Postdoc Spotlight: Asmaa Boujibar explores planetary cores to distant stars
Asmaa Boujibar joined Carnegie Science in 2016 after working for NASA as a postdoc. She was the first Moroccan woman to work for NASA, a claim to fame that has allowed her to be a role model for young girls around the world.
She explored many scientific collaborations on the Carnegie campus, which allowed her to look beyond experimental petrology into cosmochemistry, astronomy, geophysics, and machine learning. The broad scope of her research spans from the composition of planetary cores to the evolution of stars. During quarantine, Boujibar has been working to compile a massive database of core differentiation experiments that date back to the 90s.
She also recently became a mother to a beautiful baby girl! Congratulations!
As Boujibar plans the next phase of her life as an Assistant Professor at Western Washington University, we sat down with her for a postdoc spotlight.
(Interview has been edited for length and clarity)
First, please introduce yourself! Who are you and what is your area of research?
Hi, I’m Asmaa, currently a postdoctoral fellow at the Carnegie Science Earth and Planets Laboratory. I am an experimental petrologist focusing on planetary formation and differentiation.
What do you study and why is that research important? What are the broader implications?
My research uses experiments conducted at high pressure and temperature to simulate conditions under which planets form and evolve. I use experimental data to model the chemical reactions occurring during planetary growth and the resulting physical and chemical states of planetary interiors. I also apply machine-learning algorithms to meteoritic data, which hold keys to the early stages of our Solar System.
My work is essential to understand how and why each terrestrial planet of our Solar System and beyond are different in chemical composition, structure, thermal state, and geologic history. These questions are important to figure out how a planet forming in specific conditions or exhibiting specific features can be habitable.
What did you work on at Carnegie when you first got here?
I started my postdoc working on core formation, looking specifically at how alkali metals—sodium, potassium, rubidium, and cesium—distribute between metal and silicate phases. The goal of my work was to assess whether any of these elements are present in the cores of planets.
Usually, elements like sodium and potassium end up in the crust whenever you have magmatic differentiation as a planet forms. So, the crust is saltier than the core! However, previous experiments showed that when you have sulfur going into the core, you can get a bit more potassium there as well. When I started, we didn't have much information on any of the other alkali elements like sodium. So, I ran experiments in the lab to see how much of these elements could be trapped in the cores of Earth, Mars, and the asteroid Vesta.
My data suggest that significant amounts of these elements could have been trapped in the cores of planetary bodies formed enriched in O and S, such as Mars and asteroid Vesta.
You recently published a paper with other Carnegie staff scientists Yingwei Fei and Peter Driscoll that steps outside of our own Solar System to look at super-Earths and explores the density and melting properties of MgSiO3. What is MgSiO3 and how did you study it?
MgSiO3 is a fundamental material in planetary science, representing most of rocky planets interior (80% of Earth’s mantle). Understanding how this material behaves at the high pressures of planetary interiors is crucial to predict how a planet evolves and can eventually become habitable. Most discovered rocky exoplanets are larger than Earth, called super-Earths, with very high internal pressures and temperatures. This study provides invaluable data on MgSiO3’s properties at the highest pressure range ever explored, obtained at the Sandia National Laboratories’ Z Pulsed Power Facility.
These experiments were made possible by the unique capabilities of the Z machine to generate ultra-high pressures by shock compression and the chosen starting material. It is usually difficult to reach these pressures in this kind of experiments with MgSiO3 glass or low-pressure crystals (enstatite). The trick was to first compress this material with a multi-anvil press at the Earth and Planets Laboratory, to produce large crystals of bridgmanite (high-pressure form of MgSiO3), and then take them to Sandia National Lab to compress them at even higher pressures.
What does this work tell us about exoplanets and habitability?
This study showed that MgSiO3 has a very high melting point. I modeled the internal structure of super-Earths to calculate how pressure, temperature and density increase within these planets. Last year I ran the same models with literature data—this time it was really exciting work with the most accurate and high precision data on such difficult experiments.
One of the most important questions to address for exoplanets is whether the core is solid or liquid. When you have a core that is partially solid like Earth, you can more easily have convection. The movement of the liquid creates this magnetic field, which protects us from cosmic rays and is essential for understanding habitability.
The paper showed that super-Earths are very likely to have a partially solid core in the course of solidification. That's very exciting because it means that super-Earths may likely have magnetic field protection!
You also recently published a paper that uses cluster analysis to analyze “presolar grains.” What is a presolar grain?
Presolar grains—often called stardust—are tiny minerals formed before the birth of our Solar System, in outflowing and cooling gases of earlier stars. These grains are unique as they bear information of astronomical reach: they could form as early as ~7 billion years ago, could have traveled across the whole galaxy, or even possibly resulted from transfer from other galaxies merging with ours.
You don’t have to be a scientist to comprehend the remarkable value of such materials when picturing the outstanding range of distances and time these grains can sample. As a result, by analyzing presolar grains in the lab, collected data provide invaluable information on the chemical evolution of the Galaxy, stellar evolution, nucleosynthesis, and interstellar processes these grains experience throughout their long journey to our Solar System.
Can you briefly summarize what you found in this study related to presolar grains, “Cluster analysis of presolar silicon carbide grains: evaluation of their classification and astrophysical”?
Presolar grains have isotopic compositions that are remarkably different from materials formed in our Solar System. This specific chemical signature makes them easily recognizable when analyzing them with appropriate instruments such as a nano-SIMS. Their isotopic compositions are also used to classify them and infer the environments of their formation, for example in evolving red giant stars or exploding supernovae. Our study is the first one using a machine-learning algorithm (cluster analysis) to evaluate the traditional classification of presolar silicon carbide grains. It provides a more robust statistical approach to group these grains and better understand their formation.
Using this method, we found a group of grains having the same range of isotopic compositions, which may be the average composition of evolving red giant stars in our solar neighborhood. Alternatively, these grains may have formed following a galaxy merger that led to an enhanced stellar formation. In addition, we found that several aspects of the former classification of SiC presolar grains rely on arbitrary definitions, due to the limitation of our visual separation of objects. For instance, the type of grains Y and subtypes AB1 and AB2 were previously defined based on the solar value of a single isotopic ratio. Our analysis proposes a better method to define these grains based on a multi-dimensional approach. The new divisions we found happen to be in better agreement with astrophysical models.
How did you go from studying the inside of planets to stardust?
I started working with Yingwei Fei and Peter Driscoll after my original work on alkali partitioning in the core. We used intensive computer modeling to look at the interiors of the super-Earths. They only had six months to finish up the project, so I had to learn how to code really fast!
After that project, I had built up my coding skills and I knew a bit about meteorites. I proposed other Staff Scientists, Robert Hazen, and Shaunna Morrison if they are interested to collaborate on a project applying machine learning to meteorite components. After several discussions with other staff scientists on campus, like Larry Nittler, the project on stardust classification was born. I was able to switch gears to work with Robert Hazen, Larry Nittler, and Shaunna Morrison on the classification of stardust using cluster analysis and machine learning.
What have you been doing since COVID hit?
Now, I’m coming full circle back to planetary core differentiation! During this COVID, because of all this time being at home, I built a database of almost all experiments about metal and silicate phases that try to replicate core formation that have been published since the 90s. We are now applying machine learning algorithms again—just like the stardust project— to see if there are any other trends that we haven't caught so far. Plus, we want to see if there are any spots where we need to do more work to fill in the gaps.
What’s the coolest thing you’ve worked on at Carnegie Science?
There are two sides to my research projects that I found very exciting. First, discovering new fields and expanding my knowledge in planetary science at various scales was very enriching. I was originally working on planets in our Solar System and then exoplanets close to us that we can look at with telescopes. Then I moved onto these tiny bits of stardust we find in our Solar System that came from former stars formed before our Solar System, which could have even recorded chemical signatures of other galaxies! It has been fascinating to take on new fields of research spanning such a huge array of time and space. The other cool aspect of my work at Carnegie was the originality of the techniques I used. It was very exciting to be the first to use machine learning and visualization algorithms to tackle various questions such as the classification of meteorite components and chemical reactions occurring between planetary cores and mantles.
What inspired you to work across these scales and different projects?
It was really the culture here at Carnegie. I think the Carnegie Earth and Planets Laboratory is a very special place with an ideal number of people and interesting overlaps between research areas. There is also a culture of having lunch together, having beer hour, seminars, reading groups, and all of these social activities that enable collaboration. The fact that I grew up speaking three languages and in multiple cultures might also have influenced me in taking a multi-disciplinary approach.
Some people may not know this, but you’ve been knighted by the King of Morocco for being the first Moroccan woman to join NASA before you came to Carnegie. How does it feel to be a knight?
You know, there are not a lot of physical scientists from North Africa and the Middle East—that’s even more true for women scientists. There are few role models for people like us. To me, the most important thing to come from this decoration from the King of Morocco is that it has inspired many young girls to see science as a possible future for themselves.
I feel similarly about the #DreamBigPrincess campaign that I worked on with Disney and the United Nations. At first, I didn’t really want to do all these interviews and talk about my work at such an early stage of my career. But once I started getting messages from young girls and Moroccan students who were inspired by my accomplishments, I realized how important this kind of outreach can be for people who aren’t normally represented in the sciences.
On a lighter note, what do you do in your free time?
I play guitar, sing, and play the drums. I actually just had my first gig this past Saturday. My partner Will is a professional musician and I played in a bar with him. There are actually a lot of scientists at Carnegie who are musicians. Larry Nittler plays the keyboard with a jazz band, Bob Hazen used to play trumpet in an orchestra and Andrew Steelie plays guitar in a rock band. It’s cool to see that you can be a scientist and a musician at the same time.
Do you have any advice for current grad students?
First, it’s really important to have a good work-life balance, to reduce stress and fatigue, prevent burnout and stay productive. Grad school can be very stressful and take all your attention. Hobbies would help you shift your focus to do something enjoyable outside your work and return refreshed and recharged to take on new challenges. Having other activities also helps you broaden your skills in general, which can provide new perspectives and give you more confidence to overcome new challenges.
And if you have a chance to broaden your skills at the workplace, take it! Talk with other scientists. Be curious about their work. You never know if your work could benefit from a collaboration or you could learn a new skill. When you’re doing your Ph.D., you’re not just learning your specific area of research. You’re learning HOW to learn. You’ll be surprised how fast you can pick up a new topic. You’ll learn faster than before you were a Ph.D.
What’s next for you? What are you looking forward to?
Next, I’m moving to Washington to be an assistant professor at Western Washington University. I will be working jointly in the Department of Geology and the Department of Physics and Astronomy. This new position closes another loop. I can use my diverse set of knowledge in planetary science and share my passion with students in geology, physics, and astronomy.