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Episode 41: Planetary Science Pioneer Dr. Robin Canup

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This Women’s History Month, we are highlighting the revolutionary work of SwRI’s space science pioneer, Dr. Robin Canup. Canup is known for her trailblazing research of the Earth-Moon system. Her computer simulations and models based on the giant impact hypothesis have become the widely accepted theory on how our Moon formed. In addition to her standout scientific work, Canup is a trained and accomplished ballerina. On this episode, she takes us back to the moment when she reached her breakthrough theory on the Moon’s formation and she shares her insight on the parallels between ballet and space science. She also has valuable advice for young women searching for a career path.

Listen now as SwRI Astrophysicist Dr. Robin Canup discusses her historic findings on the Moon’s formation, her journey into space science and her experience as prima ballerina for the Boulder Ballet. 

Visit Planetary Science to learn more.


Below is a transcript of the episode, modified for clarity.

Lisa Peña (LP): March is Women's History Month. We are talking to one of our own space science pioneers making history at SwRI. Dr. Robin Canup's breakthrough research has helped us understand the formation of the planets and their satellites. We're talking to her about her historic findings and her discoveries shaping the future next on this episode of Technology Today.


We live with technology, science, engineering and the results of innovative research every day. Now, let's understand it better. You're listening to the Technology Today podcast, presented by Southwest Research Institute. Transcripts and photos for this episode and all episodes are available at

Hello, and welcome to Technology Today. I'm Lisa Peña. March is Women's History Month. A celebration of the vital role of women in American history in all disciplines and fields. As we close out the month, we're highlighting one of our own space scientists making history at SwRI. Dr. Robin Canup, an astrophysicist, and Assistant Vice President of SwRI's Space Science and Engineering division, will go down in the history books for her contributions to our understanding of the formation of the solar system. Today we're talking to her about her research, her journey into space science, and her years as a ballerina. Robin joins us from Boulder, Colorado. Thanks for being here, Robin.

Watch a simulation of Canup’s theory on the impact that formed Earth’s Moon.

Dr. Robin Canup (RC): My pleasure, Lisa. Thank you.

LP: So our listeners might be surprised to hear you were indeed a ballerina. An accomplished ballerina, I should add. We want to learn more about that in a bit. But let's start with what you are most well known for. Your research based on the giant-impact hypothesis and developing computer models that show how planets and their satellites formed. Now specifically, your computer simulations demonstrate how a Mars sized object impacted Earth creating our Moon. And your Earth-Moon formation model has become the widely accepted theory in technical literature. Will you describe this theory for us?

RC: Yes, the giant-impact theory was first proposed after we got the samples back from the Apollo mission. The samples from the Moon and the idea is that at the end of the Earth's assembly, about four and a half billion years ago, the Earth experienced a collision with another planet size object. And that collision ejected material into orbit around the Earth, forming essentially a disk of hot molten material and vaporized rock in orbit around the Earth.

And it was from that disk that the Moon then formed. So why do we think the Moon formed this way? Well, it's because of several basic clues from the current Earth-Moon system. One clue is that when we look at the density, the mass per volume of the Moon, we know, from that the Moon is lacking in iron. Which is a very dense element. Specifically, the Moon has only a very small iron core compared to other objects in the inner solar system. So we know some process that formed it must have preferentially selected for the outer layers of rocky material that don't have as much iron.
Portrait of Dr. Robin Canup

This Women’s History Month, we highlight the groundbreaking achievements of SwRI Astrophysicist Dr. Robin Canup. Her research, based on the giant impact hypothesis, shows how a Mars-sized object could have impacted our planet, forming the Moon and yielding an appropriate composition and mass for the Earth and its satellite. Canup’s computer models have shaped our understanding of the solar system.

Secondly, we know the length of our day currently is 24 hours with the Moon at its current distance, and we know the Moon's orbit is actually expanding with time. Due to the interaction with the tides, it raises on the Earth, primarily in the Earth's ocean. So we know the Moon's orbit is expanding with time. And so we know four and a half billion years ago, when the Moon formed, it was much closer to the Earth. And in the same way that as a spinning ice skater, when they pull in their arms, conservation of angular momentum makes their spin increase. We know that the same conservation would have applied to the early Earth-Moon. So when the Moon formed very close to the Earth, the Earth would have been spinning very rapidly with only about a four hour day, so that's a very rapid spin. So the giant-impact theory, if you imagine a planet-sized object hitting the Earth at an off center angle, that can naturally explain what spun up the early Earth to such a fast rotation rate. And if you imagine that the object that hit the Earth itself had an outer rocky mantle and an inner iron core and that the material that went into orbit around the Earth primarily came from the outer layers of that planetary object. The disk of debris from which the Moon later formed would then be lacking in iron. Thus explaining the Moon's lack of an iron core.

So a giant-impact theory has been preferred for some time. My particular role in it was to identify the particular type of collision. By that, I mean the size of the impacting planet, the impacting angle, the impact speed that gives you both an appropriate amount of material and orbit around the Earth to later produce our Moon. And our Moon is interesting because it's a very large moon relative to the Earth. And that leaves the Earth with the appropriate initial spin. So that four and a half billion years later, today, it's consistent with our current 24-hour day. And so that's the overview of the giant-impact theory in terms of our planet, our understanding of planet formation in general. Our simulations of the Earth and Venus and Mars, and Mercury's assembly shows that these types of large impacts would have been common during the final stages of building the inner planets in our solar system. And so, we think we have an overall picture that fits together well.

LP: So that was the problem with prior theories, is that it didn't fit together so well. There were some holes, so your information, your research, fills in those blanks. Is that how, am I understanding that correctly?

RC: Absolutely. So when I first started working on this problem in the late 1990s, it was understood that these giant impacts could produce moons. But the type of impact that could produce a moon with our Moon's mass and iron content, together with the Earth's spin, had not yet been identified. And so it was in a 2001 paper that I identified that type of collision with, as you mentioned before, numerical simulations of what happens when two planets collide.

Which is obviously not something you can simulate in a laboratory setting. We have to build models on our computer to simulate it simulate this type of event for us. And so, what's called now the canonical Moon forming impact explains the length of the Earth's day and the Moon's ball composition very well. But I should mention there are still outstanding issues that we are continuing to grapple with.

In particular, because we have rocks from the Moon, and we have, of course, we have rocks from the Earth as well. We can compare their compositions in great detail. And in particular, the lunar rocks and the upper rocks from the Earth are extremely similar in terms of their composition. Other than the issue of the moon not having an iron core. If you just look at the upper rocks from the Moon and compare them with the upper rocks from the Earth, they look almost identical. So identical, in fact, that it almost looks like the Moon came from material from the Earth itself. And yet, in general, the giant impact models tend to produce the Moon from material that came from the planet that hit the Earth predominantly, rather than from the Earth.

So that's a big current issue in moon formation theories right now, and there are several different theories that we're working on to try to explain that. So while we think we have the right general context for how our Earth-Moon System formed, there are still outstanding questions to be answered.

LP: All right, so this is ongoing research. How did you arrive at this theory, and when did you had hit on something new?

RC: It was a particular day, and I was in my office at the Institute. And I was working with data of moon forming impact simulations that had been performed by Al Cameron, who was a very senior person in the field that I worked with. And I had developed a relationship on how the mass ejected from one of these giant impacts, how it related to the spin of the planet and the mass of the disk. And I was preparing for a seminar at another university, and using that relation. I calculated that this Mars-sized impactor at a certain angle, at about 45 degrees, seemed like it would be the optimal impact to give us everything we were looking for at the same time. And so I did a simulation, and the first one was successful. And I was absolutely stunned, and then I did a series of about 50 such simulations, and within, I would say a month, we had the paper submitted. So it was an extremely exciting day.

LP: Yeah, that is exciting. Your years of research come down to this one pivotal day, and you arrive at this theory that now so many people look to for information. And as we said, it's become the widely accepted theory in technical literature. So I'm sure space scientists and researchers everywhere comb through so many ideas over their careers, and they never quite pan out. So how does it feel to have your research resonate now with so many fellow scientists and the fact that it's become so widely accepted?

RC: Well, of course, that's the dream if you do what I do. Right, you hope that you develop hypotheses and ultimately theories that stand the test of time and that ultimately prove to be correct. But for everyone that works really well, all of us have many, many, many great ideas that didn't pan out. Often in folders in a drawer at our desk, some published. So that's part of the process.

Part of coming up with new hypotheses is to realize that most of them will probably prove to be wrong. And that's something you have to be comfortable with as a scientist, and you have to be more concerned with ultimately, hopefully, getting to the truth rather than being right. But it's a great honor when you find that one of your ideas does hold up over time and seems to advance the field for at least years to a decade. That's considered a big advance.

LP: So, going back to your pivotal day in the lab with those simulations, do you remember the date? A lot of times, big moments in our lives we remember the exact date. Is it one of those for you?

RC: I don't remember the exact date. I know it was in mid-January. And I remember going into the office of my mentor and closest colleague, Institute scientist William Ward and saying, you're not going to believe what I just found. I did this calculation, and it seems like this collision should explain everything.

And I just did a simulation, and it appears to work, and his first reaction was, surely this can't be right. Surely someone else has seen this before. You better go and do some more simulations. So that's what I remember.

LP: Yeah, great. So yeah, I can imagine you're not going to believe what I have found, and it has panned out to be a great discovery at this point. So for the past, I wanted to move on to another part of your work. For the past two years, you have co-chaired the Decadal Survey in planetary science and astrobiology. Will you tell us more about this initiative and your role?

RC: Absolutely. So every 10 years NASA, for each of its science divisions, conducts or sponsors the National Academies of Sciences to conduct what we call a Decadal survey. And what this is, it is a community led effort organized by the National Academies of Sciences, which is independent from the government itself.

And that committee comes together, and typically, over the course of one to two years, that committee identifies the most important scientific questions. For, in this case, NASA's planetary science and astrobiology and the National Science Foundation's planetary science efforts as well. We identify the most important research questions for the upcoming 10 years.

And we also make recommendations for specific projects and space missions that would optimally advance science over the next 10 years. It's essentially the way for the community to tell NASA and NSF, here is what you should do to optimize the advancement of planetary science and astrobiology in the next 10 years. And it provides the scientific prioritization for those government led activities by NASA and NSF.

LP: I mean, what a huge responsibility. You're obviously the right person for the job. How do you determine what NASA should be looking at over the next decade? Oh, and also, thank you for correcting my pronunciation. It's Decadal. Decadal.

RC: It's Decadal.

LP: Decadal.

RC: Decadal.

LP: Decadal, so a lot of times, I'm learning right along with our listeners here. So Decadal. So with this Decadal survey, like I said, huge responsibility. How do you determine what stands out the most for NASA to look at?

RC: We started by putting together the Decadal committee itself. This is a group of approximately 100 people that cover all of the areas in planetary science and astrobiology and, different technical approaches, different backgrounds. So we first constitute an extremely diverse and broadly representative Decadal committee of about 100 people.

In our case, we then divided that group up into a leadership steering group of about 20 people and then six panels that were focused on topics, like the giant planet systems or Venus or Mars or small bodies in the solar system. And then, each of these panels had approximately 20 members as well.

So through meetings of each of these panels, first you identify scientific priorities, and then you consider different approaches for answering the most important open science questions. Are those theoretical models? Are those telescopic observations? Or are those related to new measurements that we need to have taken by spacecraft or perhaps by sample return?

LP: Yeah.

RC: So you evaluate. First, you evaluate what, first, you decide on what the most important scientific questions are. Then you evaluate how best to answer those scientific questions. And if you are considering potential space missions. It's part of the process that you also have those missions studied by an independent agency to evaluate their technical readiness and their approximate budgetary cost.

So that you can fit them into a realistic budgetary profile for NASA in the next decade. And then ultimately, when you have which always occurs, more great activities than can likely be supported, the final step is then to prioritize among those. To end up with a recommended portfolio of activities for the next 10 years.

LP: All right, and when does the big list come out?

RC: The big list comes out within the next three to four weeks, actually.

LP: Wow, OK. So we're close.

RC: Yes.

LP: So not quite ready to share information with our listeners yet, but something to look out for.

RC: Correct.

LP: All right. So you're a big player right now in the space scientist. Your career spans 25 plus years. Where did your scientific journey begin? How did you become interested in space science?

RC: My dad was a physicist, and so I grew up in a very scientifically oriented household. There was often a soldering iron on our kitchen table when I was growing up. I always like to point out, and I didn't think that was strange at the time. And I have to say that I always had a love of astronomy and the solar system, even in elementary school.

But it was really when I was in middle school that there was a combination of events that really captured my attention. One were the Voyager 1 and Voyager 2 flybys of Jupiter and Saturn. And the images that we saw for the first time of both the planets themselves and in the case of Saturn, the ring system and the moons of Jupiter were just awe inspiring to me.

And at the same time that was coming out, I was also watching the original Cosmos series on TV, and I was extremely inspired by Carl Sagan and his presentations in that series. And I didn't know at the time that I would end up working in this field as a career, but I had-- those were the events that really started my love of solar system science.

LP: So the seed was really planted there when you were a child, and it's just really blossomed.

RC: Absolutely. And it's been such a privilege to be able to ultimately work for my career in something that I love so much, even as a child.

LP: What are you currently working on? What is your research focus at the moment?

RC: So I have several projects in addition to my work on the origin of the Moon, which is still ongoing. I'm also working on the origin of the systems of moons that we see around the outer giant planets in our solar system. And in particular, I'm working on models for the origin of the moons of Uranus.

And this is a very interesting system because Uranus currently is essentially lying on its side in its orbit. And by that, I mean it's spinning with its North pole in the plane of its orbit. In other words, the North-- its North Pole at times points towards the sun instead of roughly at a right angle to the plane of its orbit, like our Earth is. Our Earth has a tilt of about 23 and a half degrees.

Uranus has a tilt of more than 90 degrees. So it's essentially rotating on its side, and yet it has this satellite system that is also on its side. Where all of the moons are orbiting in the plane of Uranus' equator. So it's as if you had a normal planet that was upright with a system of moons. Four big moons in particular and one medium moon, and then you just rotated the whole system by about 90 degrees and rolled it on its side.

So it's an interesting system to try to explain. So that's one of my main projects today, and then another project is looking at the origin of some of the very compact planetary systems around other stars that have been discovered. Where you see systems of planets around other stars that are orbiting well within the orbital distance where we see our innermost planet. Which is mercury.

So around other stars, we see multiple planets at very close distances around their star that look very different from our own solar system. And so, we're also working to develop models of how those systems may have formed around other stars.

LP: So, I want to move on to the reason we're highlighting you for this particular podcast. March is Women's History Month. Who comes to mind as a woman or women who have inspired your work?

RC: There have been several amazing women in planetary science that I have looked up to. Most notably is Professor Maria Zuber at MIT. I met her when I was a young scientist in the late 1990s, and she was a professor at MIT at the time. And she was also principal investigator of the GRAIL mission.

The mission that orbited the Moon, and did extremely high accuracy measurements of the Moon's gravitational field and inferred that the Moon's internal structure. From that, I've also greatly admired the current head of the planetary science division at NASA headquarters Dr. Lori Glaze. Who is a both phenomenal scientist and an extraordinary leader for NASA's planetary science.

So I was in my generation, I was very fortunate to have these amazing women role models. And increasingly now, we are seeing women take on leadership roles across our field, and these are really the highest leadership levels in our field now. And in addition to that, when we look at the incoming graduate students and people that are just entering the field of planetary science and astrobiology.

They are increasingly diverse and increasingly female rich. In terms of the numbers of young people and so that's been absolutely wonderful to see and a very inspiring evolution in the demographics of our field. And I think that many other physical sciences are seeing a similar positive shift in the diversity of people that are undertaking the scientific path career paths now.

LP: So Maria Zuber and Lori Glaze, and now young women today can add Robin Canup to the list. So it's wonderful that there are, as you said, so many women to look up to in the Planetary Sciences. Now I wanted to-- we talked a little bit about this at the top. But I wanted to go into it a little bit more now.

So while you have an extensive background in science. What our listeners might not expect is that you are an accomplished ballerina. You were Prima ballerina for the Boulder Ballet. Would you tell us about your time as a dancer?

RC: Yes. So I started dancing at age six, and I took to it immediately. And I had extremely supportive parents who brought me to dance and, ultimately, ballet lessons throughout my whole childhood. I grew up about an hour and a half north of Manhattan in New York.

And would often study not only locally in my hometown of Poughkeepsie but also in New York City. I really wanted to be a ballet dancer professionally when I was a young teenager. Ultimately when I was in my late teens, I decided that I wanted to go to college instead. So I went to college, and for a few years, I didn't do ballet. But then, when I came to Boulder, Colorado, which is where I did my Ph.D. Work, and I came to graduate school.

I started dancing again, and that's when I joined the Boulder Ballet, and for the next 10 years or so, I danced with them, and I was the lead dancer. Boulder Ballet, at the time, was a semi-professional company. So we would do two large performances in the local theater with the Boulder Philharmonic orchestra per year.

Nutcracker in the holiday season, of course, and then the spring, another full length classical ballet, like Giselle or Firebird or Coppelia or Romeo and Juliet. And so that was at the time, for about 10 years in Boulder, I really had a dual life. Both I was dancing and doing my first my graduate studies, and then my initial postdoctoral work at Southwest Research.

LP: Ballet and planetary science. How do these two interests coexist? And do you see parallels between the two?

RC: Absolutely do. They sound like they're completely different things, and yet they're both very structured pursuits. In ballet, of course, you have the classical technique and science the analogy I would say to the classical technique are the laws of physics and the mathematics. So both of them are very structured and very technical.

And they require you to be willing to work in a structured way to whatever extent you can to master those underlying techniques. In both cases doing or mastering the technique enough is not actually sufficient to making a creative contribution. In both cases, you have to work to master the technique, but you also have to transcend that in a way.

You have to use that technique to do something or answer a question or approach something in a way that's different than has been done before. And so on top of this relatively rigid technique, you have to be able to creatively push the boundaries and express yourself. And to me, it's this combination of the rigorous structure with the creative it's often referred to as artistry in the ballet world.

But I think that word really applies to creative scientific work as well. With that overlying element of creative thinking artistry and those two things working in concert, that to me was the common element that I experience in doing both of these things.

LP: Yeah, so I love that it's not just about the technique. It's about really mastering it. Pushing yourself creatively and in both cases, you're thinking outside the box and you're going above and beyond. So that's just really amazing to have done both at the same time and just the parallels between the two. Yeah, so as you explain that it's really obvious. So do you feel like your work as a ballerina were there times that that pushed you further in your space science endeavors?

RC: Absolutely. In fact, I would say that a lot of my training in ballet, both as a child and then as in my 20s, it really taught me both how to learn. How to constantly work to improve yourself and how to not give up.

How to persist even when things seem like they're perhaps too challenging for you. And so, for me, I would say a lot of my internal approaches to learning and improving came from ballet, and I still use those in my scientific work.

LP: With our theme, this month of Women's History Month, do you have advice for girls or young women interested in space science?

RC: First of all, I would absolutely encourage them to pursue the things that are of interest to them. Even if it might not be clear to you as a child or as a young adult how exactly you'll make a career out of something. If you are very interested in something and if you devote yourself to doing that well, it's amazing how successful you can be.

In a way that you won't necessarily be able to anticipate when you're young, or at least I could not have. So first, I would encourage them to pursue things of interest. To work very hard and to not be afraid of taking courses and trying things that are really difficult. In fact, the older I've gotten, the more I view doing really challenging things as the best things for us.

We know that when it comes to working out physically. We know that lifting more weights makes you stronger. But at the same thing is true mentally. The more you challenge yourself, the more you do things that are really difficult. The better and more capable you will become.

And I think sometimes, perhaps even particularly, for girls, we are reticent about doing things where we think we might fail or we think we might not be the best. But actually, I think it's often the opposite. The more that we do things that are really challenging for us, surrounding ourselves with people that are better than us and that we can learn from.

That's the situation that's actually best for developing us. So I would also encourage young women, not just with an interest in space science but the interest in anything. Do not back away from pushing yourself. Do things that are hard. Do things that are difficult, and don't be afraid to fail or to not be the best one in the room at the moment. Because that's the path that will help you optimize your own potential throughout your career.

LP: Thank you for sharing that. That's wonderful. What would you like your legacy in the space science field to be?

RC: I hope that some portion of the theories and the models that I've developed for how planets and their moons form, even if they don't ultimately turn out to be correct. I hope some of them will be obviously, but even if they don't ultimately turn out to be correct. I hope that they've played a substantial part in advancing thinking.

Because in science, because so many of our theories turn out not to be correct, it's not only the few theories that turn out to be very long lived and that we think are correct that matter. It's also the theories that advance thinking in general. So I hope that my work on, in particular, planets and the origin of their rings and moons has a positive impact on thinking when people look back on it.

And then, I hope that the Decadal survey that I was co-chair of this past two years I hope that will be a lasting legacy for the next decade. And that it will help support and direct an extremely, another extremely successful decade of planetary exploration going forward.

LP: All right. I'm looking forward to learning about what that survey uncovers, and it's going to be wonderful following what you do next. So, Robin, you were certainly an inspiration. It was wonderful learning about your background, your path to space science, and how you're shaping the future as you continue your groundbreaking research in making history in your field.

I mean, really, what a great role model and a prime example of why we celebrate Women's History Month. Thank you so much for joining us today.

RC: Thank you, Lisa. And best wishes to everyone out there.

And thank you to our listeners for learning along with us today. You can hear all of our Technology Today episodes and see photos and complete transcripts at Remember to share our podcast and subscribe on your favorite podcast platform.

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Ian McKinney and Bryan Ortiz are the podcast audio engineers and editors. I am producer and host, Lisa Peña.

Thanks for listening.


Our planetary science program focuses on solar system bodies and their atmospheres. Using observational data from space- and ground-based instruments and numerical and theoretical analysis, we investigate the origin, evolution, and current state of solar system objects including Mars and Venus, Earth’s Moon, asteroids, comets, Jovian Trojans, the satellites of the outer planets, and Pluto and other Trans-Neptunian Objects.