated in a condition that had some of these other things mixed in.

Unknown female: Another question here from Ricky in Ms. Aldane's 7^th grade class. Are there more yellow stars, or red stars, or blue stars?

Yvonne: OK, well this is similar to the answer I gave before. There are actually more red stars than anything else in the universe. The smaller stars that are less bright than our star, the Sun. But going all the way up to yellow, there's a continuum or a whole group of stars that you would find in that color range from red up to yellow and there are more of those than there are the bigger, brighter ones that go from yellow on up to blue.

Michael: That, again, is an excellent lead in to one more graph that I want to show.

The next figure here is a calculation of the habitable zone around one of these more common red stars, and as you can see, the red star which is a fainter object has its habitable zone a lot closer in than the habitable zone around the Sun. In this case, the habitable zone only extends out to about half the Sun-Earth distance or half an astronomical unit, and it extends way, way in — in fact, so close that I couldn't put the number on here — to about .05 astronomical units. So much, much closer to its star than for the Sun.

Now if you do the same calculation for a blue star, blue stars are the hottest and the most energetic of the stars that we study, and the result of that is that the habitable zone around a blue star moves farther out. So if you had a planet like Earth, one astronomical unit away from a blue star, it would be too close to that star to support water. The water would all boil away. You would have to have a planet further out, more than two astronomical units away from that star, up to about 4 1/2 astronomical units from the star in order for that planet to have the right conditions for liquid water.

Yvonne: So now you might think that since this is a much wider habitable zone that maybe what we really want to do is to be working on blue stars for habitable zones. But it turns out these stars don't live very long. They live life in the fast lane. They burn up all their energy very quickly, and so they die out probably faster than life could really get a good foothold and develop.

Michael: The earliest evidence for life on Earth that we have today indicates that life emerged several hundred million years after the Earth first formed. We know from studying the spectra and from looking at lots and lots of blue stars that they only live a million to maybe a couple of million years. So even if you had a planet in the habitable zone around one of these stars, that star would die out long before the planet had time to develop life on its surface.

Yvonne: Now a million years sounds like a long time to you, I'm sure, but think about the entire history of what we know of the universe, which is 15 billion years old, that's billion with a "b." So a million years compared to a billion years or even 15 billions years is actually a very, very short time. Our star, the Sun, has been around for about 5 billion years, and we have about 5 billion more to go. So you can see that if you have a star that only lived its life for about a million years. There just really wouldn't be nearly as much time for life to get started.

Michael: Now this brings up another interesting point that I want to raise, which is that the Sun doesn't produce the same amount of light throughout it's entire lifetime. We know that for the next few billion years, as Yvonne said, the Sun is pretty much going to keep doing exactly what it's doing. No need to try to move off of Earth anytime soon. Liquid water will be around for you and your children, your children's children, and for many generations to come. But we do know that about 3 billion years from now the Sun will start to change, and the total amount of energy coming out of it will go up, and as a result the habitable zone of the Sun will change. Eventually, in fact, the habitable zone will move away from the Earth and what that means is our very distant ancestors might have to move somewhere else.

At the same time that the Earth moves out of the habitable zone or the habitable zone moves away from the Earth, places like Jupiter and Saturn will move into it. Now Jupiter and Saturn themselves are not places which we think can support liquid water, they don't have surfaces and they're not made of exactly the right chemicals. But many of the satellites or the moons of Jupiter and Saturn do seem to have frozen water on them. When the habitable zone moves out into those regions, then those places might become habitable.

Yvonne: Right. And so maybe now is a good time to talk a little bit about some of the missions and some of the telescopes we use and things like that to try to explore these other worlds. Do you have a question for us?

Unknown female: Anna asks, and she's a 5^th grader, does it cost a lot of money to do spectroscopies?

Yvonne: Well, it depends on how you [phrase] it. Our telescope time on Mauna Kea, for instance, is very valuable and that's why people compete for it. You might have three or four proposals that compete for the same one night of observing time up there. So when we get there you want to make sure you've got everything ready to go and you have a backup plan, and if this doesn't work, you're ready to do something else so that you don't waste even one second of that very important time because it took a lot to build the telescope and to run it and to have the personnel there and all of that.

Then when you start talking about missions in space, you're talking about even more money because, of course, it takes a lot to build and develop and launch a mission. So I can't give you dollar figures because that isn't really something that I try to keep in my head. I know it's a lot of money, but I think when you compare it to what we get back, most people think it's worth what we're spending on it.

Michael: And maybe I can just follow up a little bit. You made the point that people are competing for single nights on the telescope. Some people have the impression that astronomers sit underneath the telescope day in and day out looking through a telescope and only spend a little bit of their time trying to understand the data. That couldn't be farther from the truth. In fact, astronomers are very happy if they get just a few nights' worth of data taking on the telescope. It can take months and months to understand what that data means, so the night on the telescope is important because you collect the data, but usually when you come home and start analyzing the data, that's when you put in the real labor. It's a time-consuming process, but one which is well worth it.

Unknown female: This is a follow up on that. Peter in Mr. Wheeler's 8^th grade class. What is the difference between space science and astrobiology?

Michael: It's an interesting question. Those of us who have worked here at NASA for awhile in what's called the "space science" branch feel like we've essentially been doing astrobiology for a long time, and we have been studying the chemical constituents of the universe in order to figure out whether the right raw materials are there in order to have life exist elsewhere. We've also been doing laboratory studies of those things, like Yvonne said, and pointing telescopes up at these sources in order to answer that very important question.

Now recently in the last few years the term astrobiology has been introduced in order to sort of summarize what it is that we do. So astrobiology is kind of what we already did. I should also say that there are plenty of people who are space scientists who are not answering the life questions. It's possible to study the atmosphere of a planet or the geology of a planet or the chemical constituents of a star, questions that don't necessarily go right at the question of is there life in the universe. But they're all very important components in our understanding. You need to know are there the right number of stars, where are the habitable zones of those stars, do they have the right raw materials to make planets around them, and, if so, are those planets capable of supporting life. So these are all questions that go into answering that question, the basic question of astrobiology. Is there life elsewhere in our solar system, in our galaxy, and in the universe?

Yvonne: I would just add that astrobiology is a subset of space science, but I would totally agree that basically it's all the same thing, just given a different name and maybe a slightly different packaging every few years. Astrochemistry, astrobiology, and astronomy in general, even astrophysics, it's all so closely related today. We're trying to understand the physics and the chemistry, and if there's biology, we're trying to understand the biology of the universe, too.

Unknown female: Here's a question. They didn't identify who they are, but it says, when do you think we will find a habitable planet?

Michael: This is another excellent lead in. One of the things that's most exciting to me about astronomy, astrobiology, space science and the like is that we really do make a lot of progress. Now when I first started studying astronomy as an undergraduate student, there was a lot of speculation about what the chemical components might be out in the universe. People were starting to discover the raw materials that might support life, but no one had really successfully attached the question of are there really planets available on which that life could form.

Now about sixty years ago, the very first experiments that confirmed the existence of planets around stars started to come to fruition. They released their data and we now know that there are something like 80 stars around which there are planets. Now that doesn't mean that only those 80 have planets around them. Those are the only ones for which we have direct evidence, but using that direct evidence we can infer that many, many stars have planets around them.

Fifteen years ago we knew that some of the chemical components for life were available. Now we're starting to find planets around other stars, but those planets that we found are probably not the right kind of planet. They tend to be planets like Jupiter that are very big balls of gas, which aren't like the Earth. They don't have solid surfaces that probably don't have liquid water on them and so they probably can't support life. However, there are a whole series of missions whose goal is to try to find those habitable planets. NASA set the goal a year or two ago of finding and even taking an image of a habitable planet in something like the next 20 to 25 years. If that goal is met, then everyone in your class will be around when we discover the first one.

Yvonne: I think that's an absolutely great time to start talking about some of these missions because we don't want to leave you today without telling you about some of the great things that you have in store for you. And should we start with the order that we have them in?

Okay, we're just going to show you very quickly the ground base telescopes. These are on top of Mauna Kea, like we've been talking about. These are called the Keck twin telescopes. They're both 10 meters in diameter as far as the collecting area for the starlight and these are probably among the most powerful telescopes in the world today. So that's in Hawaii.

Michael: And maybe I could follow up on that by saying that in the upcoming lessons that you'll be discussing in Astro Venture, one of the things that will be discussed is how do you actually find a planet around one of these stars and the Keg telescopes are being used as we speak to try to discover more planets around more stars to help to answer this very question.

Yvonne: OK, so now let's look at the next telescope a little bit and go a little bit higher, but still not into space, we get to our next great observatory and this is in the back of a 747 jet. This is called Sophia, the Stratosphere Conservatory for Infrared Astronomy. That's where the name Sophia comes from. And this is almost ready to fly; it's not yet ready. In a few more years it will be going and astronomers will be on board and you can see the telescope at the back end of the plane, so you're up above almost all of the Earth's atmosphere, but not quite all of it. And you can fly around for seven or eight hours and collect data.

There was an airplane somewhat like this that we used for many years until just a few years ago. It wasn't quite as big and the telescope wasn't as big, but that's where I got a lot of my thesis data for my Ph.D. and it's really exciting to fly up on the airplane like this. The only one of its kind in the whole world, and if you're interested in astronomy, it's very possible that you may end up working with astronomers or flying on it yourself because there will be a lot of education programs that will work with Sophia.

Michael: This is an interesting one. Right here at NASA Ames a group of scientists just won a competition to have a telescope built and this telescope is called the Kepler Telescope, named after a famous astronomer who first figured out the motions of planets here in our own solar system, and the Kepler mission will be looking for planets that are about the size of the Earth by using a very interesting technique. What they're going to do is stare at a large number of stars and look carefully for the very slight dimming of starlight that occurs if a planet passes in front of it. Essentially the planet will form a very, very small eclipse and the amount of light reaching us from the star will dip down just for a couple of hours as the planet moves in front of it. From the amount that the starlight drops, you can tell things like how far the planet is from it's star and also how big the planet is and start to get a handle on how many Earth-size planets there are and see whether they're in the right place, whether they're in the habitable zone.

Yvonne: And, again, that's something that you'll learn about in the next AstroVentures that you have here. You'll have a couple of other people talking to you about the details of how one actually goes about doing that.

Michael: This is a graphic showing a telescope called SIRTEF. It's the Space Infrared Telescope Facility. It's going to be launched, I believe, at the end of 2003, and it's going to be in what they call an Earth-trailing orbit. You may be able to see that in the graphic here. The telescope is going to be launched from Earth and will fall gradually behind the Earth as it progresses. It's an infrared telescope, which means it's very good at looking for not necessarily individual plants but the raw materials out of which planets are believed to form. We know that very early in the life of a star, a star forms a disc of material around it, and that disc is the raw material out of which planets form, and SIRTEF will be excellent detecting these discs and helping us to answer even more completely the question: Do all stars form planets around them and, if so, how many of those planets are in the habitable zone?

Maybe we'll just show you one more here. This is a graphic of another telescope in space called the Space Interferometry Mission. One of the biggest problems in trying to find something relatively small like an Earth size planet around a star is that the light from the star tends to completely block out your view of that planet. One of the ways that you can compete against that, one of the ways you can help improve your vision, is to build a telescope that can see extremely small details, and the way that you do that is by building the biggest telescope possible.

The SIM mission, which will go up in a couple of years, is just a technology demonstration mission which will have two telescopes separated on either side of the space craft and those two telescopes will act as a giant eye, able to see very, very small details. This is a sort of a test mission in preparation for another one which is at least a decade away called the Terrestrial Planet Finder, which will be a huge telescope with sides of the telescope separated by — I don't remember what the number is, but it's enormous distances. It will be located out near the orbit of Jupiter, and it should be able to at least attempt the first images of planets around other stars.

Yvonne: And there are other missions that we're not even talking about today. This is a very exciting time to be an astronomer or for you to be thinking about it or to be studying math and science because, whether or not you go into astronomy, you could pick any science field and it will somehow be impacted by the kinds of discoveries that we're talking about here today. I think it's just a wonderful time to be alive in spite of all the terrible things that are going on in the world. I think astronomy is one of those things that gives us hope for the future and the missions that we're describing to you here I think should lift everybody up.

Unknown female: We have some more questions if this is a good time. David in Mr. Whitmer's class says: Do other habitable planets have years about as long as ours?

Yvonne: We don't know. First of all, we don't know if we have habitable planets, but it will really depend a lot on where they're located. Probably if you're talking about a star like our Sun and then the habitable zone would be similar to where ours is located, yeah, they probably have a year kind of similar to ours.

Michael: We simply don't know the answer. But we do know, however, that if a planet is around a star like the Sun and it's one astronomical unit away, it will take 365 days to go around it. So if it's in that spot, it will have the same year as the Earth. We just don't know; we haven't found one yet, but we're looking.

Unknown female: Okay, and then Bonnie in Mr. Wheeler's 8^th grade class. When did you know that you wanted to be an astrobiologist?

Yvonne: Well, I knew when I was about ten years old. I grew up in Key West, Florida, and one of the advantages to that was that every time the Apollo missions were launched, if it was in the daytime, I could run outside and on a clear day you could see it go overhead. So I remember very clearly standing in my backyard, looking up at the sky and telling my Dad that some day I was going to work for NASA and be part of the space program. And I'm sure everyone thought, yeah, yeah, cute little kid. Well, we'll see what she does. And so it's really kind of fun that I actually ended up doing that. I didn't know how I was going to get there, but I knew that I wanted to be part of this really great, exciting thing. It was the most extraordinary thing I could imagine doing.

Michael: One of my earliest memories was watching Neil Armstrong step off of the Lunar Lander and take the first steps on the Moon, and I also remember from a very young age being fascinated by the night time sky and then later by the space shuttle program, and that's what got me interested in physics and astronomy and led to the career that I have now.

Yvonne: Also, I'd like to add that it's not like it was easy along the way, and there were so many times that I thought, I can't do this; this is too hard, and I'm not going to make it and the math is just overwhelming. The thing that sets the people who succeed apart from the ones who don't is that you have to be a very determined person. You have to want this very, very much, and so then you don't have to be that brilliant student who easily gets everything and makes straight A's. You just have to be the tenacious one, the one who won't let go, the one who does every problem in the book, not just the ones that the teacher assigns. If you're that kind of person, nothing is going to stop you.

Unknown female: We have even more questions. Let me ask you. Ann from Ms. Webster's 7^th grade science. How big is the Moon compared to the Sun?

Michael: One of the easy ways . . . this is something that I talk about quite often with students. One of the easy ways to remember the relationship between the Earth and the Sun is that the Earth is 1/100 the diameter of the Sun. Now the Earth is a much, much smaller fraction of the amount of material, but it would take you a hundred Earths to march across the diameter of the Sun.

Now the Moon is one quarter that diameter, which means that the Moon is 1/400^th the diameter of the Sun. And an interesting little about that is that you may be familiar with a phenomenon called a solar eclipse. That's when the Moon moves in front of the Sun and blocks all of its light. Now in order for that to happen, the smaller Moon has to be a lot closer to us than the Sun is. In fact, the Moon is almost exactly 400 times closer and so, even though its 400 times smaller, can block out the 400 times bigger Sun. So that's a convoluted answer to the question, but 1/100 is the ratio between the Sun and the Earth. One fourth is the ratio between the Earth and the Moon, so 1/400 is the ratio between the Sun and the Moon.

Yvonne: But when you look up at the sky and you see the Moon and some times you see the Moon in the day time, I want you to notice that some time, you look at the size of the Moon and you look at the size of the Sun, they actually appear as though they're same, and it's just that the Moon is that much closer to us and the Sun is that much further away. But they look like they are the same; in fact, they're not. The Moon is much, much smaller.

Unknown female: We have a question from Marie in Ms. Aldane's class. Would you like to travel in space?

Michael: Absolutely. I don't think there's one among us who wouldn't say that. Absolutely. Sign us up.

Yvonne: Definitely.

Unknown female: We have another question here. Do you need to know biology?

Yvonne: It would be helpful. Right now I wish that I had spent more time in my biology classes. I took two years of it in high school, and I really didn't revisit it at all in college. Now it's turning out to be a very interesting aspect of what we're doing. Chemistry right now for me is more important than biology, but I can see the trend going towards the more we understand about life starting on Earth, the more I'm going to need to know about biology.

Michael: One of the nice things about our line of work as well is that we're constantly learning new things. You're sort of an eternal student if you're an astronomer. We're always going to talks by our colleagues and learning about details of their own work, and as I went through graduate school, it was obvious that I would have to learn some more chemistry even though I was getting well versed in physics and mathematics and astronomy. But I had to teach a computer some chemistry, so I had to learn some more of that. Now that biology and chemistry and mathematics and space science are all coming together, we're going to more and more talks about biology and becoming more educated about it, and that's a lot of fun.

Unknown female: A question from Mark in Ms. Richley's 6^th grade. Do you like science fiction and who's your favorite author?

Yvonne: Well, I'm not really that much of a science fiction buff, although I was a great Star Trek fan of the original series. And Star Wars, of course, I loved. And I did read the Dunes Trilogy or series. I loved that. How about you, Mike?

Michael: Yeah, Yvonne could have answered that question for me. I went through a brief stage when I was about thirteen-years-old where I was very interested in science fiction. And I read many of the classic Asimov and Bradbury stories. But then I got interested in novels, non-science fiction novels, and I enjoy reading those. So interests change and some astronomers love it. I know some who — in fact a colleague of mine just published his first book, and I read that one.

Yvonne: And I'm working on a murder mystery novel. So I love books, but science fiction, I guess it's just that the real stuff is so much fun that I don't spend as much time reading science fiction. But I can certainly understand why that would be appealing. I think we might need to be wrapping this up. I can see our time is almost over. Do we have time for a couple more?

Michael: Sure. Why not?

Unknown female: Here's one that says, hi, my name is [Nassar] and I'm in 9^th grade in the [inaudible] School of Science and Technology. Do you believe that the Sun is heating up and could cause global warming?

Michael: That's a good question. We do know that the Sun goes through cycles and that the amount of energy coming out of the Sun does change over the course of what's called the 11-year solar cycle. However, there seems to be very strong evidence that environmental factors here on Earth are more important in changing the climate on Earth than those changes in the Sun. Those changes in the Sun repeat on a fairly regular basis, but we do know that the Earth has been warming up on a time scale that's very different from the time scale during which the Sun changes its power output. So at least from the information that I know, it's more likely that environmental factors here on Earth are responsible for the warming that we're experiencing.

Yvonne: Yeah, I'd like to add that I think this is just one of the most serious questions we have facing us, and I saw a wonderful graphic today that showed all of the planets of the solar system with the Earth with a pair of hands holding it. And I just think that's something that we all need to keep in our minds every day because what we're doing to this very special planet is serious, and we need to take care of it. Global warming is a real problem and we're doing it.

Unknown female: I do have one last question from Megan in Ms. Westbury's Lakeside Middle School in South Carolina. What exactly is the Aurora or Northern Lights? Where did they come from?

Michael: I'd be happy to take it. The Sun is constantly letting off a stream of particles. The Sun is made mostly out of hydrogen atoms and those hydrogen atoms have what are called protons in the center of them. The Sun is always spitting out some amount of those protons. They travel across the distance between the Sun and the Earth at one astronomical unit in about 4 1/2 days or so and when those particles crash into the gases in our atmosphere, they cause those gases to glow and give off that very beautiful stream of light that we call the Aurora borealis. The reason that you only see them in the far north or the far south is that the Earth's magnetic field prevents those protons from crashing into the atmosphere in places like the Equator. So the protons come in, they skim along the magnetic field, and the only place they can get in is near the North or South Poles, so that's where we tend to get the Northern Aurora borealis and Southern Aurora australis.

Yvonne: OK, well it's been fun being here today. Thanks so much.

Michael: Thank you very much. Bye, bye.