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# Donald Burnett

Donald Burnett

### Professor of Nuclear Geochemistry, Emeritus

By David Zierler, Director of the Caltech Heritage Project

August 24 and September 6, 2021

DAVID ZIERLER: OK, this is David Zierler, Director of the Caltech Heritage Project. It is August 24, 2021. I'm delighted to be here with Professor Donald S. Burnett. Don, it's great to see you. Thank you for joining me today.

DONALD BURNETT: You're quite welcome.

ZIERLER: To start, would you please tell me your title and institutional affiliation?

BURNETT: Well, this actually goes way back. You've probably read about Bob Sharp, who was a very famous division chairman. He scratched his head to find a title for me. My background's a little different from most. He came up with the idea that I was going to be an Assistant Professor of Nuclear Geochemistry. And I think that's officially on the list, but over the years, it evolved into just Professor of Geochemistry. The nuclear part became pretty irrelevant.

ZIERLER: Were you the first, and are there any other professors of nuclear geochemistry?

BURNETT: No. Probably the first and last ever. Bob was a very creative person. He wanted to try to come up with something that fit me. And that's what he came up with.

ZIERLER: What is nuclear geochemistry?

BURNETT: [laugh] It's a Bob Sharp creation. My degree is in what is called nuclear chemistry. I never took a geology course in my life. My PhD was with Glenn Seaborg at UC Berkeley. But then, I wanted to change my emphasis, and that's when I came to Caltech. But my official degree says I'm a nuclear chemist from UC Berkeley, and there's a long line of people from that profession from there.

ZIERLER: Another term that's been associated with your career is cosmochemistry. I wonder if you can explain that term.

BURNETT: Oh, my goodness. I have no connection to this. It goes back to Harold Urey, very famous chemist and Nobel Prize winner for the discovery of deuterium. He's appropriately regarded as the founder of modern planetary science. But he was a chemist, and he emphasized the chemical aspects, because they were his specialty. He founded a journal. And it goes back to about 1956. He called it Geo- and Cosmochemistry. Cosmochemistry was a word that Urey defined as focusing on the study of materials that were not terrestrial in origin. In fact, it was the study of meteorites primarily then, but it's broadened into planetary science. So anything beyond the earth. Today, it's a very accepted thing but it's still primarily focused on our solar system, despite the "cosmo". In 1956, it was way out beyond, so it was called cosmochemistry.

ZIERLER: Maybe an easier answer is, at dinner parties, when people ask what kind of scientist you are, what do you tell a more lay audience?

BURNETT: I say there's a sign on the door that says I'm a professor of geochemistry. That even requires explanation in many cases.

ZIERLER: [laughs] Just for a snapshot in time, what are you currently working on, or what's interesting to you in the field?

BURNETT: I still am working primarily on the results from the Genesis mission. This was the mission that we started in the early 90s. It was officially approved in 1997. It returned in 2004, and the materials from that give us a sample of the sun in the form of the solar wind. We are still working on those samples. And we have a lot to do. There's a lot more we can do. It's been rather difficult to do this. There was a famous reentry crash when the spacecraft returned in 2004, and that broke up a lot of our materials we had used to collect the solar wind. But the solar wind's atoms–you can't destroy atoms with a crash. On the other hand, you can cover them up, contaminate them, and hide them. And we've been slowly unraveling this over all the years. And we have made steady progress, and we're still going strong, actually.

ZIERLER: I wonder if you can explain, all these years later, why there's still data to be taken from the mission. How much data is there? What does that tell us more broadly?

BURNETT: Let's put it this way. There are 92 elements, and geochemistry, as you probably know, does not deal with just the elements and their abundances, but also the proportions of the different isotopes. In fact, isotopic geochemistry is a huge field. It dominates the field of geochemistry to this day. Solar wind isotopes were always very difficult measurements, but it looked feasible. The crash made it that much harder, and it's taken us this much time to learn how to handle the samples and to get the data with the required precision. Ours was a mission which involved measuring things, but the measurements had to be done to a certain accuracy. And that's been the challenge over the years, to not just detect the solar wind. "Oh, yeah, there's a solar wind atom. You can see it there." It's how much of it was there, and with a very high degree of accuracy. That's been what's challenging us.

ZIERLER: What were some of the major research questions at the heart of this mission, and to what extent have they been answered so far?

BURNETT: We had an original list of 19 "measurement objectives" because they were involved with measuring a specific thing. Then, we had a connection to a scientific question for each. The highest priority was to measure the oxygen isotopic composition of the solar wind. The second-highest priority was to measure the nitrogen isotopic composition of the solar wind. The third-highest priority was to measure the isotopic compositions of the noble gases. So you see, isotopes dominated. Now, we have done these three, plus many others. Other isotopes are important. We have done Mg. Fe can be done. Carbon still escapes us because the way that we planned to do the carbon involved measuring large areas of silicon samples. And that was severely hurt by the crash. It's still feasible. There are still ways to do this. It's on the list, and we or somebody else at some point will pick us up.

ZIERLER: Are there current missions or missions that are being planned that will continue this line of research?

BURNETT: No, this was a one-of thing. Now, there are ways it could be done better, but let's not get off into that.

ZIERLER: A broad question. What role does theory play in your work?

BURNETT: Well, it's very important. We are geochemists. We are interested in the relative amounts of the abundances of elements and their isotopes in the sun via the solar wind. But we knew from the very beginning we could not do this mission right without input from solar physicists, from both the theoretical and observational sides. A major partner with us in Genesis was Marcia Neugebauer. I'm sure you know about Gerry Neugebauer, a very famous astrophysicist. Marcia Neugebauer was equally famous. She was one of the discoverers of the solar wind. She was at JPL. Very distinguished person.

Her input made us do it right. She said, "What you have is fine, but it's not good enough. What you have to do is this. There are three kinds of solar wind, and we have to know their compositions independently." And so, we took a deep breath and said, "Yes, ma'am" Then we did it. We actually brought back samples of these three different kinds of solar wind. And doing those was figured into our number three objective, which we did, through the noble gases. It's been done for another element or two as well.

ZIERLER: I wonder if you could explain a little bit the significance of the discovery of solar wind.

BURNETT: Oh, my gosh. [laugh] It was suspected because the tails on comets are oriented to point away from the sun. The tail of a comet is a collection of gas and dust. The only way people could figure out why the comet tails pointed away from the sun was that there was plasma coming out of the sun which was shaping the gas and dust being emitted from the comet into this long tail. The idea of a solar wind was sitting out there until Marcia, and other people, in the early 1960s, said, "Let's put a spacecraft out. We'll show that solar wind exists, and we'll measure its properties." And they did. This was about 1964. Marcia was a good theorist, but she was primarily an observationalist.

But theory is also very important to us and has been all along because what you get from the solar wind coming out from the sun actually has a certain bias, what we call "mass fractionation". This was recognized by Ed Stone, a Caltech professor of physics, director of JPL, very distinguished person. He first discovered, not from solar wind, but from energetic solar flare particles coming out of the sun, that there is a compositional bias in the higher-energy particles. It was later shown to be in the solar wind as well, so that the ratio of two elements coming out of the sun wasn't exactly what it was in the sun. The magnitude depends which element pair you look at it. It could be large, factors of two or three, if you pick the right element pairs.

So we knew that fractionation was present, and we had to have ways to characterize it. One of the main ways was the different samples of the solar wind. We had a theory from Peter Bochsler, which to finally answer your question about theory, did a good job predicting the difference in the ratio of two isotopes of neon in what we call the fast solar wind and the slow solar wind. There is a definite theoretical prediction what that should be. And what we measured was actually pretty close to that. That gave us a method for correcting for isotope fractionation. It's a long, involved, complicated thing. But continued input from theorists to this day is important to relate what we have learned about the composition of the sun, the origin of the solar wind, and to help us correct our data to get what we want out of it. And there is feedback to increased understanding of solar wind and solar physis. So there's a very good symbiotic relationship between the theory, solar physics, and us.

ZIERLER: With the proliferation of observations, and missions, and all of the data to analyze, how have computers aided your research and analysis of all of this data?

BURNETT: [laugh] I sit at home with my life's work on my little Mac laptop. I still have lots and lots of Genesis data to process. What I do is fuss around with Excel for hours in a day. But it's trivial stuff compared to what other people do. Computers are obviously very important. This is not my field. You're talking to the wrong person here. But this is obviously very important. Not just for theory, too. Almost all modern instruments are computer-based. All the very elaborate mass spectrometers that people have in the geology division are computer-controlled.

ZIERLER: To get a sense of the size of your laboratory, as it were, is your research focused exclusively on our solar system? Or to what extent can you extrapolate what you learn close by for the interstellar medium, or even other galaxies or solar systems?

BURNETT: Comparisons are interesting, but what I've always worked on is strictly confined to what's in our solar system. There's plenty there to do. And it's a very interesting place.

ZIERLER: And that extends to what, the sun and all eight or nine planets?

BURNETT: All of these different little moons in the outer solar system, nearest I can tell, are all different! In the early 70s, when they began to explore the solar system, I was expecting them to be a bunch of ice cubes. Wrong. Every one of them is different, and fascinating, and has its own evolution. We live in a first-class solar system.

ZIERLER: What's the big takeaway from that, the fact that there are all of these distinctions, even within our solar system? What does that tell us more broadly?

BURNETT: It's important, and a fascinating challenge, to find out why they're different. Of course, when you find out why they're different, that tells you how they got that way. These differences, which are both physical and chemical, are the clues to understanding how the solar system works and evolved. Chemical data over the years has played a major role in planetary science, and always will.

ZIERLER: What role do you play even in an emeritus status at Caltech? Do you sit on committees? Do you advise students?

BURNETT: No, I haven't advised a student in a long time. I officially retired about 2006, something like that. I only have contact with students through the class I teach, and I serve, now, on only one committee, which is the Institute of Radiation Safety Committee, of which I'm a chair. And basically, I always brag a little, I'm the best qualified person to chair that committee. I know the background, and I'm from a division different from the one where most of the radioactivity is, which is good in a regulatory committee. So, I keep that job. We have an outstanding radiation safety office. And it doesn't take a lot of my time. But I still keep the chair of that one committee.

ZIERLER: What is the mission of that committee? What is it designed to do?

BURNETT: Well, the handling of radioactive materials is set by regulation, mainly by the State of California, on how it will be done. There are limits. It has to be monitored and controlled. The amounts used at Caltech are small and not particularly dangerous. But because they are potentially dangerous, there are state and federal regulations, and every university has to have a radiation safety officer who controls and keeps track of the amounts of radioactivity to make sure it's used safely and to control its disposal.

ZIERLER: Does this include JPL? Or that's separate?

BURNETT: No, JPL has their own separate Radiation Safety Office.

ZIERLER: Building on that, I'm curious, generally, how valuable has it been for you to have JPL so close by?

BURNETT: Well, I ran a mission with JPL. In the period from, let's say, 1995 to 2005, something like that, I was up there almost every day. And beyond that, JPL and I pretty much parted ways. On the other hand, JPL played a major role. Obviously, mission management and operations were done through JPL. Somewhat uniquely, our hardware was built at JPL, although there were major instruments from LANL. We were different in a lot of respects. Genesis was one of the Discovery's small mission series. It was all handled pretty much within JPL, with the spacecraft being built through Lockheed Martin.

ZIERLER: More recently, how has your science been affected one way or another by the pandemic and remote work? In other words, not traveling or seeing your colleagues.

BURNETT: Conferences are very, very important. We've learned to do the Zoom equivalent of conferences. And we're going to keep those because they have some great advantages. On the other hand, the ability to sit down and talk to individual people for an hour is irreplaceable. You can play the presentations and things like that, that's fine. But what you can't get is the one-on-one conversation with people who know things that you want to know and vice versa. That's very difficult to reproduce. We try with Zoom, but it's just very difficult. Having laboratories shut down slowed us down quite a bit, and still does, to some extent.

ZIERLER: Well, let's take it all the way back to the beginning. Let's start, first, with your parents. Tell me about them.

BURNETT: I come from Dayton, Ohio, from a small town in the Midwest. My dad was a civil servant for the Air Force. Dayton is the site of the Wright-Patterson Air Force Base. He took a job there just before World War II. He was marginally old enough not to be drafted. Also, he had a critical defense role. He worked in what we call today a cryogenic lab. He had a high school education, basically, but he learned. His facility filled the oxygen cylinders for the aircraft in World War II, very important. They had to be able to cryogenically separate oxygen and nitrogen. He worked with liquid nitrogen, actually, which for somebody in 1941, was a very rare thing.

And then, once the war over, he went on to have various jobs with the Air Force until he finally retired in the late1960s, My mother had an 8th-grade education. In the 1920s, that was, in many cases, enough. But by the 1950s, she returned to work. As a young woman, she had worked in the National Cash Register factory in Dayton, which was very famous locally for being very enlightened towards its employees. It was a strange mix. It was enlightened out self-interest because they were deeply afraid of being unionized. But their response was to treat their employees quite well. And that was accepted. She was happy there. That's where she met my father. And then, as required, she had to quit after she was married. A woman could not be married and work in 1935 in the Dayton factories. That was just the policy there. They hid the fact they were married a year or so. And then, she finally did quit.

But later on, as I got into high school, it was pretty boring for her to sit around the house. So she went back, she took a job selling little girls' dresses at the major department store in Dayton, a job she loved. She loved that job. And she was so happy doing that. And she did that for many, many years until they transferred my father in the late 1950s, and they had to move to Newark. She was never happy there, but when my father finally retired, they moved back to Dayton. They were wonderful people. I was the only child, and I highly recommend being an only child [laugh] as it has huge advantages. My generation was spread out through time, and when I was growing up. I was the only child in a very large family. Boy, was that a good thing. So I had a very happy childhood.

ZIERLER: It sounds like your father had some pretty strong innate technical and even mathematical skills. Is your sense that, with better economic opportunities, he would've pursued higher education?

BURNETT: Quite possibly. He always had an interest in chemistry, and that did influence me.

ZIERLER: What year were you born?

BURNETT: 1937. Long time ago.

ZIERLER: What are some of your memories of World War II as a young boy?

BURNETT: Oh, a lot. I was 7 years old in 1944, and that was in the final stages of the war. In the Dayton Daily News, I followed the maps as everything was going on both in Europe and the Pacific quite thoroughly.

ZIERLER: Was your family home more in a rural environment, a suburban environment?

BURNETT: It was transitional. My father grew up on a farm. My mother's father was listed in the 1910 census as a ditch digger, basically. But it was a small blue-collar town ten miles north of Dayton, which was a small city then. My high school had 75 people in my graduating class. But again, most of the people there really weren't farmers. They were living in what now has become a major suburb of Dayton over the years. But then, it was in a transition to that stage.

ZIERLER: Were you always interested in science, even as a young boy?

BURNETT: Yes. I'm not one of these people who had trouble figuring out what to do. I was exposed to my first science class in the 6th grade, and I said, "This is fun. This is something I want to do." And then, as I went on through high school, I said, "Well, I like chemistry best. I'm going to be a chemist." All these major decisions of what to do with your life, I never had difficulty with them. It was all, in retrospect, compared to other people I've seen, so easy.

ZIERLER: Did you have chemistry sets at home? Did you like to tinker with things?

BURNETT: No, I never got one. I don't really know why. I toyed with the idea one time, but we never got it. I think my mother was a bit frightened of them, so we never did.

BURNETT: Oh, boy. Like many people, I'm sitting before you as a result of a lot of random collisions, accidental things. I knew I wanted to go into science. I knew nobody in my family had ever gone to college. I subscribed to the equivalent of Science News. It may have still been the Science News at that time. And everything interesting was going on at the University of Chicago. But it didn't seem possible that I could go there. But one day, I was at some event, and I don't even remember why, in one of the big high schools in Dayton. I wandered into their library. I looked on the shelf, and there was a catalogue for the University of Chicago. It said it was possible to get a scholarship to the University of Chicago.

So I went home, and I applied. Then, in 1955, before all the standardized tests, the University of Chicago did its own standardized tests. I got this letter that said, "Show up in Cincinnati," which was 60 miles south of me, on such-and-such Saturday morning, and take our entrance exam." Well, that day started out with a blizzard. And my dad said, "We're going." So we got in the car. He drove, we slipped and slid. I was two hours late getting to the exam. But they said, "No problem. There are only four people. Sit over here. You can start now and take it."

Well, I took this exam, and it was all on writers, and poets, and musicians, humanities things that I'd never heard of. On the other hand, I had taken a lot of multiple-choice tests. Ohio was big on multiple choice tests. And so, I guessed at a lot of answers, but I came back and said, "Well, that was a waste of time," put in my application to Ohio State, and didn't think twice about it. Lo and behold, I ended up with a scholarship to the University of Chicago.

ZIERLER: Did you have an appreciation for Chicago's role in World War II? Was that something that you were aware of?

BURNETT: No, not really. I learned about that afterwards. I was looking at what was happening scientifically in the 1950s. But particularly chemistry was very prominent at the University of Chicago. And all the interesting things seemed to be happening there.

ZIERLER: What was it like moving to a big city like Chicago?

BURNETT: Well, the university was fairly isolated on the south side, and the situation in the late 1950s in the surrounding neighborhoods was fairly tense. So you didn't wander around very much. We did, but we were told you were taking your life in your hands to do it. Everything was pretty much centered in the university itself. But you could take the elevated train down to the Loop, which we did occasionally for concerts, plays, and things like that. But not much else. Gradually, I learned a little bit about the city over the course of the years, through random trips out and things like that. But the university was pretty much an island in those days.

ZIERLER: And was the plan to study chemistry from the beginning? Or did you have a more general education approach?

BURNETT: Nope. I signed up as a chemistry major from the beginning.

ZIERLER: Who were some of the professors that stand out in your memory from undergraduate days?

BURNETT: Oh, we're back to Harold Urey again. He taught freshman chemistry. And he also taught physical chemistry. He retired soon after that--this was probably 1955-1958--and moved to La Jolla, where he spent the rest of his life still doing very distinguished work. I got to know many of the people in the chemistry department fairly well.

ZIERLER: What was Urey working on when you were an undergraduate?

BURNETT: He was working on many important things. He wrote a very important paper with Hans Suess on the abundances of elements in the solar system in 1956, which it turns out, you can relate back to nuclear processes in stars. He was working on that. I didn't know that then. As a teacher, he didn't do very well. Many of the other students were not very happy with him. When he was teaching something he really wasn't interested in, stuff like electrochemistry, he would fumble around in the book and have trouble with it. But when he got on something he knew about, that was different. When he started carbon-14 or deuterium in the ocean, it was wonderful stuff. So, I had great respect and admiration for him. But there were many, many other professors there who were very influential on me. The most important one, because I had this inherent interest in radioactivity, nuclear processes, was Nathan Sugarman, who was a professor of nuclear chemistry. He was a veteran of the Manhattan Project, which I didn't know until afterwards. And he taught the nuclear chemistry course. I talked with him many times about what to do, where to go, things like that. He was very influential. And at that time, new on the faculty a couple years before, there was Ed Anders, who became the dominant person in studying meteoritics, cosmochemistry, from 1960 until almost 1990. I never took a course from him. On the other hand, I did talk to him a couple times about what to do. I was very aware of his work and how interesting it was to me.

ZIERLER: What laboratory opportunities did you have as an undergraduate?

BURNETT: [laugh] I worked my junior year in a laboratory of Norman Nachtrieb, who was a professor of physical chemistry. I took an analytical chemistry course from him. And that was very interesting. He walked in and said, "All right, you know how to blow glass, don't you?" "No, sir." "Well, here, it's easy." He took this big piece of glass several inches around. "Here's how you do it. See that? Go do it." Well, I struggled for days and days. I was a total klutz at blowing glass. Finally, he said, "OK, this colleague of mine needs help calculating things. You can do that." His name was Schultz, something like that. I did calculations and helped him with some of experiments. But I was a total klutz there doing anything experimentally.

Then, after my senior year, I got a job at Argonne National Labs. I lived near the university and took the bus out to Argonne every morning, which was about a two-hour drive. Argonne is 30 miles southwest of the south side of Chicago, something like that. I was in the chemical engineering division. The first thing they said to do was, "Take these samples and seal them off in glass." I said, "OK. There, I did it again." And I stumbled and struggled, and I finally got a couple things sealed. Fortunately, they had a good glass budget. Then they said, "Well, you know about radioactivity. We want to measure very small concentrations of zirconium. Why don't you put them in a nuclear reactor and do it?" So I did that, and it worked out very well. They were very happy with that. But finally, I escaped blowing glass. But I did have research opportunities in Chicago, and I got a lot out of them.

ZIERLER: As an undergraduate, were you interested in outer space? Or was your chemistry curriculum really earth-based?

BURNETT: It evolved. As I was a senior there, I began to hear of some of the interesting things going on in the study of meteorites, and in particular, what Ed Anders was doing. So I went to talk to him. I said, "I'm very interested in this kind of stuff." He said, "Well, this is not the stuff for anybody that's not already a scientist," in so many words. He said, "This is a very speculative thing. You want to learn how to make an honest living first. Go get your degree in nuclear chemistry. If you're still interested in that, then you can do meteoritics afterwards." And that's exactly what I did. Now, both Sugarman and Anders wanted me to go to Columbia to work with a fellow named Jack Miller, who was a very distinguished nuclear chemist. But he was the only one at Columbia. I also read about all the things going on at Berkeley. And so, I took their advice, but I didn't take their advice. I went to learn to make an honest living before I went into cosmochemistry as a nuclear chemist. But, I went to UC Berkeley, not to Columbia. And yes, I did learn how to make an honest living as a nuclear chemist.

ZIERLER: What impact did the Sputnik mission have on you and the opportunities that might've come afterward?

BURNETT: We got up in the middle of the night and watched Sputnik come over in the 1950s. It was big and bright enough you could even see it in the Chicago sky if you knew where and when to look. It was moving really fast. But, nothing really directly. Of course, the effects it had on the nation, particularly on the stimulation of technology, which was directed towards spaceflight, but spilled over into many other fields. And of course, Sputnik was associated with the Cold War. And the Cold War led to strong support for anything in the nuclear field at the time. The labs I went to in Berkeley were very well-supported.

ZIERLER: What was it specifically about Berkeley that was so attractive to you for graduate school?

BURNETT: There were a lot of different people working there in different parts of nuclear chemistry. In the chemistry division--this is probably true to this day and was particularly true then--you were expected, when you walked in the door, to not only know what field you were going in, but who you were going to work for. You were mature enough as a graduate student that you knew what you were going to do. "Get on with it, and let's get you out of here." I couldn't make up my mind who to work for. I took a whole semester at Berkeley. And they were having faculty meetings about me. "What's this guy doing? He's screwing around here."

So I was feeling the pressure. I finally made a decision, and I talked to various people about what was then the University of California Radiation Lab, which was just up the hill over the top of the campus. Many of the people up there had actually worked with Seaborg at many times, and there were a bunch of research labs. I ended up working with a fellow named Stan Thompson. I found what he was doing very interesting. But that meant I was officially a student of Seaborg's. I signed up and was going to be working on nuclear fission, which sounded pretty interesting. I finally decided that in January, and everybody was happy after that. I was the last person to sign on to somebody. Seaborg, at that time, was the chancellor. I went down to his office, and he said, "Well, you signed up with me. If you want somebody who's going to work side by side with you day and night, you're in the wrong place. On the other hand, if you want to work on interesting science up at the lab, and I will check up on you every now and then, if you're willing to work by yourself and with the other people"–I said, "I don't have any problem with that."

ZIERLER: Was your sense that Seaborg maintained an active research agenda while he was chancellor?

BURNETT: In a very high-level way. Let me digress and talk about him a little bit. This was 1960. I went to Berkeley in the fall of 1959. The 1960 election, of course, brought the end of Republican control of the government. And Seaborg was then appointed chair of the Atomic Energy Commission by Kennedy. And so, he was not only not around the lab, he was back in Washington most of the time of my graduate career. But he would come through once a year, something like that, and we would talk. It came time to write my thesis. I wrote it. I called him up on the phone and said, "Well, I have this thesis ready." He said, "Send it quick. I've got a flight to Norway, and I have nothing to do. I'll read it on the flight."

The thesis exams were done remotely. A committee read your thesis and made comments on it. There was no exam, meeting, oral presentation, or anything like that. He was the first person to finish reading and sign it because of that flight to Norway. Then, the most interesting thing was, after Nixon came to power in 1968, and of course, as a Democrat, Seaborg was out. Seaborg came back to Berkeley and picked up doing research. This was a man who had been a chancellor, the chair of the Atomic Energy Commission, been away from day-to-day science for years, who came back and went back to it. I have great admiration for him for that. But it made my claim to fame as being his last graduate student no longer true. For several years, I had that as a claim to fame.

ZIERLER: Given his physical absence, did you have any de facto advisors closer to campus?

BURNETT: I did not work in a vacuum. I was in Stan Thompson's research group. Stan was a wonderful person. He was a radiochemist. He was the discoverer of Californium. He had several people work with him. And he basically let us do what we wanted to. We picked problems, he would think about them, give some comments here and there, and tell us where to go to get to do these things. The other person I worked with very strongly was a theorist who was in the physics division, an expatriate Pole, Wladyslaw Swiatecki, who was an absolutely brilliant theorist. His papers are the most readable things you can find on the topic. He could take complicated things and make them very simple.

I would go to him and say, "Here's this great idea I have." He'd say, "Ah, you're making arbitrary assumptions. Go back and do something better." [laugh] He influenced very much. There were other people there who worked with Swiatecki directly at the same time that went on to really make major contributions on the nature of fission and led to some of the basic ideas we have about superheavy elements today. But I split off by about that time. I did learn that I was an incompetent theorist.

ZIERLER: What were some of the bigger questions in the field at the time, and how was your thesis research responsive to some of those questions?

BURNETT: Well, one of the biggest questions in fission was the origin of the so-called mass asymmetry. In nuclear fission, the nucleus splits into two parts, but it doesn't do it equally. It doesn't split into two equal-sized fragments. It splits into a light fragment and a heavy fragment. There was no theoretical explanation for this mass distribution. It was generally believed, and is still believed today, that something happens in the course of the dynamics of this very highly vibrating nucleus as it fissions. It chooses a pathway among hundreds of different pathways it can go, which is primarily asymmetric. It's not in the beginning part, it's not in the end part, it's in the intervening part, which is very, very difficult to treat theoretically.

That was one of the major issues. One clue was that there was a transition between fission of what we call the actinide elements, uranium and thorium, which is primarily asymmetric. But as you went to "lighter" elements like lead and bismuth, it became primarily symmetric. Another difference was, to induce fission in an element like lead or bismuth, you had to supply a lot of energy to make the nucleus fission. If you did the same thing to uranium and thorium, the fission became symmetric there also. The transition between asymmetric and symmetric fission was both as a function of energy for uranium and thorium and at any energy where you could measure it for lead and bismuth.

I studied the charged-particle-induced fission of bismuth and gold, and some experiments also with uranium and thorium as function of energy, looking at the mass distributions as a function of energy going through these transitions. And I was fortunate to be able to have access to very elaborate kinds of electronics that were state of the art at the time. I did more computer programming as a graduate than I've ever done since. I didn't solve the problem of fission mass asymmetry, but I did provide important systematics on the asymmetry to symmetry transition.

ZIERLER: I wonder if you can explain what computer programming looked like in the early 1960s. Was it Fortran?

ZIERLER: Were there any national security implications to this research?

BURNETT: No. I was in a place where there was almost no classified work going on. Most of that was done at Livermore. There were a couple of nuclear tests that were still going on in the early 1960s. And nuclear tests had been one way to make elements much heavier than uranium and thorium. And that's what some of the people at Berkeley worked on. We had some materials, and Stan was bound that I was going to learn some real wet radiochemistry. And so, we had one of these tests. Me and the other graduate students were begrudgingly involved in having to learn all this wet chemistry. We were all doing things with detectors and electronics. Anyway, we went through it, but the bombs never worked. At least, the tests never gave us anything that we could measure.

BURNETT: Oh, yeah. The whole development of what's very common today: a semiconductor p-n junction as a radiation detector. The Berkeley Lab was pioneering making these things. So I had a factory that kept turning out the latest detectors for me to play with the whole time there. Yes, that was very, very important.

ZIERLER: Besides Seaborg, who else was on your thesis committee?

BURNETT: I had three people on the committee. Two of the three people were Nobel Prize winners. I had Emilio Segré, who was a nuclear physicist, and I had taken a nuclear physics course from him. He was happy enough to make an offer to switch to high energy nuclear physics. I was flattered, but wisely as it turned out, I declined. The third person was John Rasmussen a nuclear chemist. Two of the three were Nobel Prize winners. That's a bit of a claim to fame.

ZIERLER: Anything memorable from the oral defense?

BURNETT: There wasn't any. You submitted your thesis in writing, they sent you back comments, and that was it.

ZIERLER: Was this because of where Seaborg was? Or that was standard practice?

BURNETT: No, that was standard procedure. They did not have oral exams for thesis exams. We had an oral qualifying exam, like most divisions of Caltech do today. But not for a thesis defense. It was all done on paper.

ZIERLER: Wrapping up in 1963, I'm curious if in Berkeley the counterculture movement started at all. Was anybody worried about Vietnam, that kind of thing? Or is that too early?

BURNETT: That was brewing. When I left Berkeley in 1963, it was just starting. But the whole issue of peace protests, weapons research, security clearances were major issues on campus. I went to some of the talks on these things.

ZIERLER: Were you politically engaged at all?

BURNETT: I was politically active, but not politically engaged. I was conscious. I followed political things starting pretty strongly, starting in the 1960 election. At Berkeley, I listened to KPFK, which covered radical politics, all the time.

ZIERLER: What opportunities were available to you after Berkeley? Where had you considered going?

BURNETT: That, again, was fairly easy. Working with Stan Thompson, he had collaborated with Willy Fowler on some of the ideas associated with the origin of the elements, nucleosynthesis processes. Fowler had explored the idea that the decay of a supernova, which has about a 60-day half-life, was due to Californium-254, which has a 60-day half-life. Turns out, the decay is due to a half-life, but it's not Californium-254, it's Nickel-56. Stan, of course, had been one of the discoverers of Californium. Stan had interacted with Willy Fowler and Fred Hoyle at that point. And he gave me a copy of their very famous paper, B-squared-F-H, Burbidge, Burbidge, Fowler, and Hoyle. I read this cover to cover and said, "That's the most interesting thing I've ever seen."

ZIERLER: Why? What was so compelling to you?

BURNETT: I'd been interested in elemental abundances and sort of semi-followed the work on meteorites, the discovery of iodine-129 by John Reynolds (at Berkeley) and things like that. Then, I read that you could put these elemental abundances in meteorites together with nuclear processes that formed the elements in stars. So I said, "Gee, is there anything I can do with this?" I wrote Willy Fowler, I said, "Here I am, I'm a chemist, and I'm very interested. Is there any possibility you would consider me as a post-doc?" And he said, "Oh, I have a great problem here. It involves chemistry, meteorites, and things like that." "Yes, yes." So then, I came to Caltech.

ZIERLER: What was it about meteorites that was so central for this research?

BURNETT: Because "chondritic" meteorites have an elemental composition which is very much like what's in the sun. In fact, today, there's one particular kind of chondrite whose composition is used as solar composition for almost all the elements. Not hydrogen or helium, but almost all the nonvolatile elements. Amazing thing. A rock falls in the sky, and it has the composition of the sun. Even today, the meteorite data are more accurate than those from measuring the sun directly. There are reasons why you should believe this, and there are reasons why it might go wrong occasionally. So, meteorite abundances played a major role. I had this interest in meteorites all along. When this came up and combined the two things I was really interested in, meteorites and nuclear processes, that's when I decided, "Well, if there's any chance, that's what I would like to do."

ZIERLER: What could you know, before the more modern space missions, about meteorites?

BURNETT: This was the subject of the Urey and Suess paper in 1956. You had the spectroscopic abundances from the sun. You had all the spectroscopic lines, which could be analyzed in terms of relative abundances. You don't get the most accurate data, but you got a good, broad picture of the element abundances. And there were patterns. It wasn't random. There were peaks and valleys in it. It was Suess and Urey who recognized these peaks, and it was Burbidge, Burbidge, Fowler, and Hoyle who explained what they were due to. They were due to processes in the stars. All these abundances were inherited from the stars that preceded the formation of the sun. And that, to me, was the most exciting thing I'd ever heard of. Because, like I said, it combined the two things I was most interested in, meteorites and nuclear processes. I could use what I knew to go into a new area, which I wanted to go into.

ZIERLER: What division was Fowler in at that time?

BURNETT: Physics. He was a physicist all the way.

ZIERLER: What was he like as a person? What was it like to work with him?

BURNETT: Oh, it was fun. He was a great person. He would go and tell someone, "Oh, this is wonderful. Greatest thing I've ever heard. Most wonderful thing. Keep on doing that. Keep on doing that." Something like that. And he was always very positive like that. I wrote a paper with him and Fred Hoyle, which actually destroyed one of his theories about how the isotopes of lithium-beryllium-boron formed. And he had no problem with that.

ZIERLER: Did Fowler have a large group? Were you his only post-doc at the time?

BURNETT: No. This is Kellogg Radiation Laboratory. There must be a history of it. If you haven't seen it already, you should look at it. I was a small part of it then. It was going strong around 1960. It was run by Charlie and Tommy Lauritsen. Charlie was getting on in years, but he was still there. Tommy was really the person who ran Kellogg until probably the middle to late 60s, something like that. I knew them. They were there. I didn't work closely with either of them.

There was still a lot of work. They had a tandem van de Graaff accelerator in the basement of Sloan, next door to Kellogg. And there were still a lot of nuclear physics experiments going on. I would interact with the nuclear physicists. I got to know them. Later on, I actually did some experiments with the van de Graaf.

ZIERLER: What were the results of your research on meteorites?

BURNETT: Well, it came from the nucleosynthesis side, and it involved the elements of lithium-beryllium-boron. Willy had this idea that the isotopes of lithium, beryllium and boron were formed by nuclear reactions involving particles from the sun interacting with the solar nebula. But once you got into it, the details just didn't work out. Then, we said, "Well, we can test this. If this is right, then you would see isotopic variations in potassium that would be due to this." And that's when I moved into geology. And I hooked up with Gerry Wasserberg, and we measured these, and they weren't there. Willy was happy. He had this sign that said, "Isn't it nice that beautiful theories are destroyed by horrible facts?" He had no problem having something disproved.

ZIERLER: What was the direction of your research that led you to Gerry Wasserberg?

BURNETT: The study of potassium isotopes.

ZIERLER: And what was Gerry working on at that time?

BURNETT: The University of Chicago had infected Caltech. Initiated by Bob Sharp, Wasserberg, Sam Epstein, Clair Patterson and Harrison Brown had moved from Chicago to start geochemistry at Caltech. Wasserberg had developed the technique of potassium-argon dating for his thesis with Harold Urey as his thesis advisor in Chicago. He moved to Caltech, set up a potassium-argon lab, but he also got interested in trying to date things with rubidium and strontium. He was sharing mass spectrometers with Clair Patterson, so-called solid source mass spectrometers. You analyze a solid by putting a little bit of it on a hot filament, heating it up, and through thermal ionization, measure the ions coming off. We adapted that to potassium. He said, "You're a chemist. You can learn how to separate potassium from meteorites." "Yeah, I can do that." And I did. And it worked out fine.

ZIERLER: Now, you formally became a post-doc of Gerry's?

BURNETT: No. I was always a post-doc with Fowler. And then, when I moved to geology, it was as an assistant professor.

ZIERLER: Oh, I see. What were the circumstances of you being offered a faculty position?

BURNETT: You'd have to talk to Bob Sharp about that. But they decided I was interesting enough that they were willing to keep me. My post-doc was coming to an end, and I was applying to places for jobs. I think Wasserberg started this, and then Fowler supported him. They decided that I would fit in with the division in terms of my background and my interests.

ZIERLER: Tell me about your work with Hans Lippolt using the mass spectrometer that Clair Patterson developed.

BURNETT: That's the potassium work. It was proving a definite prediction from Fowler's theory. And it just wasn't there. We did find some other things. And then, things evolved.

ZIERLER: What year did you join the faculty?

BURNETT: [laugh] '65 or '66. I think '65.

ZIERLER: And was it still the Division of Geological and Planetary Sciences then?

BURNETT: No, I don't think so. I think the name change happened in '67, '68. I think it was just the Division of Geology then. Bob Sharp said, "We're bigger than that now." He wanted to change the name of the division to the Division of Planetary Sciences. He said, "We're just one of the planets now. We have all this work we've started here, which is going to be great and going to be very important in planetary science. We should call ourselves the Division of Planetary Science." Now, the geologists balked at that. [laugh] So the name is a compromise. It was the Division of Geological and Planetary Sciences. The geologists did not want to lose their connection with geology. So we had this hybrid name. Everybody's been happy with that since.

ZIERLER: What was your research at the time you joined the faculty? What were you working on?

BURNETT: I was working with Gerry. There were reports that the iron meteorites were five billion years old, but everything else in the solar system at that time was believed to be 4.6 billion years old. Gerry knew that there were some iron meteorites that had silicate inclusions, i.e., rocky material in them which had Rb and Sr. With the silicate inclusions, we could check whether these ages were five billion years or 4.6 like everything else. We pursued Rb-Sr dating of meteorites very profitably for about four or five years. And almost everything came out 4.6. That worked out very well.

ZIERLER: In the field of geochronology, was this important for determining broader questions like the age of planets or even the universe itself?

BURNETT: Let's back up a little bit. It was very important in determining the ages of planetary materials. 4.6 billion years old was first obtained, probably, by Wasserberg from his potassium-argon days for his thesis. Then, it came out with Clair Patterson's work of lead isotopes on earth that the earth probably had that age also. That became the number to try to work with and to refine, probably by the end of the 1950s in order to to see age differences in meteorites. We now know they're only millions to tens of millions of years from this number, 4.6 billion.

ZIERLER: What was the value of mass spectrometry in this?

BURNETT: That was the only way to do it. You had to see the effects of changes in the isotopic composition produced by radioactive decay, e.g.. the changes in the relative amounts of strontium-87 from the decay of rubidium-87. You had to measure the isotopic composition of strontium, then you measured the elemental ratio of rubidium to strontium. That allowed you to calculate an age. The mass spectrometers were absolutely essential. There's no other way to do it.

BURNETT: He had already done it. He did that in the late 50s I think. I came on the scene in the middle 60s. He was off doing other things. But I knew him very well. We became good friends over the years.

ZIERLER: And was he involved in your research at all?

BURNETT: We never did anything jointly. But at one point, I ended up with the office, which I still have today, called 100 North Mudd. It is the first office on your left as you came in the door of North Mudd from Wilson. Every day, if I was there, Patterson would drop in and chat. Same with Sam Epstein, too. These were great people. They would always stop in and chat with me a little bit about something. And so, I got to know Patterson quite well then. But this was into the 80s and 90s.

ZIERLER: As the space race was heating up, the prospect of manned missions to the moon and even further beyond, in what ways was that relevant for your research?

BURNETT: That was very, very important. Being at the right age and in the right place at the right time doesn't hurt. Wasserberg was heavily involved in what was going to be done with the lunar samples once they were brought back from the Apollo missions. We moved on from working on meteorites to getting prepared to actually measure ages and other things on lunar rocks. In addition to measuring the ages, we put together other things you could measure there, and it was easy to get money then. And then, most importantly, Wasserberg had this idea for a digital mass spectrometer.

All the mass spectrometers then were analog machines. Data came out on a strip chart, and you had to measure the thing with a magnifying glass to get the most accuracy out of the peak on the strip chart, which digitally, you could do at least an order of magnitude better. And Gerry realized that. He brought on Dimitri Papanastassiou, who is very important to the history of Caltech and science. Dimitri actually built the first digital mass spectrometer for his thesis. And the world has not looked back since then.

ZIERLER: What was so revolutionary about a digital mass spectrometer?

BURNETT: You could get a lot more data at the same time. In other words, you could step the magnet fairly fast, and then get a lot of counts in a certain period of time, then step onto the next isotope mass peak, and keep doing it time, after time, after time. On a strip chart, we might have, in a good day, 25 ratios, something like that. You would have 250 or more with digital. It was brute force. You could get more data faster, get more information out of a sample. And the fast-stepping magnet was very important, too. So it wasn't just the digital part of that. This revolutionized everything.

ZIERLER: Did you work with Gene Shoemaker at all during these years?

BURNETT: No, I didn't work with him directly, but I knew Gene quite well, of course. He was deeply involved in the Apollo program. He was chair of the division. I knew Gene very well.

ZIERLER: Tell me about the significance of Paul Pellas coming on board.

BURNETT: That's a funny connection. He was French. He was someone Gerry knew well, and I knew well, and a very, very distinguished mineralogist from France. He had a very good eye. He could pick out this mineral called whitlockite, which is calcium phosphate. Nobody else could. And he would have a little bag of it. He'd say, "Look what I got here. Wouldn't you like some of this?" And Gerry said, "We're going to do that." Gerry had taught mineralogy and also had a very good eye. He was very good with the microscope. He learned how to do this, too.

So he sat down with Pellas and learned how to do it. And he set about separating all the whitlockite grains from a powdered meteorite sample. The issue was, what we call now short-lived radioactive nuclei, which are nuclei which are radioactive but had lifetimes too short to survive in nature today. One of the most famous ones, that people thought was alive when meteorites formed, was plutonium-244. 244Pu had a very characteristic signature. It decayed by a process known as spontaneous fission. At that time, Gerry's noble gas lab, under the direction of Jack Huneke, had evolved to measure xenon isotopes very well. And so, Gerry picked out the whitlockite, and Jack measured the xenon. My role was fairly minor. I did some fission track work there, just to show the fission connection. 244Pu was the source of the fission tracks.

So we could produce the fission tracks and the fission xenon all together. It was a very important result. It showed that the plutonium-244 was really present in the early solar system. Pellas never participated in it directly. He made many visits here. I knew him very well.

ZIERLER: Tell me about being a witness to the Apollo program and even the moon landing itself. What were those events like for you?

BURNETT: Oh, it was amazing. I was at the right place at the right time. Like I said, Gerry was closely involved in this, and Dimitri and I would take care of the lab back here. He was spending most of the time in Houston. And we were doing experiments. We knew what we wanted to measure. We were doing experiments to get ready for these. In the spring of '69, Gerry was pretty much in Houston full-time. So we could follow things on the inside. And in July '69, on television, there they were, walking on the surface of the moon. "It'll never work. It'll never happen. Something will go wrong. This will never happen." Then, "Oh, my God, the rocks are coming back. It's really going to happen. We're really going to be able to study these things." And that dominated my life, from 1969 through probably 1976, something like that.

ZIERLER: What was the value of actually having a human land on the moon scientifically for your field, and not just having a probe go and grab samples?

BURNETT: You had the geological context. That was best done in Apollo 17 with Jack Schmidt, who had a Caltech connection. You have the ability to move around; the ability just to be able to grab a rock and photograph it. Eventually, the astronauts were trained to know what kinds of things to look for. Lee Silver from Caltech played a major role in the training. Particularly in the later missions, Apollo 15 and 17, this turned out to be very important. It's very difficult to have a computer tell you everything you want to know instead of a person who's trained at it and knows what to look for. Because the computer camera would be looking over here, when the real interesting rock is over there, sometimes far away. And in terms of collecting samples, a human still probably can't be beat.

ZIERLER: What were some of the big questions you hoped would be answered once you got your hands on the lunar rocks?

BURNETT: The ages. We knew that these were volcanic rocks that had formed in lunar mare. The rocks were inferred to be young because the mare had a much lower density of impact craters. By knowing the relative crater rates on the earth and assuming these were the same for the moon, Gene predicted that the mare rocks were going to be 100 million years old or something like that. He was off by a huge factor. They were over three billion years old. That was the major issue. The lab was focused on that. But we were doing a lot of other things, too.

BURNETT: I think there's pretty much consensus on how it formed, today. That didn't occur until 10-15 years later. And it came more from the physics side rather than the properties of the rocks, although some of the chemical properties of the moon were important to the ideas of the giant impact. But all that came about in the 1980s, more from the theoretical and astrophysical side.

ZIERLER: Did you engage with Dave Stevenson at all on these questions?

BURNETT: I know Dave quite well, I've talked to him many times, but I'm not sure we ever talked directly about giant impact at that time, no.

ZIERLER: Was the expectation after the Apollo moon landing that there would be more?

BURNETT: Depends on whom you're talking to. [laugh] We knew that Apollo was going to end. You could return samples much more cost-effectively by doing it robotically. The way the Chinese are doing it now is the way it should've been done after that. But it never happened. Something always got in the way. None of us never convinced NASA that it was worth doing. What the Chinese are doing now is what should've been done all along, from the 1980s on.

ZIERLER: Was the technology there?

BURNETT: I think so. The Soviets basically did it this way in the early 1970s.

ZIERLER: When you did finally get those samples from the moon, what answers were resolved, and what new questions were raised as a result?

BURNETT: Well, the most interesting thing was that the ages of the mare were much older than people thought. The evolutionary time, the rate at which things were happening on the moon was very fast early, and then it sort of shut down after that. The thermal history of the moon as a planet was totally unanticipated. When you compare the cratering rates--again, this is something Wasserberg had done later on with Dimitri in the late 1980s from the lead isotopes--the actual cratering rate was very high back of four billion years compared to today. Wasserburg referred to this as the "terminal cataclysm", which had no basis in terms of planetary dynamics then, but does now in terms of planet migration, motion of Neptune causing a flood of bodies from the outer solar system, bombarding the inner solar system at about 3.9 years, a long time after the solar system formed. The idea of this terminal cataclysm has got a lot of support these days.

ZIERLER: Was the idea that you could extrapolate what you learned from the moon to other planetary satellites? Or did you know even then how different things would be, even in our own solar system?

BURNETT: In the early 70s, the first inclination of what was present on Mars was coming out. I always had the idea that everything is different. And certainly, Mars looked like a very different planet than the moon. And the more and more you saw about other planets, they were all very different as well. The large body of knowledge about the Moon is an important point of reference.

ZIERLER: On that point, what were the next space missions that were most interesting to you?

BURNETT: I think in the 1970s, we always hoped that there would be a Mars sample return. That never worked out. But then, in the 1980s, I began to get the idea of a solar wind sample return. So I started working on this and promoting this idea about 1984. And eventually, it actually happened.

ZIERLER: And that's a great place to end for today.

[End of recording]

ZIERLER: This is David Zierler, Director of the Caltech Heritage Project. It is September 6, 2021. I am delighted to be back with Professor Donald S. Burnett. Don, it's good to see you again.

BURNETT: OK.

ZIERLER: To start, I'd like to return to the early 1980s. As an entree to the Genesis mission, let's engage in a little Solar Winds 101. First, what are solar winds? How do you target them? How do you capture them? And then what do they tell you once you've successfully done that?

BURNETT: That covers a lot of ground. The solar wind represents the fact that the outer parts of the sun are gravitationally unbound. In other words, the outer parts of the sun escape. They have enough energy, and the temperature is high enough so that they escape out into space. This was recognized theoretically in the 1950s, and proved by the work of Marcia Neugebauer at JPL, by direct spacecraft observation in the 1960s. The way you target it is very easy. The solar wind flows out through the solar system, and it goes past the earth. All we have to do is get away from the earth's magnetic field, get a little bit further out from the earth, turn towards the sun, and there it is. It's there all the time. You just have to go out and pick it up.

We collect it because it's going at a relatively high velocity, and when it hits a material, it'll implant itself and stick. All this was known from studies of ion implantation in the laboratory for many, many years. We could predict quite confidently that the solar wind would stick. There was a little bit of backscattering, but this was a small correction we knew how to make. And so, all we have to do is stick a material out in front of the solar wind, and it will collect itself for us.

Now, this material has to be very pure because the number of atoms per square centimeter, what we call a fluence, is fairly low. We want the solar wind signature to be much, much higher than any natural contamination of background, so we required a very high purity of materials. But semiconductor-grade silicon is a very pure material and serves as an adequate collector for almost all the elements, obviously not silicon itself.

ZIERLER: Why wind? What does that connote? Does it have a flow to it?

BURNETT: Yes, yes. I've never been asked that question before. But I think that's basically the answer. The material is gravitationally unbound. It flows out from the sun, so it is, in effect, a wind. Now, it's a plasma. It's ionized. But it is a wind.

BURNETT: Well, there's been a long series of spacecraft measurements of the composition of solar wind. And I'd followed this quite closely. I had been in contact with Marcia all through this time. In the late 1970s, I said, "Well, when will the rest of the Periodic Table be available?" She said, "Probably never in your lifetime. It's just too hard to measure." And so, we decided that we were going to try to measure this. We started thinking about it, like I said, in the early 1980s.

ZIERLER: Was JPL always going to be central for this project?

BURNETT: Because of her, yes.

ZIERLER: What could you do at JPL that would not be possible elsewhere?

BURNETT: Well, it probably was possible elsewhere. But it was the devil we knew. And she knew her way around. That part of the story is very detailed. I'll stop there.

ZIERLER: What were some of the big questions at the origin of the Genesis mission?

BURNETT: Genesis involves measuring both isotopes and elements. Isotopes are atoms of the same element, same atomic number, but they have different weights. For example, with oxygen, you have oxygen-16, which has an atomic nucleus with eight protons and eight neutrons, then oxygen-17, which is eight protons and nine neutrons, and oxygen-18, which is eight protons and ten neutrons. The eight protons make an atom oxygen, but the weights vary according to the number of neutrons in the nucleus. We didn't expect to find any new elements or isotopes. That was not going to happen. We knew that. But the proportions of the isotopes and additionally the proportions of elements, which is the chemical composition of the solar wind, is the direct link to the chemical composition of the sun. These were the big questions we were after.

ZIERLER: Is it assumed that what the sun does is what every star does with regard to solar winds?

BURNETT: Qualitatively, yes. In detail, I'm sure not.

ZIERLER: What does it tell us at all about the formation of planets?

BURNETT: The composition of the Sun is assumed to be the composition of the solar nebula from which all planetary materials formed. You can think of ways in which this might not be true, but it appears to be a good working hypothesis. In turn the chemical (and isotopic) compositions of different planetary materials is a major clue to how they formed if you know what the starting composition was.

ZIERLER: Can you explain a little bit about the process from going to a raw idea, to a proposal, to NASA saying, "Go"? How does that process work?

BURNETT: I think there's no general explanation. I'll just tell you what happened in our case. We wrote our first abstract…

ZIERLER: Who are the key people working with you?

BURNETT: Marcia and I at this point. Carol Zolensky, a grad student in planetary science who I think went on to work at JPL. She helped us do some calculations. One of the first things people said was, "You put a material out, it's going to be smashed to bits by micrometeorite impacts." We went through the literature, Carol did that for us, and it wasn't going to be important. And in fact, it really wasn't. That was 1984. That was the first abstract talking about a solar wind sample return mission. That was to the Lunar Planetary Science Conference, which is the big event in our field every March. Went on for 50 years until the pandemic shut it down for two years.

Then, it was a matter of lobbying. I would lobby at every opportunity for the possibility of a solar wind sample return mission. It was basically going nowhere until in the early 90s. In 1991, '92, NASA started what are called Discovery Missions. These are small, PI-led missions that were simple enough to be affordable. This fit exactly what we were trying to do. At that time, I raised enough money to hire as a post-doc at Caltech. Roger Wiens, who moved on to Los Alamos, stayed with Genesis, and has now become a major player in all the Mars Rover missions. He came to Caltech in the early 90s, and we started working on some of the details of how we were going to do various things.

Then, around 1992, there was this conference at San Juan Capistrano, where all the different people who had ideas for Discovery missions proposed something, and we made our pitch there. Then, there were ten missions selected for second study, and we weren't one of them. And the report back said, "This would be a good mission, but the ACE mission in 1998 is going to do all this." Which was totally wrong. And I sent to the chairman of the review panel, "If you're going to reject us, do it for the right reason. This is totally wrong." And by God, we were put in as number 11 to get a certain amount of funding to do some concept studies. It always helps to protest a little bit every now and then.

So, we were one of the "concept missions" that got selected for a little bit of advanced NASA funding. JPL, in addition, financed a whole bunch more, and other places did, too. And then, there was a main proposal written in, let's say, 1993, '94, '95, something like that. The first three Discovery missions were selected by NASA. The fourth Discovery missions was competed for, and we lost out to the Stardust mission by Don Brownlee for Discovery 4. It was done in two stages. There were three proposals selected, Brownlee's, ours, and a Venus mission.

And then, we had a separate round of presentations and things. And following that, they selected Brownlee. But we basically came in a close second. And so, we were all ready to go when the Discovery 5 announcement came out, and we were selected there. So we were Discovery 5. Our funding started in late 1997.

ZIERLER: How did you see Genesis overall as part of the Discovery missions? Where did it fit in?

BURNETT: It fit perfectly. It was very small; it was simple. Today, it'd be a very low-cost mission, but even in those days, it was a fairly low-cost mission. We were competitive price-wise. I don't think we were the cheapest one ever, but we were competitive. We were not cheap because we had to bring a sample back. That was a big deal.

ZIERLER: A general question about the overall budgetary environment at the time regarding basic science. With the cancellation of the SSC and the end of the Cold War, did these sorts of large-scale issues affect the kind of science that you wanted to do?

BURNETT: Not at our level, no. But they affected the direction of NASA at the time, yes.

ZIERLER: What was the process by which Lockheed was selected to build it?

BURNETT: The sample collection hardware was built at JPL. JPL did manage and do the trajectory and spacecraft operations. But the actual spacecraft was built at Lockheed Martin. They were selected primarily because I knew Ben Clark very well, and I knew he was interested in sample returns. And Lockheed Martin had acquired a company that had some experience in parachute reentry. It was just a natural fit all the way for them to do the spacecraft. They also did Stardust, so there was some synergy there.

ZIERLER: What was so important about capturing a sample to bring back? Why couldn't this stuff be analyzed remotely?

BURNETT: It can, in principle. But the instruments don't have the sensitivity and precision. The isotopic composition variations we're talking about were parts in a thousand, and there's no way you can touch that with a spacecraft instrument. We proposed, and we were correct, that we could do this much more precisely than you could with any kind of spacecraft instrument.

ZIERLER: When did you get the word that this mission was ready to launch?

BURNETT: Well, we started funding in December 1997. We were scheduled to launch in March of 2001. But somebody at NASA decided, "We don't want them launching ahead of the Mars mission," the one that was going to launch in 2001. "We don't want to have to worry about them getting in trouble." So they gave us extra money to postpone the launch. We had a lot of launch windows, but it wasn't perfect. We ended up having to move from March to August, but NASA supplied the money to keep us going through that time.

ZIERLER: What was the decision-making process like for determining Genesis's trajectory and flight plan?

BURNETT: The logical place to study the sun is something called the L1 Lagrangian Point. This is the point in the solar system where the gravitational forces from the earth and sun balance each other. The earth weighs a lot less, so this point's going to be very close to the earth. It's a potential energy minimum, and a very good place to put a spacecraft. It just sort of naturally falls in there. This had been done for solar-observing spacecraft for many, many years. It was basically a parking lot out there. Coming back, though, was a different matter. We got major help from someone at APL, which is one of Lockheed's competitors. But he was generous enough to share his calculations with the people at Lockheed Martin. He'd figured out how to return a spacecraft from L1, and we used what he did. It involved some complicated things I don't even remember now. Looping back around the earth and coming in at the right direction for reentry. It was a bit of a challenge.

ZIERLER: What were some of the environmental considerations to ensure that the spacecraft would not be harmed by radiation, by debris, by anything that would damage the mission?

BURNETT: [laugh] This is a sidelight, but the only thing that would damage it was a micrometeorite impact. All the data we had said that wasn't going to be an issue, but there were people at JPL, including one Caltech professor, who had done some models that predicted that the Genesis spacecraft was going to be destroyed in a matter of a year by micrometeorite impacts. We didn't believe them and convinced NASA they shouldn't worry about it. And nothing happened.

ZIERLER: To clarify, was it that an impact would not harm it, or that there wouldn't be an impact?

BURNETT: It wouldn't be something big enough to bust it all up. But there would be enough impacts to destroy some of the instruments or control features. And it was wrong. Because of the details of the crash, we don't have a lot of information on impact pits because not much of the spacecraft reentry capsule survived. We have found a few impacts over hundreds of square centimeters of material. So it was not an issue. Now, anything that would destroy the mission externally, environmentally, we couldn't see any problem. And there wasn't any. Whether we could do it ourselves or not, that's another matter.

ZIERLER: Was this purely an American mission? Was there an international component to it at all?

BURNETT: There were international PIs on the science team. We were offered a magnetometer from somewhere in Germany, but despite being free, we would've had to install it. And Lockheed Martin just decided it was too big an impact on what they were going to do, so that didn't happen. So everything was the United States in this case.

ZIERLER: As PI, what were some of your administrative responsibilities, and were there periods where you needed to focus your intention so intensively that your burdens of teaching at Caltech were lightened as a result?

BURNETT: I taught the same amount all through it. I didn't change anything. Whether I should've is another matter. Genesis was small enough that I followed everything technically. But our program manager, Chet Sasaki, handled all the management very well. All the main management, he did. We all got along very well with each other and worked very well as a team. Any management decisions, he made. I always agreed with him. But I tried to follow everything. So I was up at JPL two or three times a week. I made zillions of trips to Denver, which is where Lockheed Martin was.

ZIERLER: What about DC? Did you ever have to go there?

BURNETT: A couple of times. This was mainly at the time of launch and heading towards reentry. There were press conferences and things. But, other than that, no. Basically, the people who following it from DC would come to JPL for big monthly briefings, where they would review what we were doing and so forth.

ZIERLER: By the time you got to launch day, was the project pretty much on target, both in terms of the timing and the budget?

BURNETT: Yes. NASA gave us a few months' extra budget to allow us to postpone the launch window from March to August. But other than that, we were pretty close. We may have been a tad over, but not much.

ZIERLER: What was launch day like for you? August 8, 2001.

BURNETT: Oh, it was very exciting, but it didn't happen because it got deferred. There was some dust-up. The launch was delayed for a week because of some report coming out of Europe about some radiation damage effect on one of the control components. There had been some radiation damage tests done on a similar unit, and there had been a failure. Lockheed Martin and somebody else put together a big series of accelerated tests on our unit. These things were followed very closely. And we were being advised. Oh, boy. An old senior engineer at JPL, one of their old wise men, took me aside and said, "Stand by. This is not going to amount to anything. We'll just ride it out." And he was right. But unfortunately, the launch got delayed, so all the people who came down to see the launch basically had to go home." It was me, my wife, and a few other people who actually stayed around to see the real launch. It was delayed for eight days or so.

ZIERLER: Where were you? How close could you be to the rocket?

BURNETT: Pretty close. I remember watching from a close viewing point.

ZIERLER: Were you nervous that day?

BURNETT: Oh, yeah. This was one of the big moments. But that part of it went flawlessly.

ZIERLER: Of all the things that could go wrong, what were you most nervous about on launch day?

BURNETT: I didn't know. [laugh] There always had been launch failures with some component of the rocket and things like that. But we were using one of the small, well-tested rockets. We didn't need a great, big launch vehicle for our spacecraft. And then, all the deployment happened afterwards. There were a lot of details that happened once we got sort of in orbit, the boosters had dropped away, and the spacecraft was on its own and had to operate itself. This was always our concern.

ZIERLER: When you drop the boosters, is that when you know everything is OK?

BURNETT: Well, that's one good sign, when the boosters drop, and the spacecraft is zooming along fine.

ZIERLER: What is it like in terms of data analysis in real time? How do you know if Genesis is doing what it's designed to do?

BURNETT: Genesis was mechanism-rich, with a lot of moving parts. All these very high-purity materials were put inside a sample canister, which was designed and built by Don Sevilla, a mechanical engineer at JPL, and his team. This worked perfectly throughout the whole mission. It was basically a clamshell. Once you got into orbit, the lid of the reentry capsule, which was, itself, another big clamshell-like thing, opened up. It was pointed toward the sun. Then, the cover of our sample canister opened up, and we started to expose the materials. All these were brand new operations. Getting through launch and making sure it went OK was a major matter of concern right then. That was a key part of the mission.

ZIERLER: It's kind of a funny question, but did you ever think about what would've happened if the mission was delayed only a few more weeks, and September 11 happened? What would that have been like?

BURNETT: I never thought of that. [laugh] It would've been a big perturbation. It would've set it back umpteen months.

ZIERLER: Is your sense that September 11 messed up the scheduling going forward for subsequent missions?

BURNETT: I don't think so. I think that was just maybe a matter of luck on NASA's part. But no. I don't know that for sure because I was worried more about us than what other people were doing. But I think in general, NASA felt only minor effects from September 11.

ZIERLER: Was there a set understanding of how long Genesis would be in space?

BURNETT: Oh, yeah. We had a schedule for return. We were being brought back in September 2004. There was a schedule, which had been gone over many, many times.

ZIERLER: What were the determinations for making that schedule? Why that long?

BURNETT: It was, basically, how long we needed to collect enough solar wind to measure. We didn't want to make it too long because it would raise the cost of the mission. We wanted to be cost-competitive. But we wanted to make sure we had enough solar wind, so there was a compromise there. We figured two years would be adequate. They ended up giving us 27 months.

ZIERLER: Is part of that also redundancy? Are you looking to collect samples that you can compare against each other?

BURNETT: Yes. We had gone through all the things we wanted to measure. The highest priority ones were set. A major issue was the characterization of the materials purity; there was no way in the time we had to do this completely. We did as many as we could, but there was a time limitation there. We just couldn't get them all, so it was important to prioritize. We had planned redundant measurements for our most important measurements. The most important one was the isotopes of oxygen, then the isotopes of nitrogen.

ZIERLER: But what you're saying is, you knew that Genesis was successfully collecting samples before its return.

BURNETT: Oh, yeah. We had on the spacecraft solar wind monitoring instruments. This goes back to something driven by Marcia. There are three basic kinds of solar wind, three different mechanisms/regimes on the sun by which the plasma is emitted. And she said, "If you're going to do this right, you have to collect them separately." And we said, "Oh, no, no, no, it's going to be so much more complicated." "Yes, you've got to do it." And we did.

ZIERLER: Why? What's so important about collecting them separately?

BURNETT: The composition of these regimes was possibly going to be different. Let's back up. In terms of the basic science, we wanted to characterize these three different kinds of solar wind. We expected, and it turned out to be true, that they had somewhat different compositions due to fractionation processes. The basic material on the surface of the sun was all the same. But in the process of producing these different solar winds, it would fractionate them to varying degrees. And once I thought about it, I said, "This is great because we'll have samples that have been biased in different ways but have to come to the same source. If we measure the composition of these three different types of solar wind, apply the correction, and get the same answers, that's a verification that the answers are right." Eventually, I said, "Hey, I should be very happy we're doing this because it'll make our final data products much better."

ZIERLER: When the decision came that it was time for the spacecraft to return to earth, did you have any concerns, just to foreshadow to what happened? Was there any sense that it might not go as planned? What's the, "Houston, we have a problem," moment?

BURNETT: We had a major issue that came up at the last minute. February 2004, we had the Columbia reentry failure, where the whole Shuttle just came apart over Texas. Then, people at JPL started coming back and saying, "You guys don't realize what trouble you're in. You are now required to show that if your spacecraft came apart, nobody on the ground would've been hurt." The people who had modeled the breakup of the shuttle over Texas, said on average, it would kill three people on the ground in Texas. Now, it didn't happen. There's a certain standard deviation in this.

ZIERLER: Just random people that were in harm's way?

BURNETT: Yeah, debris that hits somebody's house or car, something like that. Now, these calculations are hard to make. They said, "You now have to prove that if your spacecraft came apart, it wouldn't hurt anybody." It was back to the drawing board. But JPL and our trajectory people led by Don Sweetnam, rose to the occasion. The more and more we looked at it, we couldn't have hurt anybody if we'd tried. We were coming in, and the debris, from the critical point, would've hit the most loosely populated place in the United States, someplace in northeast Nevada, where there's basically nobody. So the answer was, there was no way we could've ever hurt anybody if the thing came apart at the wrong time. But, it required a lot of work to show that.

ZIERLER: Why not just get rid of all of these concerns with an ocean landing?

BURNETT: Oh, it was infinitely more expensive. That was considered way back in the beginning. By re-entry time, we had all the facilities set in Utah to recover it. We were committed to that. And I think you'll see that the place where US sample return missions are brought back will be at Utah.

ZIERLER: What was that day like? Where were you when it returned?

BURNETT: In Utah, of course. That's a big story because we had a reentry failure. The parachute failed to open. I was sitting in the control room in one of the buildings next to the hangar where we were going to bring the craft back and dismantle the materials. We had set up a miniature clean room there to do this in a clean way, which turned out to be very prescient. People at JPL said, "You don't need to do this. We could put the whole thing up in a truck and carry it off to Houston. You don't need to do it in Utah." But we said we wanted to have some backup there, which turned out to be very, very critical because the thing did crash, and it all broke open.

That morning, I was sitting there, watching the thing come down, and it just didn't sound right. There was no statement about the parachute opening. It said it was now at 30,000 feet, and I just went to the next building because we had a contingency plan for who was going to go out to the crash site, and I was supposed to be on the team. So I headed over to the main building where all the Lockheed Martin people and some of the JPL people were gathered. And they came up to me and said, "Well, there are explosive devices aboard. We'd like to put one more person with expertise on the helicopter going out. Would you stand down and let this other person go?" And I said, "Yes."

ZIERLER: Was the parachute system off the shelf? Or was it specifically designed for Genesis?

BURNETT: It was specifically designed. But the crash was caused by the most minor mistakes possible, and they knew it within 24 hours.

ZIERLER: What were those mistakes?

BURNETT: It was an arrow drawn on one of the assembly drawings. The arrow should've been one way, but it was drawn the wrong way. It meant that the signal to release the parachute, which required a certain amount of gravitational force, pressure-dependent, was set to go the wrong way. And it was expecting a pressure decrease when it was a pressure increase. And that was it. The most minor possible mistake anybody could make. It's the kind of thing that in hours, and hours, and hours of review (which we had), you're never going to catch that this arrow was drawn the wrong way on this print.

People looked at the prints, but they were covering a lot of ground. It's just a very small mistake, which turned out to be very critical. The next morning Lockheed Martin said, "Well, we think we know what happened. It's this, this, and this." And my first question was, "What about Stardust?" Because it was done with the same thing. They said, "No, we looked at that. It's put in right for Stardust." Stardust launched ahead of ours, but their return was after. That was my main concern there, whether it would affect them as well. But they had done it right for them.

And then, my comment to the JPL people was, "Well, you're 99% sure why this happened. Don't spend $4 million to review and study why it happened to go to 99.9%." And so, in fact, they spent$4 million [laugh] to go from 99% to 99.9%. But I was right about the number. I pulled it out of the sky, but that was about what they spent.

ZIERLER: Before the disaster, in what ways was the landing designed to protect the samples, which I assume were quite fragile?

BURNETT: We wanted a midair parachute recovery. We didn't want the thing to have to parachute to the ground. We wanted it picked out of the air. We had some fairly sensitive materials to any kind of dirt or contamination, and we didn't want even a touchdown. And so, we arranged for it to be captured out of the air by helicopters. This was something that the Lockheed Martin people wanted to do. We were in accord there. It wasn't totally prohibitively expensive. It wasn't cheap, but it wasn't totally prohibitively expensive. The helicopter people, Lockheed Martin, and us had many rehearsals for this. We had it down. One of the sad things about the crash was it didn't give the parachute people a chance to show how good they were. They would've done it flawlessly. They really had it down. And they didn't get a chance to really pull it off. All the details were worked out. But they didn't get a chance to. The parachute never opened, so there was no parachute to catch.

ZIERLER: So essentially, Genesis crashed full-force into the ground.

BURNETT: Oh, yeah. Oh, boy, did it. It had a higher velocity than people had expected. I had some confidence that JPL's canister was built very strongly and could survive a good crash, but it broke all open. It was a big mess. A crash on the ground can't destroy the atoms from the sun. But, it can break up all the materials and put a lot of dirt on the surface of them. But beneath that dirt, the solar wind is still there. So you always had the hope that you could clean things up and recover. And that's what we ended up having to do.

ZIERLER: In terms of the stakes of the moment, just in terms of how you felt, as a proportion, what could you tell from remote analysis, and what were you waiting for, best case scenario, a safe landing to really study all of the samples?

BURNETT: The solar wind monitors, by the way, were Los Alamos built. I should mention that. They had recorded a lot of data on what types of solar wind, the proportions of the various kinds of solar wind, had been collected. That was very important. But the main science was dependent on analyzing the samples.

ZIERLER: Was the crash site dangerous initially?

BURNETT: No. Not really. [laugh] That was another issue. There was a certain amount of sulfur dioxide in some of the batteries, and there was concern of that being vented. But, this was in the middle of the Utah desert. And in fact, the first person from Lockheed Martin who got near–sulfur dioxide has a very strong odor, and he did smell a little bit of it, but the amount released was not much. I think he was chastised a little bit for going so close, but it really wasn't that dangerous.

ZIERLER: How much of a delay was it until you were able to get to the crash site?

BURNETT: Oh, I never got to the crash site until much later. The people from Lockheed Martin, helped by some of the people from JSC and the helicopter people, managed to get the sample return capsule back the same day. They picked up the whole canister. The canister was inside the return capsule. I think they must've had to take out the jumbled-up pieces of the canister. They put it in a big blue tarp and brought it back by helicopter, barely, because the helicopter was running out of gas, by 5 o'clock the same day. And then, they went out later and picked up all the rest of the return capsule. It was a very heroic effort on their part to get it back that same day. We were worried about water rising in the hole. In fact, it really wasn't much of a hole. The pictures look like the crumpled-up return capsule is dug into the ground. In fact, the sample return capsule just crumbled up and didn't penetrate the ground very much. The ground was very hard. And all the force went into breaking up materials in the return capsule.

ZIERLER: Emotionally, what were you feeling that day? Were you angry, sad, upset? Did you demand that heads should roll?

BURNETT: I wasn't upset. I was obviously concerned. I don't think I was angry or upset because I said, "OK, now, we have to work even harder." We figured if this happened, we could still, with work, get the material out. We just had to look at the pieces that were brought back into this hangar in Utah at the Test and Training Range (UTTR), at which the JSC people had set up the clean room. Which turned out to be incredibly important. It was derided by the engineers as overkill, but the JSC people and I prevailed. We essentially said, "We have to do this, and particularly if it there is any problem." It turned out to be incredibly important. So we were set up there with a clean room where we could look at the broken-up materials and recognize which is which from all the little fragments.

ZIERLER: Why is a clean room so important for analysis?

BURNETT: Well, it was to keep it from getting even more contaminated. We actually did not do much cleaning of the materials in there, but it was a nice, safe place with microscopes, tweezers, and various things to handle the broken fragments. And several of us spent a whole week , and the JSC people spent about a month, picking up the millimeter-sized pieces, piece by piece, out of the debris. And once you looked at them, you could recognize which piece went with the materials.

We had several different materials. You could learn to recognize them. There were three people who knew the materials that were at Utah. It was me, the number-two person in Genesis for years, starting about 1997 and going to the present time, Amy Jurewicz, now working out of Arizona State but at JPL at the time, and then Dorothy Woolum, who has worked with me from the 1970s on, even to the present time. We were all three there. It was sort of a celebratory thing. Amy and Dottie were there doing public relations, explaining about Genesis to various groups. But their presence turned out to be very valuable because we put them to work picking through the pieces, trying to package things up and take them safely back to JSC.

ZIERLER: When did you start to realize that not all was lost, that there were successful samples to analyze?

BURNETT: Oh, I never, ever thought that all was lost. I had all kinds of press interviews, and I said the same thing. "Stand back and give us a chance. Let's see how much of this we can recover." There were some experiments, which were very highly damaged, which we knew, and others, where we found some of the key samples had actually survived pretty well. There was a certain amount of luck when the crash occurred.

ZIERLER: If there was all of this care that went into a maximally soft landing, where you have a stage of parachutes and a helicopter rescue mid-air, all based on this concern that a successfully hard impact would damage the samples, how, at the end of this, when it's crashing full-force without any parachutes, are you saying to yourself, "I know I can extract a successful sample to study here"?

BURNETT: All I said to the press at that time was, "Give us a chance. Let's see what we can recover." Again, we knew that you could break up the materials, and boy, did they get broken up. And we knew they could get dirty, and boy, did they get dirty. But in principle, you could clean them off. And then, safely buried a very small amount beneath the surface is the solar wind, and it should be analyzable in principle. But that was in principle. We didn't know what we were going to get.

ZIERLER: What's the instrumentation? Are you basically working as a geologist here? Are you using microscopes? How are you determining what's spacecraft debris, what's Utah desert materials, and what are samples?

BURNETT: It actually wasn't a problem. You knew what things looked like. Amy Jurewicz was key there. She had actually made and processed a lot of the sample returns, spent a lot of time looking at them. She could recognize everything. She taught everybody how to recognize the various types of materials as little fragments. We all learned that very quickly. Then, it was just a matter of processing them, labeling them, putting them in vials. And what we decided very quickly the best way to handle samples was to use Post-Its. In fact, there's something called a clean room Post-It. You take this little fragment, and you stick it down on the Post-It glue, then you put the Post-It in some sort of Ziploc bag and label it. It took time to learn all these little details. Amy, Dottie, and I spent a whole week out there, and then the JSC people spent three more weeks finishing up the job, packaging it all, taking it down to the Johnson Space Center.

ZIERLER: Did you want to take samples back to Caltech?

BURNETT: I did. [laugh] But remember, I was never allowed to just take something to analyze. There originally was going to be an allocation committee. But Eileen Stansbery was the JSC lead there. I said, "Could I take a little bit of this back? I want four or five things here." And she picked those out and sent them to me.

ZIERLER: This is obviously going to be a difficult question, but what did you know you couldn't learn because of the crash?

BURNETT: We didn't concede anything. To this day, we haven't conceded anything. There are many important things we haven't done (yet). What's the main consequence of the crash? That we're still doing this today. It's just made a difficult experiment infinitely more difficult because we had to deal with the loss of the collected material and the contamination.

ZIERLER: Basically, that means the mission was a success is what you're saying.

BURNETT: Oh, yeah, we met our success criteria within a few years after that. All because of luck. The question had come up in the typical NASA way: "How do you define mission success?" "I don't know. I'm going to go and measure all these things." "Not good enough. Give us something specific you have to do." So we prioritized four measurements: the oxygen isotopes, the nitrogen isotopes, the noble gas abundances, and the noble gas fluences. And we were fortunate because we had a special instrument, the Concentrator, for doing the oxygen and nitrogen isotopes: an electrostatic mirror, built by Los Alamos and designed by Roger Wiens and Dan Reisenfeld, who's still working on Genesis at Los Alamos and others. It took the area of the solar wind from, let's say, 13 or 14 inches in diameter and concentrated it down to a few inches. In other words, the amount of atoms per square centimeter was 20 times higher. Because the solar wind is ionized, it was an electrostatic mirror. This instrument hadn't worked perfectly in flight, but it worked well enough. During the flight, we'd followed its performance. Fortunately, although the Concentrator came back a bit bent, 3 out of 4 target collectors, came back intact. The 4th was broken but we recovered a lot of the pieces. A little bit of dirt on them here and there, but they came back basically intact.

We had made enough progress by 2009 that we could say pretty confidently we were going to do all four of the Mission Success experiments. And in 2009, I think, the mission was declared a success. We didn't actually finish publishing the oxygen and N isotopes until about 2011, but we did meet all the criteria for the mission's success.

ZIERLER: Once you're now at this position where you've successfully analyzed the samples, what is surprising to you?

BURNETT: We had no idea what to expect for the oxygen isotopes. There were all kinds of proposals and speculations on what we were going to find. And there were some people who said that the way we were doing it, we wouldn't be able to see the differences between, say, the terrestrial oxygen isotope composition, that we wouldn't be able to measure accurately enough, that the concentrator could not do it accurately enough. It turned out that the oxygen isotope composition of the sun is very, very different from that on the earth and by an amount that was easily measurable.

And in terms of the systematics among meteoritic materials, it fit one prediction that the proportions of oxygen 18 to 16 in the sun was a lot lower than what you have on earth. The theory is "photochemical self-shielding". A major fraction of O in the early solar nebula is in the carbon monoxide (CO) molecule. Ultraviolet photons from the early Sun will "dissociate" the CO into C and O atoms. But the dissociation energy is different for CO with the different O isotopes. There is much more O16 than 17 or 18, so as the solar rays pass through a cloud in the solar nebula, the photons that dissociate CO16 get used up and deep in the cloud you only dissociate 17O and 18O, the atoms of which preferentially end up in water molecules which are incorporated into meteoritic materials which end up having a higher 18O/16O ratio than the original nebular composition (assumed solar). Our result fit in exactly with photochemical self shielding. The solar composition has a lot less O-18. At least qualitatively, predicting it quantitatively is more difficult.

That's probably been our most successful thing. That paper has been cited zillions and zillions of times. For nitrogen isotopes, we had some thoughts that they were going to be very different based on solar wind captured in lunar soils from the Apollo missions. But the lunar data there were very complicated. Basically, the Genesis data, by providing what the solar wind really is, clarified a lot of what people were seeing in these lunar samples, where there's a lot of variability in the nitrogen isotopic composition (still being studied today by Jack Schmitt of all people). It was very hard to understand. It all should've been from the solar wind, but it varied. We now understand very well. What you see in the moon from the lunar soils is a mixture of solar wind nitrogen and nitrogen coming in from various meteoritic impacts with different N isotopic compositions. Differences in the proportions of solar wind and meteoritic material explain all the variability. So those are our two most famous accomplishments. We've done a lot of other things.

ZIERLER: What theories or suppositions, going all the way back to Neugebauer, were confirmed as a result of Genesis?

BURNETT: Other than photochemical self shielding, the data on the different elemental ratios. Unlike various spacecraft measurements there probably is a difference between the solar wind and the sun in terms of the elemental ratios for low first ionization potential elements.

This is actually very important for planetary science because, taking the previous spacecraft data at face value, it said that elements which had a low first ionization potential, like iron, magnesium, sodium, potassium, calcium, aluminum, things like that, would not be fractionated. If we'd accepted this interpretation, we would've said, "What we measure is what you want." No correction. Well, it ain't that simple, because we could measure more precisely. And in fact--and we're still working on the exact details of this--there probably is some fractionation among these low first ionization potentials. Measuring these elements, the ratios aren't exactly what you want for the sun; there are corrections. We're zooming in on what those corrections have to be.

Beyond this, there is a large preferential depletion of elements which have the highest first ionization potential because they didn't get ionized. They stayed behind as neutral atoms on the sun. For an extreme case, let's say magnesium to helium. Magnesium is very easy to ionize and so was accelerated out of the sun in solar wind. Helium is very difficult to ionize, so some of the helium got left behind as neutral helium on the sun and didn't show up in the solar wind. This was supposed to be a factor of two or three. We basically confirm this, but there's more important complexity to it; see the next question.

ZIERLER: As a result of Genesis, what questions are now raised that weren't even possible before?

BURNETT: Well, like I said, if we can confirm that low first ionization potential element fractionation exists, it makes our interpretations harder, but we're after the truth here. Going forward, we also have prodded the development of better theories to explain low FIP element fractionation which constrain the processes of solar wind acceleration. That's feedback from what we have done to solar physics.

There is one other major outstanding question that we're circling, which is there's a big disagreement among solar physicists about the fraction of the heavier elements in terms of the structure of the sun. The basic issue is simple. Describe the composition of the Sun by three numbers: the mass fraction of hydrogen (X), the fraction of helium (Y), and the fraction of everything else (Z) with X + Y + Z =1. You deduce Z from solar spectroscopy. X and Y come from the seismic oscillations of the sun, helioseismology. The helioseismology Z = 1-X-Y disagrees with the directly measured Z from solar spectroscopy. Now, we are circling--it requires a lot more synthesis and maybe some better measurements of some elements--being able to say something about this major issue. I never even proposed this because I wasn't sure we could do it, but I now think there's a possibility now that by understanding these fractionation patterns among the elements involved here, hydrogen, carbon, nitrogen, oxygen, xenon, krypton, etc. that we can say which of these values for Z is correct,

We still can't do that yet. We could agree with either of them within errors right now. But we have a potential, I think, to do better. And that's a big thing that we have in mind.

{see also answer to question A, Page 26} In terms of direct comparisons with meteorites, this is a complicated issue. Basically, if you look up in a handbook what the composition of the sun is, i.e. the different proportion of elements, the data actually come from analyzing a rock that falls out of the sky. And this sounds incredible. You should be rolling your eyes at this. How does a rock falling out of the sky tell you something about the composition of the sun? It's a great bootstrap operation. The solar spectrum is full of absorption lines, and these can be identified with specific elements. It's a hard analysis, but you can calculate the composition of the sun from the intensities of these lines; however, error bars are large. So accepted solar composition is based on one kind of meteorite, which basically boils down to only two meteorites. that have fallen onto earth of this special type that have solar composition within errors with all the spectroscopic data that match it. Since the errors from measuring the meteorite are much smaller, people adopt these as the composition of the sun. It's consistent with, but doesn't prove that the meteoritic data are valid. They're precise, they're accurate from their analytical measurement, but that doesn't prove they're valid. Their validity can never be any better than the errors you have in the spectroscopic abundances. So we are starting to test the validity of the meteoritic abundances based on true solar data, namely from the solar wind. Long, complicated explanation.

For the data we have right now, the numbers actually agree within our errors and the meteoritic errors. They look pretty close. At least we will be able to say that within these errors, these data are valid compositions of the sun, which you never could say, independent of the larger errors on the spectroscopic data. Complicated thing, but this is a major issue. We were after this from the very beginning. In Genesis, you were required not just to see something, but to measure it quantitatively with error bars. And measuring with sufficient accuracy was always going to be a challenge, and with the contamination and the breaking up of materials, it's been an even bigger challenge. But we're getting there. It's taking a very long time, but we're getting there.

ZIERLER: How large is the community of researchers who are interested in and analyze these samples from Genesis?

BURNETT: A lot smaller than in the beginning. There are still a handful of dedicated people that are still doing it. We have an annual Genesis users group meeting associated with the Lunar Planetary Science Conference, which we did this year virtually, and it actually worked out fine that way. There are still, let's say, ten people working part-time on analyzing Genesis samples in the laboratories. It started with 20 or 30 in the very beginning. I have on problem with this, because everybody is gearing up to measure the new asteroidal samples from Hayabusa 2 and Osiris Rex. Amy and I will try to hold the fort with Genesis for the time being.

ZIERLER: What do you see as the successor missions to Genesis?

BURNETT: There are none. We said if we do it right, we won't have to do it again. Now, did we do it right? Maybe. I don't know. There are ways to do solar sample return better. But the best way actually is from a lunar base. Because there, you can have bigger arrays of material than we were able to put out, and you can have longer exposure times. You can get ten years with a square meter of collector if you want.

ZIERLER: This would require a manned mission, though?

BURNETT: No, it would require having a lunar base. This would not be justification for a lunar base., but if you were going to have a lunar base, then I've got a good experiment for you.

ZIERLER: There's a lot of excitement right now about building telescopes on the moon. Would this be part of that overall operation?

BURNETT: Could be. It would have to be on the side. It would have nothing to do with telescopes. It would have to be separately funded, but it would be a small fraction of the cost of going there and operating.

ZIERLER: And to be clear, this would require a manned mission. This is something that would have to be operational by human travel?

BURNETT: Yeah, there's no other way to do this. You'd have big versions of our arrays, and you'd go out and harvest these every now and then, bring them back on a service mission to the telescope.

ZIERLER: Obviously, all of this work is happening in the realm of basic science. Have there been any breakthroughs in applied science in what you've learned?

BURNETT: Oh, not really. We've extended and improved some of the analytical techniques considerably. We've helped people do better analyses on other types of materials. We've improved a lot of the quantitative aspects of secondary ion mass spectrometry in particular. But these are not major things. They're useful things. I wouldn't call them minor, but they're not major either.

ZIERLER: Back on planet earth, tell me about your considerations in going emeritus in 2006.

BURNETT: I did it for the money. Caltech has a golden parachute. We wanted to make an addition onto our house at Big Bear. And the amount of the golden parachute was comparable to the amount of the addition. Going emeritus didn't change what I could do. I could still write proposals. I did this in 2006, and until last year, I had an acting NASA proposal that whole time. I didn't have to serve on committees or teach courses, although I did volunteer to teach two courses that I thought needed to be taught. I still teach one of these at the present time. But it didn't change my life scientifically.

ZIERLER: But it's still been important to you to teach and remain connected.

BURNETT: Yeah. There was one class on cosmochemistry and the properties of meteorites, which I thought was important material that no one else was teaching at the time. Now, in the meantime, Francois Tissot has joined the faculty in the last couple years, and he's taken over that course. But then, I taught a course in nuclear chemistry, which no one would've ever taught and won't when I'm gone. I always argued that this material was useful, fundamental, practical, and of great historical importance. I teach it to this day every other year; did it spring 2021. I have three, four, five students. I think these people have learned something interesting and, I hope, useful.

ZIERLER: A bit of institutional history given your long tenure at Caltech. How has the division of geological and planetary sciences changed from when you first joined?

BURNETT: It changed a lot when I first joined. And it's changed a lot in the last few years after I left, mainly with the incorporation of all the environmental science work into our division. The big change at first was the introduction of planetary science. I came on the faculty in 1965, and Bob Sharp had decided to go into planetary science in the early 1960s. He hired Bruce Murray then Jim Westphal and Andy Ingersoll. Yuk Yung, and Dave Stevenson came along later. And that was a big change to broaden the scope of the division from just the earth to the rest of the solar system. The role of Bob Sharp in doing that was critical. He was a field geologist, a very good one, and a great teacher and person. I was near the beginning of this. Then, it basically stayed as the Division of geology, geochemistry, geophysics, and planetary science for years. In the last 20 years, it's started to move more into geobiology with Alex Sessions and Victoria Orphan in particular. But most of this happened as I was on my way out.

ZIERLER: I think for the last part of our talk, I'd like to ask a few broadly retrospective questions about your career, and then we'll end looking to the future. The first is quite broad, in fact. The power of extrapolation. How do you see your research and the things that you've discovered fitting into the broadest questions about how the universe works and what it's made of?

BURNETT: Well, we made a major contribution with the oxygen isotopes. And extrapolating it, I've got to live long enough to finish some of these other things that involve trying to refine our knowledge of solar elemental composition, not the isotopes. Also to try to make our inputs into these solar physics questions. This is not extrapolating real far; it's extrapolating five years or so. Beyond that, I don't know. It's very hard to predict. There still could be very interesting things to come out of further analysis of Genesis samples. The materials are sitting there, they're well-characterized. We know a lot about them. The Genesis Curatorial Facility headed by Judy Allton at the Johnson Space Center (JSC) has done a great job of cataloguing these things, knowing what they are and aren't, what they can and can't do.

Genesis material is like every sample return. The material is there. When you get new ideas, you can go back without a new mission to do it. That's the major advantage of sample return missions. It's been proven over and over again with the Apollo samples. Every few years, somebody says, "Hey, we can measure this now in the lunar sample." And we do it, and we learn a lot more about the moon and the solar system. So the long term value of sample returns is clear and unequivocal. And Genesis can do the same in ways that I can't predict.

ZIERLER: What contributions do you see your field making to questions like the origin of life on earth or prospects for astrobiology elsewhere?

BURNETT: In my field, the answer is none. Maybe that's a bit too strong. If you say my field is cosmochemistry, the study of meteorites and their relation to the composition and evolution of the solar system, one of the major elements, of course, is carbon. People in my field are in the middle of the characterization of the carbon properties of meteoritic materials and things like that. John Eiler's lab has made major contributions. This is very important to understanding the non-biological processes that produce various types of "organic molecules". Whether that's directly related to the origin of life? I don't think one has to appeal for any extraterrestrial origin of life. I think the possibilities for the process of forming life on earth are very likely. But this is not a field I know something about. So the basic answer is, if I define my field semi-narrowly, the answer is none.

ZIERLER: So much of your work with NASA and JPL came at what we might call the height of American power in the 20th century. What do you see as the prospects for ongoing American leadership in the field in the 21st century?

BURNETT: Cosmochemistry is and has been for the last 30 years, very international. The Meteoritical Society meeting is held all over the world, and there are strong participants from Europe, Australia, Japan, China, India. Any major country that does scientific research has people who work in cosmochemistry. The properties of meteorites are so varied, so complex, so interesting that they tend to invite the people who have the best analytical instruments to try out some of their instruments on meteorites to see what they find. Chondritic meteorites are the first materials to form in the solar system and have a unique record of the conditions there. So as long as there's a meteorite left–see, the wonderful thing about meteoritics, something could fall tomorrow that changes your life completely. It happened twice in 1969. Hasn't really happened since. But it could happen any day now. As long as there's scientific research, there will be cosmochemistry.

ZIERLER: By definition, the research you do is interdisciplinary. It covers many different distinct fields. If you look at your educational trajectory, the kinds of things that you studied as an undergraduate and as a graduate student, is that still the best course of approach for students, young people looking to get into the field now?

BURNETT: [laugh] That's a tough question. It worked fine for me. The opportunities now are not as great. My ability to move from chemistry, to physics, to astrophysics, to geology probably wouldn't be as easy today. Someone would be locked into their specialty more in their graduate work than I was at the time.

ZIERLER: Is that because all of these fields have matured?

BURNETT: Yes. But particularly, earth science has matured quite a bit. In our meetings at the Lunar Planetary Science Conferences, the astrophysicists present there. I say, "OK, you have a geological audience. Don't worry about them with equations. They are very mathematical, very quantitative. On the other hand, they may not know much physics. [laugh] Don't worry about your equations, but worry about assuming they understand something about physics because they may not." I've been away from graduate admissions for over ten years. The tendency, when I last was involved with it, was, people were very quantitative and had picked up what they needed to know from chemistry and physics within the context of geology courses. That worked OK for chemistry. I don't think it worked that well for physics. Now, the planetary science people are different. They're very physics-oriented. Many of them were physics majors and so forth. I think coming into geochemistry from something other than geology directly just isn't done much anymore. I wasn't unique in my history; a lot of other people did it that way. But I think it's fairly unique, and I don't think the science has suffered that much from it.

ZIERLER: What are some of the question marks that have been resolved from you going all the way back to the beginning of your research career? What's understood now that wasn't 40, 50 years ago?

BURNETT: A big thing to me is in the isotopic composition of the elements. Until 20 years ago, even though the different parts of the solar system were chemically different, they appeared to be isotopically homogeneous. Now, that requires a footnote. There are processes that are physical and chemical in nature that fractionate isotopes, and all of isotopic geochemistry is based on these, and these happen. They're very important to study. But the fundamental isotopic composition of, let's say, heavy elements, is pretty much the same throughout the whole solar system, yet we knew what was coming out of stars was isotopically wildly different one star to another theoretically, and later confirmed by pre-solar grains in meteorites. Stars produce elements of very different isotopic compositions. Yet, the solar system as a whole was isotopically very homogeneous. (An important caveat is that we only know this for the inner solar system.) Now, we know that there is a limit at--it varies with the element--a part in 10,000 to 100,000. These fundamental heterogeneities show that there's a limit to the homogeneity, although it's pretty good. A major issue is, why the approximate homogeneity? The prevailing view, I think, is that this reflects the fact that almost all materials that we now have been exposed to high temperatures, vaporized. Meteorites come from various places in the asteroid belt, some from Mars, and we have lunar material, but this is still a limited amount of material representing different parts of the solar system. The temperatures were high enough at one point that everything was vaporized and then mixed and homogenized isotopically.

Now, the 1 part in 10,000 isotopic variations is a big, big field. If you look hard enough, you'll begin to see that the different materials have slightly different isotopic compositions for elements like chromium, titanium, and so forth. And that tells you a lot about the inputs in the solar system from various kinds of stars. All of it's very complicated. That's been the big transition for me, just the evolution of isotopic geochemistry to find out where the limits of the homogeneity is. And then, we're back to the process of why it happened. High temperature is only the favorite theory. Alternatively, it's quite possible we inherited a lot of it, that it was homogenized before it came to us. But I think that's a minority view right now. But it's still an unsolved question sitting out there.

ZIERLER: What is it going to take to resolve those questions? Future missions? Better analysis?

BURNETT: Well, it would be nice to have materials from the outer solar system. That won't happen for a long time. It's just too difficult. Most importantly, we haven't really sampled the inner solar system. The recent sample returns from carbonaceous asteroids from Hayabusa and from OSIRIS-REx are important because these are materials that appear to have been processed a lot less. They may contain more fundamental inhomogeneities. So missions like these, robotic sample missions to well-chosen asteroids, can do a lot to shed light on this.

ZIERLER: An overall question in light of your career as a teacher. From undergraduates to post-docs, what have been some of the real values to your research in interacting with younger people in the field?

BURNETT: I haven't had a large number of graduate students, probably the order of ten, something like that. These are all wonderful people. I think we've always gotten along very well. I haven't kept in contact with all of them, but I think they were all happy with my time here. I never had much interaction with undergraduates except some in classes, to varying degrees of success there, actually. And with post-docs and people at the staff science level, I've had very close relationships over the years. What I was doing, it was always something fairly exotic and out of the way. So I never did get a lot of graduate students. Which is fine, no problem there. But you could have a very close relationship with post-docs. That was very important.

I also worked with students from other faculty members. I've collaborated a lot with people who worked for Ken Farley, where I think common issues of interest come along. And they've been very good students. I've had a lot of fun working with them. I was very close to Tom Tombrello, a distinguished pure and applied physicist, both in theory and experiment, who also was the chair of the division of physics. He died very suddenly a few years ago. I was very close to him, and worked very closely with some of his students in the 70s and 80s. So I've had a good time. Not necessarily doing things in the most conventional ways, but I've had a good time. And it's been a great pleasure working with people at Caltech.

ZIERLER: For those young scholars who are thinking about a research agenda that extends 10, 20 years into the future, what are some of the most exciting areas that you might say, "Focus on this," or, "Focus on that"?

BURNETT: That's a very good question. I've been so focused on Genesis, I haven't thought too broadly about that. What can be learned from meteorites is very profound and important, but also very challenging because they're very complex materials. And the study of meteorites will always yield interesting things. I think the business of looking at the small isotopic variations has sort of run its course. It's becoming very difficult to find anything new. Nevertheless, I'm sure there are never-ending useful things you can learn from the study of meteorites about what's out there in the asteroid belt, how it got that way, about the larger issues of how the solar system formed, the origin of the isotopic compositions of planetary atmospheres and so forth. It's all closely related to what you know from meteorites.

ZIERLER: Are there limitations in our technology and instrumentation that are obvious to you now, where we'll need advances in these areas to answer these questions?

BURNETT: I think people's ability to develop instruments will continue on. I'm not too worried about that. I'm just extrapolating from what's been a very successful increase in analytical capabilities. Very marvelous things. Just look at what John Eiler has done and the new things he has developed. It's been very spectacular stuff. Meteorites are great, but their main limitation is, they're giving you a totally random sample of the asteroid belt. The asteroid belt contain the first-formed materials in the solar system, thus it has a record of how the solar system formed. And you really need the spacecraft missions to do that. The best example is what's known from the fly-by orbital mission for the study of Ceres, the largest asteroid. Nothing has fallen to the earth that looks like Ceres. So for one reason or another, material from Ceres doesn't get to the earth. And that's just one example. Our limitations, would be overcome by more asteroid sample return missions, yielding a better understanding of really what's out there. Not that complicated and very profitable to study.

ZIERLER: Two final questions looking to the future. One is going to be purely speculative. Imagine a scenario where we could do a Genesis mission to our nearest star. We had the technological and budgetary capacities to do it. How would you design that mission, and what would be the most interesting questions you'd be looking to answer?

BURNETT: I'm going to throw cold water on this one. There's so much to study in our solar system. If the money and technology were available, I would spend it in our solar system. I may be a troglodyte, but I would take planetary science very literally. There is so much good stuff and so much to learn about our solar system. Better yet, we're now seeing solid bodies coming from other stars. Run out and sample one of those. Have something on standby to sample some of those. But I wouldn't go any further than that.

ZIERLER: Is that to say because you have a sneaking suspicion that the solar winds that you'd find from nearby stars would not be that different from what we have here?

BURNETT: Oh, it might be. But it's a matter of cost versus return. The cost to check that out would be so great, when you could take that money and do so many great things within our solar system.

ZIERLER: You mentioned that there are papers you hope to live long enough to write. What are those papers? What's left for you to accomplish?

BURNETT: It's all on Genesis, primarily. For years and years, I also worked with staff scientist Julie Paque back here at Caltech on the calcium-aluminum-rich inclusions from meteorites. These are literally the first materials to form in the solar system. I kept that going for a long time until the Genesis thing overwhelmed me (and more importantly, she retired). [laugh] Which is basically to say without her, I couldn't keep it up. And there are still some leftover things there I would actually like to go back and publish. However, realistically, there's so much that can be done on Genesis, as long as I keep raising a little money to do this, I will stay with this forever, as far as I'm concerned.

ZIERLER: Well, Don, I want to thank you so much for spending this time with me. It's been a great pleasure, and you've yielded so much historical insight and perspective. I'm so happy we were able to do this. So thank you so much.

BURNETT: You're quite welcome.

[End]