Episode 63: Dr. Aaron Burton on What Meteorites Can Teach Us About Life

Introduction to Episode

0:00Hi, you're listening to Let's Talk Chemistry, a podcast by Chemtalk. On today's episode, we interview Dr. Aaron Burton, a program scientist in the Planetary Science Division at NASA headquarters. Dr. Burton is passionate about investigating prebiotic chemistry and what can tell us about how life might have begun. He discusses his research on analyzing organic material in meteorites to better understand two big questions. How did life start on Earth and could it exist elsewhere?

0:31We hope you enjoy!

0:35Hey everyone! Welcome back to another episode of Let's Talk Chemistry. I'm Aaron, one of your co-hosts for this episode.

Origins of Life

0:42Today, we're going to be diving into the chemistry that explores the origins of life on Earth. Wow, what a powerful topic to discuss. As humans, we are so caught up in the day-to-day life that we don't pause and think, how did we get here? I'm Anya, and I'm excited to discuss the science behind this topic. And I'm Elizabeth. Chemistry really helps us uncover so much that was priorly unknown, such as how life started. Of course, we could not explore this topic without the help of a brilliant chemist who specializes in this area.

1:13We are joined today by Dr. Aaron Burton, a program scientist at NASA headquarters. Without further ado, let's welcome Dr. Burton and learn more about his background. Hi, I'm Dr. Aaron Burton. I'm a program scientist at NASA headquarters. This is a job I started recently after about a decade as a research scientist at the NASA Johnson Space Center. So I actually found chemistry a little bit late. I didn't enjoy it all that much in high school. And then I went on to a junior college in Oregon and had to take a lab science as part of my

1:44requirements from my associate's degree. And general chemistry fit better in my class schedule than physics or biology did. And so I ended up choosing chemistry. And I had a really wonderful instructor for that class. And we did a little bit more exciting labs than we did in high school. And so I started to really get excited about actually learning about chemistry and how things work and what some applications of it were. And then after I got my associate's degree from Clackamas Community College, I transferred to an in-state four-year school in Oregon, Portland State University. And there I had the chance to do not independent research, but NASA-funded research as an undergraduate

2:18student. And so that was where I got my bachelor's degree. And I was doing research in the lab that I really liked and enjoyed. And then I started thinking about, well, what do I want to do after this? That's why I was going to stick around and get a master's degree, also at Portland State. And I ended up liking it so much that I stayed on for a full PhD at Portland State University. I find it interesting that Dr. Burton did not have much interest in chemistry until he started college. I feel like society always says that you should have an innate passion for something to truly love it.

2:48But your interests can change and develop according to the environment around you. I totally agree. And I think Dr. Burton's experience emphasizes the role educators play in inspiring students. With interactive classes and passionate teachers, the results can be life-changing, as in the case of Dr. Burton. Yes. To think that taking one chemistry class in college can lead to a job as a NASA scientist is incredible. Speaking of his work with NASA, I noticed that Dr. Burton started working with NASA quite early

3:19into his educational journey as part of his bachelor's degree. I wonder if this prompted his current role as a program scientist there. Let's hear what he has to say about this.

Dr Burton's Research Background

3:27I think I didn't have a really good vision. I didn't really see myself working at NASA. But the research I started working on as an undergrad was on looking at molecular evolution of DNA and RNA. And so we were studying RNA enzymes that we could evolve in the lab to try and add new functions, which is related to potentially the origins of life. And so working a lot of that prebiotic chemistry was really interesting to me. And then the research lab I was working in had funding from NASA to do that sort of work. And so that was a chance to do research that I was interested in that also overlapped with

4:01NASA's mandate. And so that was just a good synergy there. And so after I left grad school, I actually was looking to do a postdoc somewhere. And so I applied to do a postdoc at the NASA Goddard Space Flight Center in Maryland. And that was where I started studying meteorite samples, looking for amino acids and other molecules made out in space that we would characterize in the lab. Again, addressing that bigger question of, you know, how did life start? What does prebiotic or abiotic chemistry look like? And, you know, could there be life elsewhere?

4:32Wow. Not only did Dr. Burton's research help him get his foot in the door with NASA, but his work on molecular evolution and meteorite samples seems to tie into some of his work today. That's true, Aaron. Most of Dr. Burton's current research revolves around space and astromaterials. But what does this help scientists do? Let's have Dr. Burton explain the focus of his work and the purpose behind it.

Understanding Life on Earth

4:58So the overarching question I'm interested in is understanding how life started on Earth and whether it could exist elsewhere. One of the challenges to studying this is that on the current Earth, we have biology basically everywhere and a lot of geologic processes going on that have erased a lot of the historical records. And so, you know, if you could invent a time machine and travel back right to where life was starting, you could go grab a sample and then we could figure out exactly how life started. At least currently, we can't do that. Maybe you could argue it'd be a bad idea if we did, because then the butterfly effect,

5:28you would change how everything went down. But, you know, we don't have real good samples of how things were on the early Earth and how life might have started. So that's where meteorites come in. So meteorites are the surviving fragments of asteroids and potentially comets or other planetary bodies that survive passing through the Earth's atmosphere and where there are meteors. And then the piece that ends up on the ground afterward is the meteorite. And so even though that sounds like kind of a violent process, a lot of the material survives and the very outside edge of it gets burned or maybe you get a little bit of a

6:02shock fragmentation. But most of the material remains intact. Most of the material that survives remains intact and not too heavily altered from that atmospheric process. And so some of the meteorite samples that we have contain rocks that are, you know, basically forming at the same time as the solar system. So four and a half billion years ago. So this meteorite that we can get in the lab is sort of a time capsule for what was happening four and a half billion years ago. Interesting. Dr. Burton's right. Unfortunately, we don't live in a back to the future type world and we don't have a

6:34time machine to travel four and a half billion years ago and figure out how life started. But it seems to me that chemists like Dr. Burton solved this problem by acting as a kind of scientific detective. That's a good analogy, Elizabeth. Yes, Dr. Burton and his team examine meteorites the same way that detectives investigate the scene of a crime. Both reveal clues that help us decipher what happened. But we can't simply look at a meteorite and expect to learn something. Much like how detectives run fingerprint tests to determine possible suspects of a crime,

7:06scientists use sophisticated processes to obtain the chemical information held within a meteorite. Let's hear from our expert on this. So the best days in the lab are the ones where we're analyzing new meteorites. And so that involves taking, you know, a sample of a meteorite, we crush it up into a powder, and then you're putting it in a test tube and doing an extraction and some sort of solvent. So for a lot of compounds like amino acids, they're polar and water soluble. So we would do a hot water extraction of water. So you're doing 24-hour reflux at 100 degrees C, and then you extract that solvent.

7:38And then for amino acids in particular, some of them end up as free amino acids after that extraction, but typically about half are bound in some precursor form. So whether that's a nitrile or part of some sort of, I don't want to say peptide, but not a biological peptide, but if there were two amino acids leaked together or some other precursor or acid labile molecule that you can turn into amino acid. So we'll do an acid vapor hydrolysis. So you put your test tube with your dried extract in a larger test tube, and then add

8:08six molar hydrochloric acid to the outside, and then do an acid vapor hydrolysis. And then to remove things that don't interfere with the analysis, we do cation exchange chromatography, which allows us to get a fairly pure amino acid extract out of that. And then we analyze that by liquid chromatography mass spectrometry or gas chromatography mass spectrometry to be able to do compound-specific measurements. That certainly sounds like a complex process. It almost reminds me of making tea. The sample is crushed just as how you break up the tea leaves.

8:40Hot water extraction dissolves water-soluble compounds as hot water releases tea flavors. Acid vapor helps release stubborn compounds, similar to squeezing out all the tea essence. Finally, chromatography filters impurities, like putting tea through a strainer to make it smoother. I like the comparison, Anya. If only analyzing a meteorite sample was as easy as brewing a cup of tea. The truth is, we need advanced scientific equipment to help us perform the analysis and take measurements, as Dr. Burton described.

9:11But what if you want to obtain a sample from another planet? Do we use more specialized equipment for that? I was wondering about that too. Let's hear from Dr. Burton about this case. Just with standard, commercially available mass spectrometers and chromatography instruments, we're able to benefit from the investments that industry and various organizations on Earth have put into building these really advanced instruments. And so we don't have to do so much of the inventing on that. If you want to send this instrument on a robot to another planet, that's where you have

9:43to do more of the, how do I shrink this mass spectrometer down? And if I can't put a massive 600-pound instrument onto a rover, so what are the most important functions of that instrument? What compromises can I make? But so like Curiosity Rover on Mars has pyrolysis, GCMS on it. So we're able to do chromatography, mass spectrometry on a different planetary surface, which is just incredible to me anyway. But we haven't been able to do the extraction parts yet because it's hard to bring solvents and manipulate them and not have clogs. Interesting. So it sounds like using equipment for other planets is more so about adapting

10:18existing technology to make it more compact than actually inventing new equipment. It was also so cool to hear about the Curiosity Rover on Mars and its ability to do planetary analysis with a spectrometer. We're doing science experiments on other planets. It sounds to me like we're living in the future. I totally agree, Aaron. I hope that as our knowledge of space and planets develops, we can develop a way to take extractions on other planets. Though I'm sure performing chemical experiments on any planetary object comes with an enormous set of challenges.

10:53Let's listen to some of the precautions Dr. Burden and his team takes when analyzing meteorite samples. It's sort of our going-in assumption when we look at things like meteorites. So most of our meteorites are recovered, not as observed falls. So it's not like you see the meteor come in and then you're like, oh, it landed in this area. Let's go recover it. But even in that case, it has experienced time passing through the atmosphere. It's landed on the ground. It's been sitting on the ground for some period of time. A lot of our meteorites come from Antarctica, where they may have been there for 100 or 1,000 or 10,000 years sitting in the ice until they get

11:27covered. But so we always sort of assume that what we're seeing is contamination until we have convincing evidence otherwise. And so for amino acids, that looks like abiotic chemistry should have racemic amino acids, especially for the ones that are found in proteins. And then we want to find amino acids that are beyond the ones that biology normally uses. And so there we try just to do no more harm than has already been done by Earth's environment. But some of the materials that we bring back from missions, so like OSIRIS-REx just returned last September, and that grabbed material directly from an asteroid. So that's something that would be a meteorite, but it passed through

12:02our atmosphere within a sample return container. And so there we have the history and contamination, our sort of custody chain of everything that went into making that capsule. We know how clean it was when we sent it. And so there we have a pretty good baseline of what contamination we could have introduced. And then we try to curate it under as best conditions as possible. So clean room, constantly flowing nitrogen to just minimize, hopefully, any additional contamination that we might add. Wow, I never knew contamination played such a big role in the accuracy of scientific experiments.

12:35So all the precautions taken by Dr. Burton and his team feel very necessary. If a contamination led them to make a shocking discovery, they would be spreading misinformation in the scientific community. That sounds catastrophic, but inaccurate discoveries due to contamination have been made before. In 2005, the paleontologist Mary Schweitzer claimed to find intact blood cells in a 70-million-year-old dinosaur fossil. This discovery shocked and awed the scientific community, but was later faced with

13:05scrutiny due to concerns over contamination from modern bacteria. This raised questions about whether the observed structures were genuinely ancient or simply a result of modern organisms. That's so intriguing. Thank goodness Dr. Burton has a methodical system worked out with his team to avoid contamination. In general, it seems like Dr. Burton does a lot of work with others to ensure that NASA is making good scientific progress. Absolutely. Working with a team means others can spot errors you might overlook, and you can do the same for them.

13:38This way, the final result is much more precise and accurate. In addition, other people would specialize in areas that you are less familiar with, so collaborating with others would enable all of you to learn from each other and recognize different solutions or possibilities. This is especially true at places like NASA, where scientists often specialize in specific areas such as types of planets, like rocky or gas giants, comets, asteroids, and other small bodies, processes like volcanism, and more. By combining all their knowledge and expertise together,

14:11scientists like Dr. Burton can work together to create a galaxy of insights, each element adding to the collective understanding. Here's more from him. I think one of the most important things that you learn is that if you're going to do something like put an instrument on a rover, there's a whole team of people that know things that you can't possibly know, and likewise, we just all can't have enough expertise. And there's always sort of this tension between the scientists and the engineers. And so it's really important, actually, that you work together. There's a whole lot of challenges. So even beyond just chemistry or your scientific

14:46discipline, there are a lot of engineering aspects that I'm not an expert in, and so then you team up with people who are experts in it. Exploring Mars, you know, I have a lot of background in prebiotic chemistry and organics and meteorites, but then we team up with people that are experts on Mars geology and Mars geochemistry so that all of you working together can help interpret the data that's coming out of the mission. Another advantage of working in a team is that you can discuss challenges and identify underlying reasons behind a situation. For example, as mentioned earlier,

15:17the possibility of contamination is a major concern and challenge in this field. Scientists must avoid making hasty conclusions about intriguing findings until thorough research has been conducted to better understand the situation. Actually, Dr. Burden also discussed this challenge of accounting for possible contamination in order to ensure accurate results. So let's hear his perspective. There's a temptation when you find something really interesting. Like if I find all L amino acids in a sample, you're like, oh, this is how homochirality started or why biology only uses L amino acids. But then

15:53you're like, well, it's most likely that this is actually bacteria growing on this and I've extracted bacterial cells. So it's really being kind of the biggest skeptic of your own work. I think it can be a challenge once you start getting excited and you start, you know, you're writing the paper in your head about what this finding or that finding means and really just making sure that all the data lines up and you've done all the checks necessary to make sure that what you're seeing is real. Oh yeah. Collaboration and peer review would definitely help you make sure you're not jumping to incorrect conclusions and feel more assured in your work. For sure. Dr. Burden has been conducting

16:27research for the past 21 years, so he's had the opportunity to work with numerous groups on a variety of research projects. One project he's excited about is what the samples from the OSIRIS-REx reveal as they get analyzed. OSIRIS-REx is the first U.S. asteroid sample collection mission. In September 2016, the spacecraft was launched to an asteroid near Earth called Bennu. After reaching the asteroid in 2018, OSIRIS-REx spent almost two years orbiting, mapping, and studying Bennu before

17:00collecting a sample of rocks and dust from the asteroid's surface in October 2020. Almost three years later, the spacecraft delivered the sample to Earth in September 2023. That's so cool. As a matter of fact, some of the initial findings from that mission are now available and can be found on the NASA website in the article, Surprising Phosphate Finding in NASA's OSIRIS-REx Asteroid Sample. Another project Dr. Burden worked on is flying a miniature nanopore DNA sequencer demonstration to the International Space

17:32Station. Here's more from him. And so we were able to do a technology demonstration that this commercial DNA sequencer that's like the size of a Snickers bar, it has these little nanopores in them, and as the DNA or RNA strand passes through it, you get a change in current that is diagnostic of the base that's passing through it. So A, G, C, or T. And so that gives you a way of sequencing things. So we were able to get that to work, and we got to work a little bit with the astronaut who first did the experiment, Kate Rubins. So we got to kind of design crew procedures. And that, for me, was a fun

18:03experience because one of the things I really like about planetary science and the work that I'm doing now is a lot of the things that we assume are sort of constant or universal. So like, you know, water freezes at zero degrees Celsius or 32 degrees Fahrenheit. It boils at 100 degrees Celsius or 212 degrees Fahrenheit. Well, that's true when there's one atmosphere of pressure, right? And so if you try to make spaghetti or macaroni and cheese in Denver, right, the boiling point of water is actually lower because the atmospheric pressure is lower. Gravity is 9.8 meters per second on Earth,

18:35but not on Mars. And in the case of the International Space Station, that's microgravity. So you have to think about little things like, can a pipette work in space? Is surface tension enough to, you know, allow it to work normally? Or do you need some special device to remove air bubbles? So that project was really fun. And I'm hopeful that in the future, we'll be able to actually send some sort of sequencing technology to Mars, you know, to look for DNA or other, possibly other evidence of, of life. Wow. I never really thought that things like the boiling or freezing points of a liquid

19:11would change depending on where you are. I always thought of them as just facts that are always true. Me too. It's pretty interesting how even on Earth, those differences are noticeable. As Dr. Burton mentioned, in Denver, Colorado, the boiling point of water is 202 to 203 degrees Fahrenheit. But in a lot of other places, it's about 212 degrees Fahrenheit due to variances in atmospheric pressures. And for nanopore DNA sequencing, variations in atmospheric pressure can cause the DNA to move too quickly, too slowly, or inconsistently through the nanopore, leading

19:42to different readings. That's interesting. Scientists would probably have to make some major modifications to the device for nanopore DNA sequencing to work on other planets, like Mars. Definitely. And considering how different Mars is from Earth, if life exists over there, their DNA likely works differently than DNA here. And other signs of life would vary too. I agree. That makes the possibility of sending sequencing technology to Mars in the future so fascinating. Imagine all the differences it might find. It could revolutionize our understanding of

20:14what life is. Absolutely. While this potential future project is certainly intriguing, it's important for scientists to remember to take breaks. I'm curious, when Dr. Burton kicks back to watch a sci-fi film, how does his work affect his perception of these futuristic stories? Does he think that lightsabers, time travel, and alternate universes are all made up? From Jedis to the USS Enterprise, let's take a step back from the lab and imagine what it's like being a NASA scientist on their day off at the movies watching sci-fi films. Let's hear from Dr. Burton.

Science in Science Fiction

20:48So that's a tough question. I watched the movie for enjoyment and I tried to suspend, you know, set aside my real scientific mind while watching some of these movies. I think it was Spider-Man 2 or Spider-Man 3 where they had, it was tritium and it was like this glowing orange sphere that kind of looked like a soccer ball. And it was like enough tritium to blow up all of New York City or something. I remember just laughing about that because I was like, well, I don't, I haven't worked with tritium directly, but I don't think it's a glowing orange ball of gas, you know, that you could manipulate. I like some of the things that, you know, challenge, again, I guess, sort of our

21:21perspective, but I really liked gravity and the idea that time passes differently depending on where the solar system or where in the universe you might be. Because I think that we, that's another thing. A year is 365 days on Earth. A day is 24 hours. So even just getting to Mars, you know, a day is, I think about 40 minutes longer. And so Mars time and Earth time go asynchronously. So if you're working on the Mars mission, a lot of times when you first start the project, you work on what's called Mars time. And so your day shifts by about 40 minutes each day. And so after two weeks, your

21:56day and night are completely reversed. So maybe that wasn't the perfect answer to the question. I like movies in general and books that, you know, really hammer home that fact of how, how ingrained we are in, oh, this is how things are on Earth, but it's really not, not that way everywhere. Dr. Burton seems to take it all in good humor. And I'm glad he can still find enjoyment watching his friendly neighborhood Spider-Man, even when it's not factual all the time. Yes, he even acknowledges that science fiction challenges us to reconsider what we take for granted, like time and gravity. Perhaps these imaginative stories, though not completely realistic,

22:32can serve a purpose by inspiring us to test the limits of what is truly possible. Agreed. Science fiction could also help the audience to be excited about STEM and embrace their imagination and curiosity. Although science fiction may spark ideas, Dr. Burton knows that making discoveries requires more than just imagination. For the future Tony Starks and Bruce Banners who dream of following in his footsteps, Dr. Burton has invaluable advice. I think for me, one of the biggest things that I learned, I would say even in general chemistry,

23:03was just the breadth of what chemistry is and what being a chemist is. And so you go all the way from learning what about electron distributions and the S orbitals and the P orbitals, and then you do electrochemistry and then you do biochemistry. And so if you like chemistry, find the part of it that you really like, you really love. For me, it was biochemistry. Like I loved knowing how enzymes work, why you need certain vitamins, why you need just all the things like that are what really spoke to me

23:35and what I was passionate about. And so having that, I was able to jump into the research part of the career where, you know, I was like, I get paid to do scientific experiments, which is cool. Like I think about this stuff for free, you know, at home or after hours. And so to be able to have that be my career is great. And so just find that part of it that you're really interested in. And there might be parts that you don't enjoy as much. If math is not something that you love, then maybe physical chemistry isn't exactly where you want to go. Or maybe you don't like being in the lab. So there,

24:08you know, there's computational chemistry, there's all kinds of chemistry is such a broad field that if you can find the part of it that you like and that you enjoy, then try to follow that passion. Thank you, Dr. Burton, for sharing your stories and wisdom with us. We have such a blast. And to our listeners, the mystery of space to infinity and beyond await. Until next time, which as we learn differs depending on where in the universe you are. Bye. Thank you for listening to Let's Talk Chemistry, a podcast by Chemtalk. We hope you enjoyed it.

24:45For more information on today's episode and countless chemistry resources, please visit our website at www.chemistrytalk.org.