'It’s Like Being an Archaeologist But for the Solar System'

Maximilien Verdier-Paoletti holds a meteoritic sample inside his office at Carnegie's Broad Branch Road Campus. Photo: Roberto Molar Candanosa, Carnegie DTM.
Wednesday, July 10, 2019 


Scientists consider stony meteorites known as chondrites to be the archives of the Solar System. These space rocks are fragments of primitive asteroids. Even though most chondrites undergo some rough travels before landing on Earth, they are still a major source of information about the conditions of the material surrounding our star when it formed billions of years ago.

To study grains preserved in chondrites, scientists destroy and slice pieces of meteorites in the lab. In this Postdoc Spotlight, Maximilien Verdier-Paoletti talks about the nuts and bolts of doing this cosmochemical analysis and how he became what could be compared to an archaeologist—but for the Solar System.

DTM: What do you do exactly?

Max Verdier-Paoletti: Basically I’m looking at very tiny dust inside what we would call primitive meteorites. Since they formed at the birth of the Solar System, they practically stayed the same. Looking at those is like looking at the past and how and where the Solar System formed.

Within those meteorites we can find very tiny dust, 10 times to 100 times smaller than hair, so invisible to the naked eye. The particularity of those is that they form in dying stars before the Solar System itself. So when you get a big star that’s ending its life, in an explosion for instance, giving a supernovae, it can create some very tiny dust, at the nanometer scale, and we can find these inside meteorites. Also when a star ends its life, not in an explosion but like our Sun would, becoming a red giant star, it can produce those too. And that can also be retrieved from these meteorites. Looking at this dust is like looking at the inside of those stars, and at the same time at how the galaxy evolved.

DTM: So you are a cosmochemist?

MVP: Before my postdoc I would’ve said I am a cosmochemist, because that would basically mean I study meteorites. That would be it for me. But since I got here, I am still studying meteorites, but to understand stars. Stars are more in the field of astrophysics. It’s hard to put a clear boundary on what I’m doing. Since everything I’m doing on meteorites is to understand stars and the galaxy a little bit better, it’s really a blurry boundary between the two.

DTM: Do you have an ultimate, overarching goal you are contributing to?

MVP: From the point of a cosmochemist, I want to understand the Solar System and how it formed and how the Earth formed. To a larger extent, cosmochemists want to understand the origin of water and life on Earth. From an astrophysicist point of view, it would be to understand how stars and galaxies and other objects in the universe might form, die, and contribute to the formation of Solar System-like objects.

Maximilien Verdier-Paoletti joined DTM's cosmochemistry group in January 2018. Photo: Roberto Molar Candanosa, Carnegie DTM.

DTM: In your perspective, what does the early Solar System formation look like, and what other fields do you have to work with to constrain that idea that you have of it?

MVP: The beginning would be just a region filled with dust and gas. That would be it. Something happens inside this that led to the formation of a star and the formation of a disk of gas and dust around the stars, which led to the formation of planets. How it is inside all of this? It’s a very good question. Depending on where you are, it would be very hot or very cold, very dense or very light. It would be a mess basically. A real mess. But that would lead to the very ordered Solar System.

It’s very complicated to say what scientific fields we need to answer those questions—almost all of them. You need chemistry. You need physics. You need biology. You need geology and geochemistry to look at isotopes and use those as clues to answer our different questions. You also need astrophysics because the stars in the environment of the nascent Solar System will influence its formation. You basically need everything. Cosmochemistry for me is in between geology and astrophysics using both of their tools with geochemistry

DTM: Were you contemplating all of these interdisciplinary implications before? Did your research focus change before coming to Carnegie?

MVP: My focus was broadened when I came to Carnegie because my PhD subject was very different. The link with my PhD is very small: meteorites. But what I was looking at before is very different from what I look at now. I had to acquire new scientific tools and grasp a completely new vision on what I’m doing. It’s great because in the end you are learning a lot. It’s funny because I remember when I started to look at the project here, I thought, “Oh, it’s everything that I don’t understand. Things that I’ve seen in conferences that are way too complicated for me.” But it turned out okay! I took the time to learn and I feel that I’ve opened to something that seemed out of my reach before. I think it’s great choosing a postdoc that is not very close to what you did during your PhD—that it’s linked by something, like the objects or instruments you are using—but that’s something completely different to open your mind.

DTM: How did your focus change?

MVP: I was studying asteroids and looking at how the water inside them interacted with the rock, changing the minerals and how and when the water moved inside these asteroids. Now I’m looking at presolar dust. I’m studying stars, how they contributed to the Solar System formation and how  they die and form new elements.

DTM: Why were you interested in this water?

MVP: It’s important because we know asteroids might have brought some water to Earth in the beginning. I was telling you some of these asteroids and meteorites are primitive, and they did not change a lot. Looking at those asteroids is like looking at the archives of the of the Solar System. It’s like being an archaeologist but for the Solar System. As if you were going in the field and someone started to displace and break bones. The water is basically doing this. By changing the asteroid, it’s hard to retrieve information about the Solar System formation that we could find by looking at the initial minerals. Understanding how the water flowed in those asteroids and how it changed them might enable us to retrieve this initial information that might still be retained in the asteroids. That’s the idea.

DTM: What kind of objects do you work with to do your research?

MVP: Basically we do two different things. The first is to find the preserved grains. Sometimes we take a meteorite and destroy it. We use a bunch of different acids on it and dissolve it completely because we know that in the end, what will remain, what will resist to those acid attacks, are the presolar grains. Someone in 1970 said it’s like burning the haystack to find the needle. Sometimes we can do this and get at those grains.

But other times we don’t want to do that, because dissolving the meteorite will dissolve another type of these presolar grains that are less resilient to acids. So we take a section of a meteorite and put it inside the NanoSIMS to make maps of specific isotopes. This is because we know those grains will have isotopic compositions extremely different from what we can measure in the Solar System. It’s as if you were looking for something in the dark that strongly reflects light. So you pass a light over the section  until something flashes back at you. When we are looking for these grains we are basically looking for something that’s giving you a big signal, so when you do the maps you sometimes see a big hotspot, and you know this might be a preserved presolar grain.

Secondary electrons image of a presolar silicon carbide. Those grains are highly resilient to acid attacks. As a consequence, they are part of the remaining fraction of material left after the dissolution of a chunk of a chondrite. Image courtesy Maximilien Verdier-Paoletti.

DTM: Tell me about the types of meteorites you use in your experiments.

MVP: I use meteorites we call chondrites. They got their name from the chondrules within them, which are balls of molten rock that crystalized inside the vacuum of space during the formation of the Solar System.

Two main types of meteorites exist, the differentiated ones that comes from asteroids that completely melted and acquired an earth-like structure, meaning an iron core surrounding by a rocky mantle and a rocky crust. Because of the melting process no presolar grains can be retrieved from those. Chondrites on the other hand preserved their primary structure. They often look like a block of sand or of dry mud in some cases, specifically the carbonaceous chondrites. But they have the great interest of being relicts of the planet formation, so they still contain the primary constituent of planets that you could find at the beginning of the Solar System formation. Because of their primitive nature, we know presolar grains are sufficiently preserved within those meteorites.

DTM: So, who do you work with to do all of these measurements?

MVP: My main collaborator here is Larry Nittler. He’s helped me a lot. In the beginning he spent two weeks with me in front of the instrument to teach me how it works. I was asking him tons of questions because in the beginning I was learning about the subjects. As the fellowship progressed, I became way more autonomous.

Jianhua Wang is also constantly helping me a lot when I’m working with the instrument. Both of them must be tired of me because almost every time I get on the instrument a problem arises. It’s like I’m jinxed!

DTM: What would you say are your most significant contributions so far?

MVP: We soon might have some new information that can shed light on how the galaxy evolved chemically and how an under-considered type of star might have contributed to this evolution.

We have another project involving rare earth elements in presolar grains using a new instrument that offers an accuracy never reached before. But I had a bunch of bad luck doing this! For instance, I was preparing to do these measurements for over three months. I isolated tiny grains with Conel Alexander, did some measurements to characterize them, and while trying to put the sample in a holder, it slipped. I caught it with my hands wearing gloves, but my thumb touched the surface and got rid of all the grains. So we could not conduct the measurements because all the preliminary work was destroyed within a second. But that’s science too! Sometimes you are lucky, sometimes you are not.

Chemical map of the pristine carbonaceous chondrite Acfer094. Numerous Chondrules can be distinguished along other phases, such as metal (red). In between those constituents is the primitive matrix in which presolar grains can be found. Image courtesy Maximilien Verdier-Paoletti.

DTM: What’s the most exciting thing about your research?

MVP: It’s two things. It’s a field where basically your job is to learn. You are learning the way you want. Not following lessons or things like that. You are reading a lot, learning all the time. This brings you a certain humility because the more you learn the more you discover that you know nothing. You are in this constant state where you question everything. Then there’s also the thrill I get from knowing that I am getting closer and closer to understanding something that no one has ever understood before.

DTM: What other things are exciting?

MVP: I find quantum physics fascinating because when people started to discover and understand this, they basically saw that all the rules they thought were controlling and shaping the universe can’t apply at the quantum scale, that it was something completely different that we could not explain with the knowledge we had. We gathered knowledge over centuries, and we had this feeling of understanding the universe better and better. But then, a lot of theories emerged, such as the black-body radiation of Max Planck and the photoelectric effect of Albert Einstein, that shed light on the structure of matter at small scale and how energy in different forms interact with it. This was a starting point. The more the scientific community learned of all of this, the more they understood the complexity of matter at the subatomic scale and the laws acting in this weird, inaccessible at the time, world. Nothing was behaving as it should according to classical physics. And today we know that quantum mechanics explains a lot of subatomic phenomena that play a major role in the life of stars and can account for the birth of black holes, for instance. I love this. This smallest scale phenomena explaining the largest objects in the universe. I find the contrast extremely fascinating.

DTM: What about other things on Earth that are exciting?

MVP: I think for me it’s things like sociology—trying to understand hidden patterns that are governing human interactions and how we built societies. We have the feeling that we are in control, and we do things because we want. But very often I think there’s an illusion of choice. So yeah, the human nature itself is really interesting.

DTM: What would you say are the major challenges in the scientific community?

MVP: In science I think the most important thing is to overcome egos. It might be weird as an answer but actually it makes a lot of sense when you’ve been in different labs or attended conferences and can see that sometimes interacting with other scientists can be very difficult. Sometimes people are not as reachable as you would expect them to be. You tend to have this vision of scientists being extremely intelligent people, and that intelligent people would do intelligent things. But sometimes it’s not at all like this. People can be isolated and interacting with them can be tricky.

Doing science without collaboration maybe made sense two centuries ago, but I have this feeling —and I might be completely wrong—that we are reaching a stage in science where we have to understand very, very complex processes and things about life, the universe, and Earth that rely on very different aspects of science that a single person cannot handle by himself. It’s impossible to do this alone. We need to get people with different knowledge to collaborate. But we can’t do that if we are not able to accept that we have limitations in our role and our own personal knowledge, so that’s a very difficult obstacle in science. And funding of course. I don’t know if it is because science is not as interesting as it was or if it’s because now we are more like an entertainment society and science doesn’t seem as entertaining as it can be to many. It may be something else.

DTM: What would be your ideal career?

MVP: I don’t know, but I know that I would love to be a scientist and a teacher in college. I did that already, and I just loved it. In college it’s different. You have a certain liberty in how you teach, and that’s great. You are not forced to finish a specific program. You can stop and really chat with the students. And instead of forcing knowledge into their heads, you can stimulate their curiosity so they can go on their own to find an answer to their questions. Teaching would be great, and I just want to do science until I’m bored with it.

I taught statistics to master’s students, and also geology and phylogeny, the classification of species, to middle school and very young students in the Muséum National d'Histoire Naturelle de Paris where I did my PhD. It was a funny way to teach to the young ones. We were looking at rocks and plants, doing a few basic experiments to learn about their characteristics, and then we would go wander in the Jardin des plantes to look at how and why the rocks are used to build buildings and how plants grow and reproduce. They could see the science inside and its applications afterwards outside.

DTM: Going on this theme of education, tell me how you would describe an exemplary scientist.

MVP: Something really important to me is humility. That’s because you have a long time of learning behind you but you have to remember that it hasn’t always been easy. This may be just me. Maybe other people at Carnegie learned everything very easily and I’m the only one who struggled. That’s possible. But teaching gives you this sense of humility because it reminds you that at one point you struggle too. So you have to remember how it was for you and how you finally understood what you are trying to teach them, find another way to explain so it can be clear to your student. It gives you a certain humility and teaches you to not be judgmental and try to help by coming down to others rather than being depreciative of their struggle. In the end, you also learn way more by listening than by turning  others down. I think humility will always help you to be better, and better in science.

Some scientists are like this. I got lucky because my PhD advisor, Matthieu Gounelle, and Larry are like this. They never turned me down when I was saying something stupid and this really pushed me to try to do better and learn more. Being respected when you are learning is the biggest help and motivation you can get to me.

 

DTM Postdoc Spotlights, conversations in which we feature our postdocs in astronomy, geochemistry, cosmochemistry, and geophysics, are edited for clarity and length.



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