Planetary Radio • Oct 25, 2023

Simulating Psyche: Modeling craters on a metallic world

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Simone Marchi

Senior Research Scientist for Southwest Research Institute

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Kate Howells

Public Education Specialist for The Planetary Society

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Bruce Betts

Chief Scientist / LightSail Program Manager for The Planetary Society

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Sarah Al-Ahmed

Planetary Radio Host and Producer for The Planetary Society

NASA's Psyche mission launched on Oct. 13, 2023 on a journey to explore its namesake, the metallic asteroid Psyche. Simone Marchi, co-investigator for the Psyche mission, joins Planetary Radio to share the creative ways their mission team is working to understand cratering on metallic worlds, including everything from computer modeling to blasting metallic meteorites with projectiles. The Planetary Society's Public Education Specialist Kate Howells will discuss the Japanese Space Agency's newest moon mission, SLIM. Then, Bruce Betts, the chief scientist of The Planetary Society, will share his experiences with crater modeling and a fresh random space fact.

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Psyche launches
Psyche launches A SpaceX Falcon Heavy rocket carrying NASA's Psyche spacecraft lifts off on Oct. 13, 2023.Image: SpaceX
Psyche the spacecraft at Psyche the asteroid
Psyche the spacecraft at Psyche the asteroid This artist's illustration depicts NASA’s Psyche spacecraft exploring the asteroid Psyche.Image: Credits: NASA / JPL-Caltech / ASU / SSL / Peter Rubin
Psyche the asteroid
Psyche the asteroid An artist’s concept.Image: NASA/JPL-Caltech/ASU
SLIM rolling out to the launch pad
SLIM rolling out to the launch pad The H-IIA Launch Vehicle rolls out to the launch pad with the XRISM and SLIM spacecraft aboard.Image: JAXA


Sarah Al-Ahmed: You think asteroid Psyche is totally metal, wait until you hear how the mission team models its craters, this week on Planetary Radio. I'm Sarah Al-Ahmed of The Planetary Society, with more of the human adventure across our Solar System and beyond. NASA's Psyche mission to explore a metallic asteroid has finally launched and it's headed to its asteroid namesake. Simone Marchi, co-investigator for the Psyche mission joins us this week to share the creative ways that their team are learning more about cratering on metallic asteroids. And by creative, I mean their straight-up blasting things at meteorites. It's amazing. Kate Howells, The Planetary Society's public education specialist and Canadian Space Advisor, will also pop in to tell us more about the Japanese Space Agency's newest moon mission, SLIM. Then our friend, Bruce Betts, the chief scientist of The Planetary Society will share his experiences with creator modeling and a fresh, new, random space fact. If you love Planetary Radio and want to stay informed about the latest space discoveries, make sure you hit that subscribe button on your favorite podcasting platform. By subscribing, you'll never miss an episode filled with new and awe-inspiring ways to know the cosmos and our place within it. There's been so much awesome space news recently that you may have missed the launch of SLIM, the Japanese aerospace exploration agencies or JAXA's newest moon mission. On September 6th, 2023, SLIM blasted into space aboard an H-IIA rocket from Tanegashima Spaceport in Japan. A huge congratulations to the team from everyone here at The Planetary Society. Kate Howells, our public education specialist and Canadian Space advisor, is here with the details. I love seeing you and everyone in the office, but it's extra special to see you. You live in Canada, so thanks for coming all the way out here.

Kate Howells: Oh, it's my pleasure. It's great to be able to be in person with everyone and be in the office, which is the coolest place in the world.

Sarah Al-Ahmed: It really is. I bet if we just recorded this week and let everyone see all of our adventures and how cool everyone is here, it would be.

Kate Howells: If you could somehow do an audio tour of the office and all of the cool space stuff that's in here, it'd be so good.

Sarah Al-Ahmed: Oh, that's an idea for a future show. But we're here to talk about the Japanese Space Agency's SLIM mission. You didn't write this article. One of our freelancers, Andrew Jones, wrote it. He's always a fantastic writer about space agencies that we frequently don't hear enough about. So what is JAXA SLIM mission?

Kate Howells: So the SLIM mission, SLIM stands for Smart Lander for Investigating the Moon, and this is an experimental mission from the Japanese Aerospace Exploration Agency, AKA JAXA, and it launched in September. It's on its way to the moon. It's going to get into a particular orbit as spacecraft do, they take these long journeys to get to just the right place. It's going to try to land on the moon in early 2024. And what's special about SLIM, well, there's a few things. The main goal of the mission is to demonstrate a very precise landing. So most of the time when something aims to land on the moon, it sets a target ellipse. So a sort of elliptical shape area that it's trying to land in. That's usually a few kilometers in length or a few miles for American or UK listeners. For the SLIM mission, it's trying to land within a target area of a hundred meters or 330 feet.

Sarah Al-Ahmed: Wow.

Kate Howells: So this is a much smaller, it's really like a precise target that they're trying to hit. So if they're able to do this, it will advance lunar landing technology. It'll also make Japan the fifth country to land on the moon. India just recently became the fourth, and so it would be an expansion in the number of countries that are able to achieve lunar landing.

Sarah Al-Ahmed: I mean, that's a really useful technology because so frequently we see these situations where it's like, okay, we have this landing ellipse, but what if there's a rock? What if we accidentally end up in a crater? And especially on the moon, I imagine trying to get out of those craters if you're a little rover is almost impossible.

Kate Howells: Yes, certainly. So being very precise is very helpful. Also, one of the reasons they want to develop this precision is that as we advance lunar exploration, settlements on the moon, that kind of thing, you're going to need to make sure that you can be very precise in your landing. If we have lunar settlements built, you don't want to accidentally land on one of them if you're trying to land nearby. So the other thing too that they point out is that as lunar science advances, we're going to want to be precise in where we land scientific spacecraft because if you want to investigate something in particular and you don't have rover technology, you just have a lander, you want to make sure you land it in the area of scientific interest. So this technology, if it works, could advance exploration and science.

Sarah Al-Ahmed: Super cool. And I understand too that there are some really weird rovers and things that this mission is going to be deploying.

Kate Howells: Yes. So SLIM carries with it two small rovers that are very unconventional in the way that they go about roving. One of them called Lunar Excursion Vehicle 1, very creative name uses a hopping mechanism to get around, and the other one, Lunar Excursion Vehicle 2 uses a sort of rolling mechanism. It's about the size and shape of a baseball, so it's a spherical rover and it moves around by separating its two halves and sort of crawling in a rolling manner by swinging from side to side to propel itself forward. So it's just a very cool new way of moving about on another planetary body, and I really hope it works and we get to even see it, some kind of animation of how it might look, but these rovers also carry cameras on them, so we might even get to see some firsthand imagery from the rovers.

Sarah Al-Ahmed: Whether or not they work, that imagery is going to be awesome.

Kate Howells: Yes, agreed.

Sarah Al-Ahmed: It just makes me so happy that so many more nations are going to the moon. It's really an international effort these days, and it feels like this Artemis Accords Coalition has really taken shape.

Kate Howells: Yeah, absolutely. The future of human space flight on the moon and also just lunar investigation is very much a global effort. We're seeing this so much more compared to during the Apollo era, and there's actually a really great infographic in the September issue of the Planetary report, our quarterly member magazine, but that's also available online for free to everybody. There's an infographic that compares the Apollo program with the Artemis program looking at things like how many countries were involved, whether commercial partners were involved, and you can see how much more international and just generally collaborative the Artemis program is.

Sarah Al-Ahmed: And I'll put a link to that on this episode of Planetary Radio along with the link to this article so that you can read more about JAXA's new ideas for how to land on the moon. Well, thanks for joining me, Kate.

Kate Howells: Thank you, Sarah.

Sarah Al-Ahmed: Speaking of recent amazing space launches, NASA's Psyche mission launched on October 13th, 2023. It went to space aboard a SpaceX Falcon Heavy Rocket from Launchpad 39A at NASA's Kennedy Space Center in Florida, USA. I've been so looking forward to this mission's launch. I could tell you all about it, but let's hear it from Lindy Elkins-Tanton, the principal investigator for the Psyche mission. Here's what she told me during our first conversation on Planetary Radio in March 2023.

Lindy Elkins-Tanton: The Psyche mission is named after the asteroid Psyche, which orbits out in the main belt between Mars and Jupiter. Now, why would we want to go to this asteroid among the ... what's the estimate between one in two million asteroids in the main belt I think so here's this one particular one. It's because it seems to have a metal surface, and we as humans, we visited bodies made of rock like the Earth and bodies made of gas and ice like Jupiter and Neptune and icy moons but we have never visited a metallic body, and there are only a few in our Solar System. We think maybe nine of the asteroids are made of metal, and this is the biggest one. So I feel like it's the space equivalent of discovering Antarctica. It's a new kind of place that humans have never been, and frankly, it is a big mystery, which is what makes it exciting to me.

Sarah Al-Ahmed: We'll be hearing from Lindy again in our next show. I can't wait to learn about her experience during launch day. Can you imagine working on a space mission for years and then finally after all of that time and effort, getting to watch it soar into the sky? It gives me chills just thinking about it. One of the reasons I'm so excited for the Psyche mission to reach its target is because I want to know what craters look like on a metallic asteroid. That has to be completely mind blowing. Our guest this week is an expert on the subject. Simone Marchi is a staff scientist at the Southwest Research Institute in Boulder, Colorado USA. He's co-investigator for Psyche, but that's just one of the many missions he's worked on. He's also deputy project investigator for the Lucy mission, which will investigate Jupiter's Trojan asteroids. Simone is deeply involved in understanding the bombardment history of our Solar System through the cratered terrains of terrestrial planets and asteroids. Let's learn more. Hi, Simone.

Simone Marchi: Hi, Sarah.

Sarah Al-Ahmed: Thanks for joining me and congratulations on the successful launch of the Psyche mission.

Simone Marchi: Oh, thank you, and my pleasure for being here.

Sarah Al-Ahmed: It's got to be really exciting working so long on something and to finally see it go up. Did you get a chance to be at the launch?

Simone Marchi: Yes, indeed. Yes. Both things you said are important. First thing, we've been working on this mission for a long time already, and it was very nice to see liftoff and go to space. And I was also able to be there in person, which was also very exciting, because any launch of a mission is always a very exciting moment, particularly so if you are involved directly with the mission that's going to fly.

Sarah Al-Ahmed: And you've been involved with so many missions, have you been able to go to other launches that were four missions you've worked on?

Simone Marchi: Yes, I've been involved and still are involved with other missions. So this was not my first launch, but it was my first Falcon Heavy Rocket, and so that was an additional element of interest for me.

Sarah Al-Ahmed: Did you get to see the boosters come back down and land?

Simone Marchi: Oh, yes. In fact, I planned my location to be as close as possible where the booster were supposed to land, and I was able to see that clearly, and it was just amazing.

Sarah Al-Ahmed: The reason I wanted to have you on this show is because we've talked about the Psyche mission before and how exciting this object is. A metallic asteroid is not something that we can study every day, but what I'm particularly curious about is our understanding of cratering on a metallic body. And you are someone who I understand has been deeply involved in trying to understand this process. So how did you fall into this? How did you end up in a situation where you were trying to figure out how craters form on a metallic asteroid?

Simone Marchi: Yeah, that's a very good question, and you have the right person here because I've been obsessed with craters and I've been studying craters for over 20 years. And I can say that I have studied craters all across the Solar System ranging from planet Mercury, Earth, Mars, Venus even, although there are not many crater on Venus, and then all the way to other asteroids. So it's really something that fascinates me and what we see in a crater is just what's left behind of a very energetic process. The physics of that, it's what interests me. And eventually we studied that by looking at the craters that we find on the surface. So when we started looking at Psyche mission and Psyche asteroids and then trying to plan this mission, it becomes obvious that if this is a metallic object as we think it might be, well then we are dealing with the situation that we don't really have seen in the past. All the objects we have visited so far are either rocky objects or icy objects. And so we have a good understanding, I would say, of what the crater look like on a rocky object. But how about metal? We don't really know. We have never seen that before. And so this was sort of exploring completely new avenue for me to think about cratering on this object. And so that was very exciting. One of the things that fascinates me about this mission.

Sarah Al-Ahmed: It's got to be one of the things that's most fascinating for me. It's a very strange object, but I'm trying to imagine in my mind what these craters might even look like. And without going there, the only thing we can really do is model or conduct experiments here on Earth.

Simone Marchi: Yes.

Sarah Al-Ahmed: When we say that this is a metallic asteroid, what kind of materials are we talking about?

Simone Marchi: Yeah, so here is the thing. This is an object that's very far away from us, and we have a very limited understanding of the actual bulk properties of these objects. And so we infer, for instance, using telescopes, big telescopes even on Earth or even space telescopes such as the Hubble space telescopes or even the James Webb. And so using those facilities, we can get the sense of what the composition might be. But the fact of the matter is that we do not really know. We have proxies perhaps. So if we look at meteorites, right, these meteorites are presumably chunks of asteroids that naturally come to us. We don't have to go to space to pick them up. They candidly come to us. And so there's a class of meteorite, which called iron meteorites that are made of iron and nickel for the most part. And so these are very dense meteorites. And so potentially those kind of alloys that we find in this meteorites may be present on Psyche or there could be other components that are added to the mixture. As a matter of fact, one thing that we know about Psyche is that the overall density of the asteroid, it's somewhat lower than the density of a solid piece of iron meteorite. And so that would imply that Psyche cannot not necessarily be an intact large chunk of iron-nickel metal like those meteorites. Will have to contain some other elements. What those elements are, it's not obvious. It may be just simply voids or that could be silicate, meaning other rocks embedded with it. So that's still to find. We'll figure it out once we get there. But the general idea is that there might be a significant amount of iron, which might be similar to what we see in this iron meteorite. So we're talking about basically iron and nickel alloys.

Sarah Al-Ahmed: For anyone who's ever had a chance to go to a science museum and hold one of these metallic meteorites, we had a chunk of it from Meteor Crater in Arizona that I picked up. And despite being maybe the size of a large grapefruit, that thing was like eight pounds. It was really heavy.

Simone Marchi: Really heavy.

Sarah Al-Ahmed: I encourage everyone to go out and try to pick one of these things up because you'll be very surprised.

Simone Marchi: Yeah. But be careful please, because the first time I actually took in my hands one of those meteorites, I didn't really appreciate how heavy they were. And so you can easily break your foot if you're not careful enough.

Sarah Al-Ahmed: It's true. When I previously worked at Griffith Observatory, there's a desk where we keep one of those, and the floor unfortunately got very dented for a while there because despite warning people, they'll still drop that thing and just right into the ground.

Simone Marchi: Yeah.

Sarah Al-Ahmed: So we're testing these other meteorites to see how they compare. Do we have any spectroscopic data that can give us an understanding of maybe what the surface material is like?

Simone Marchi: Yes. So as a part of the telescopic observations that we're talking about a moment ago, we certainly also have spectral data, and it is using spectral data that we can try to infer the surface composition. But here is the strange thing about a metallic object, that in fact, if you take a spectral observation in the visible and near infrared wavelengths, which is most easily accessible for ground-based facilities, well then you end up with something that doesn't necessarily show you a great deal of details. In other words, when you look at a spectrum, you will like to see absorption bands. If you have an absorption, that means a dip in the spectrum. Well, that tells you what kind of materials you might have. Different materials have different characteristic absorptions. And so by measuring those, you can figure out what kind of material you have. Well, the problem is that metal, this type of metals at least do not really have many absorption bands at all. And so what you're looking at, it's almost a featureless line, and therefore it's hard to pinpoint what the composition might be. And to make this story even more complicated, there are other completely different class of materials that have similarly featureless spectra. For instance, you can hold in your hand a piece of a carbonaceous chondrite meteorite, which is an assemblage of silicates. There's potentially significant amount of carbon in it, and other ... there could be metal as well. But now, if [inaudible 00:18:15] spectrum that it's also kind of featureless, and so all of a sudden we're dealing with this data that it's not conclusive in what the composition might be. And so this implies that we need to keep our minds open because we may see things differently than what we are anticipating.

Sarah Al-Ahmed: Every time we've been to an asteroid so far and gotten up close, they've constantly surprised us. For an example, when they went to Asteroid Bennu and touched the surface, that thing was so rocky and full of little tiny bits that the spacecraft almost got entirely swallowed up by the asteroid just by contacting it. So I'm sure that Psyche is going to completely surprise us.

Simone Marchi: Yes.

Sarah Al-Ahmed: So how are we actually attempting to try to model these craters? Are we using computer models primarily?

Simone Marchi: We have two means for doing that. Well, the first one will be certainly computer models. We can run sophisticated models in which we simulate a collision, and so that could give us a sense of the outcome. Now, we can set up the model to be realistic for an iron-nickel alloy and so that would give us a sense of what might happen in reality for that kind of collisions. But there is another way of approaching this, as you briefly alluded before, that is doing in fact experiments in the lab. And that has become an important endeavor, at least for me, try to understand how craters may look like on a metallic asteroids. So we have been conducting experiments used primarily the NASA Ames Vertical Gun facility, the AVGR facility in California, which has been built to conduct this kind of experiments. And so our approach was then, well, we should try to shoot some of this high velocity impactors into a target that might be similar or in a way might represent psychic compositions. And so over the course of the last few years, we have done several such experiments. And so I think we are building a little bit of a better understanding of what we might expect to see how those craters might look like on a metal rich object.

Sarah Al-Ahmed: I love that you bring that up because in a previous week, I believe I was talking with Matthew Siegler, we were talking about a completely different subject, but I asked whether or not people have been conducting these experiments where you actually shoot things into metal to see, and he was like, "You have to talk to someone who's been doing this because I hear that it's a lot of fun." So have you actually been going there in person and just conducting these experiments, having a fun day shooting things into sheets of metal?

Simone Marchi: Yes. Well, it's even better than that.

Sarah Al-Ahmed: How does it get better than that?

Simone Marchi: Yeah, it gets better than that, because we're not just using any random scrap metal or piece of metal. We are actually using iron meteorites.

Sarah Al-Ahmed: Oh, wow.

Simone Marchi: Yeah. And so a big part of this was to make this as realistic as possible. So iron meteorites comes in a wide range of properties. They have different crystal structure, crystal composition, and so there's a great variety of possibilities there. And so the question is now, how do we go about simulating this in the lab? I mean, in principle, yes, we could cast some iron and use that in a lab made samples, but we were not able to reproduce the complex texture and composition that the real meteorites have. So in fact, the first set of experiments, just to make sure that I think we were going in the right direction, we're done with lab made samples. So these were iron-nickel alloy that we cast with the foundry. We got some blocks out of it, and then we did some tests, but then we quickly realized that we really needed to go to the real thing, meaning the iron meteorites. And so then we started, try to acquire iron meteorites from various localities. And here I mentioned that the Arizona State University was important for this endeavor because they have a great collection of meteorites and they were able to give us some of their samples so that we could conduct the first sets of experiments. And so we actually did this with three different types of meteorites. And the most amazing thing is that when you start using the real meteorites, because they're complex, as I said earlier, you then see that the outcome of the event, it's very different than if you were to use say any other piece of scrap metal that you can find. And so that is why we want to do that. And so realizing that has brought up sort of going farther down the rabbit hole and try to gather more diverse type of iron meteorites and keep doing this. So we have done quite a bit at this point.

Sarah Al-Ahmed: I was going to ask how you got those meteorites, but I love that you sourced them from ASU. In my imagination, I could just see people going to Antarctica and combing the ice for enough meteorites to get the science done.

Simone Marchi: Well, that would be fine. I have not done that myself. We have also purchased meteorites from ... iron meteorites from other vendors. Not all of our meteorites come from ASU. Because as it happens, you can buy iron meteorites relatively easily and they're a bit expensive, but clearly, it's all justified because we really need to see what happened with this kind of experiments in order to be prepared. It's an important component of eventual interpreting what the spacecraft will find. As a general comment, I would like to make the cratering and information of crater is perhaps one of the most fundamental evolutionary processes that we have on asteroids, right? Once they're formed early on, there could be sorts of things happening, but then they basically freeze for billions of years, and then the only thing that can really shake them up are larger scale collisions. And so they're going to be important part of the story that will unfold as soon as we get to the asteroids, and so we better be prepared for that.

Sarah Al-Ahmed: What were the biggest differences between the actual iron meteorite tests and the ones done with just sheet metal? Did it change the shape or how did that work?

Simone Marchi: So we have done several experiments, right? So we're building up our understanding. The first batch was just any regular metal that we could find, and so we did some experiments and we produced some little craters on them. They were nice and were already exciting by doing that. Then we turned our attention to the iron meteoroids. And the first several experiments that we did, they looked pretty much the same as the previous one that we did with some scrap metal. And so first conclusion was, well, maybe it doesn't really matter that we use the meteorites. Maybe we should just keep doing ... not using the meteorites, not to waste the precious material. And because in the end, the morphology of the crater is kind of similar. Well, we kept doing a few more experiments with iron meteorites, trying to increase the energy of the collision, and all of a sudden we realized that there was something unexpected, at least to me that was happening. Well, that is the way the method crux. In fact, all the experiments that we did with regular terrestrial metal, we didn't see any major cracking forming in our target. In a way, they are very ductile material, and so they adjust, and it's not like a rock that will fall apart and completely crack in all directions, the metal behave differently. But when we started increasing the energy of some of our iron meteorite target, they start to crack in ways that we could not understand. In fact, as of today, that's still a bit of a puzzle for us, and we are planning to do more experiments in understanding how you can destroy a chunk of metal. That's very important for us because now imagine you have Psyche possibly contain lots of metal, and then all of a sudden you have a massive collision that could have taken place billions of years ago. So now the question is, what that type of collision do for this in terms of cracking and breaking the asteroids, it's perhaps something we should be considering. And so all of this is sort of a new line of investigation, if you will, that we haven't really thought when we started doing this, and it's become very, very fascinating and interesting.

Sarah Al-Ahmed: This is a guess, but is the metal shearing along crystallization lines? Is there some indication within the structure of the material that lines up with those cracks when you do these tests?

Simone Marchi: Yes and no. That's a puzzling thing.

Sarah Al-Ahmed: Yeah.

Simone Marchi: Occasionally we find a crack that seems to be aligned with the crystal boundaries. Some of these meteorites, as I said earlier, clear crystal structure. You can clearly see, these are big crystals of the most common, at least are taenite and kamacite. These are alloy of iron and nickel in different proportion and different chemical arrangement. And so you see sometimes these large crystals, and you would expect naturally as you suggested, that the crack will follow that boundary line. And sometimes they do, but not all the times. And we don't understand why at some point the crack decides completely to go off in a direction that apparently has no reason why. There's another aspect of interest here along those lines is that some of these meteorites, in addition to this crystal structure, they also have inclusions, meaning they have bits and pieces of different type of composition. This could be a chunk of graphite, so something that contains lots of carbon. It could be something that contain lots of sulfur. It depends. Every meteorite is different. And again, you will expect that because this inclusions are a discontinuity in the metrics of the meteorite. We expect they could have something to do by driving where a crack would form. And yes or no, again. Sometimes we see, yes, there is an inclusion here. It's a big crack pointing towards the inclusion, but there are other cases in which cracks go completely in another direction, and it seems don't care much about the fact that there are inclusions around. And so it's a puzzle. We're still investigating this.

Sarah Al-Ahmed: It's so cool though. Where are you keeping all of these bits of meteorite that you've shot things into? Is there an archive where you've got them all lined up somewhere?

Simone Marchi: As a matter of fact, currently they're all in my office. It's just behind my desk.

Sarah Al-Ahmed: That's amazing. We'll be right back with the rest of my interview with Simone Marchi after this short break.

Bill Nye: Greetings, Bill Nye here, CEO of The Planetary Society. Thanks to you our LightSail program is our greatest shared accomplishment. Our LightSail 2 spacecraft was in space for more than three years, from June 2019 to November 2022, and successfully used sunlight to change its orbit around Earth. Because of your support, our members demonstrated that highly maneuverable solar sailing is possible. Now, it's time for the next chapter in the LightSail's continuing mission. We need to educate the world about the possibilities of solar sailing by sharing the remarkable story of light sail with scientists, engineers, and space enthusiasts around the world. We're going to publish a commemorative book for your mission. It will be filled with all the best images captured by LightSail from space, as well as chapters describing the development of the mission, stories from the launch and its technical results to help ensure that this key technology is adopted by future missions. Along with the book, we will be doing one of the most important tasks of any project. We'll be disseminating our findings in scientific journals at conferences and other events, and we'll build a master archive of all the mission data, so every bit of information we've collected will be available to engineers, scientists, and future missions anywhere. In short, there's still a lot to do with LightSail, and that's where you come in. As a member of the LightSail mission team, we need your support to secure LightSail's legacy with all of these projects. Visit to make your gift today. LightSail is your story, your success, your legacy, and it's making a valuable contribution to the future of solar sailing and space exploration. Your donation will help us continue to share the successful story of LightSail. Thank you.

Sarah Al-Ahmed: So when you actually do these tests, I mean barring all the differences between them, what is kind of the structural difference of these craters versus the craters we see on the moon or Mars, something that's less metallic?

Simone Marchi: So what I can say now it's based on this understanding that we're building from experiments. So these are lab scale experiments. So imagine the craters that we're producing are not huge, so you have to keep that in mind When we try to make a comparison, say for instance, craters on the moon or other celestial objects. Those craters are much, much, much larger than what we produce in the lab. So having that said, we can compare the impacts all crater produce in the lab, so we can compare crater produce in an iron meteorite crater produced in a piece of rock. And they look very, very different at the lab scale. And the primary reason for this is because the metal is much, much harder than any rocks. In fact, typically these iron meteorites are hundreds of times harder than any rocks, say a basalt, for instance. So it takes much more energy to break them up and to excavate and produce a crater. Well, that results in two interesting outcome. Well, first it's perhaps the most obvious for the same impact energy a crater on a metallic target is going to be much smaller, obviously, because it's much harder to make a dent. But the other aspect is that the way the material, the metal behave at this high energy event you have to imagine that you ... It's like having an explosion. The material start to flow and move around and eventually produce a cavity, a crater. Well, the way the material flow, it's different. So a metallic material flow in a different way than a rocky material. And so what this bring us to, it's a very peculiar morphology. Some of these craters with metal, if you look at their floor, the bottom part, they contain what I like to call like petal structure, little thin sliver of metal arranged radially in a very symmetric way, which are very nice to look at. But this is something that you will never get in a rocky material. And the other aspect of interest are the rim of the crater itself. In a rocky material, the rim typically it's shallow and it sort of crumbles easily and it collapse easily. While on metal, we find this raised rims that are basically very sharp. You can imagine the metal as it flows and it try to leave the crater. It basically freezes in place leaving the sort of blades sticking out the surface at about 45 degree angles, and they just sits there and they're very hard. If you move them, you try to break them apart, they're not because metal is hard. So all of a sudden, at least at this lab scale, we definitely see weird morphologies. It's something that will be just unthinkable of any other rocky material. Now, as I said earlier, the big question is whether or not this morphology that we see in the lab, it's then applicable to much larger scales on an asteroids. So that is something that remain to be seen.

Sarah Al-Ahmed: Most of the art of Psyche depicts these kinds of jagged almost knife like edges coming out of these cratering situations. Were those images created prior to these tests, or is that still something that we think is the case?

Simone Marchi: I believe the two things were coming together pretty much at the same time, I think that some of those sharp edges that you see in some of these wonderful renderings that we have for the asteroids come from looking a little bit at this early batch of experiments that we did, in fact, where we started realizing this aspect of this raised rim and this petal structures in the floor. So yes, in a way, they came together. So I think that those renderings are still a viable realization of what Psyche might be.

Sarah Al-Ahmed: It occurs to me that it's not just the asteroid itself that needs to be modeled physically by using these meteorites, right? But the things that are actually going to be impacting Psyche themselves are going to be these objects from space. So were you using bullets and things like that to shoot the meteorites, or did you make bullets or projectiles out of other meteorites to get very accurate?

Simone Marchi: No, regarding the impactor that were simply beads, quartz beads. The reason is because it's the easiest thing in the lab to manufacture, and they are well-known in terms of properties, and that provide us with very nice consistent material for these experiments. Now, when it comes to real impacts in the asteroid belt where Psyche is, we can certainly imagine that for the vast majority of the impactors would be rocky asteroids, because that's what's happening in the main belt. Most asteroids are rocky. There are very few asteroids that are not rocky in the main belt. And so the impact of natural will be rocky. So the fact that we use quartz in a sense is sort of, it's not, of course, what we find is space, but it's sort of similar. And one other thing to consider is that the impactor material plays not much of a role in the outcome, in the sense that the impactor is completely destroyed and vaporized upon impact because of the energy. And so the specific nature of it doesn't necessarily alter the outcome, unless of course you go completely wide and you take a metallic impactor, well, that will be different.

Sarah Al-Ahmed: So now we've done all these experiments, we've got these computer models, we have art, we think we know what this is going to be like. But what kind of things do you think we could actually learn about the early Solar System or planetary formation by studying this body?

Simone Marchi: There is growing evidence and consensus I think, in the community, in the Planetary science community that in fact, the main belt, which is a structure between Mars and Jupiter that contains millions of asteroids. All of those asteroids may or a large fraction of them may have formed elsewhere in the Solar System. So that necessary didn't form where we find them today. So a fraction of them could have formed much closer to the Earth and then been implanted into the main belt where they currently are. And likewise, another fraction of them may have formed in the other Solar System and they have been implanted into the main belt. So think about this processes, the main belt is sort of a melting pot of objects coming from all over the place in the Solar System. Now that makes interesting, because how about Psyche? Is it perhaps an object that form there or formed another location of the Solar System? And so this give us a little bit of an opportunity to try to understand the composition and the properties of these objects may reveal some of these early processes of transport across the Solar System. And that's one aspect that I'm particularly interested in. But there are other things as well. Like we mentioned earlier, if this is a core of a differentiated planet, then would give us unique opportunity to study the guts of the interior of a larger object. And that will be a unique opportunity. We stand on Earth, we know there is a metallic core below our feet down in the Earth, but we cannot really see it. And so here we have an opportunity where we can possibly see something like that.

Sarah Al-Ahmed: Wouldn't that be fascinating? I mean, it could tell us a lot about our planet and others having an opportunity to study an exposed planet core might be one of the most, forgive me, metal opportunities.

Simone Marchi: Heavy metal opportunities.

Sarah Al-Ahmed: Does your team make a lot of jokes about that? Because I know we do.

Simone Marchi: Yes, a lot.

Sarah Al-Ahmed: So Psyche is finally out there. We have all these ideas about what we might find when we get there, but it's going to be a little bit, the spacecraft's going to be traveling through space. So what's the timeline there? When can we start expecting the first data coming back from Psyche as it approaches the asteroid?

Simone Marchi: Oh, that's got to be shy of 60 years from now. That's how long it takes to get there. But before then we'll have a gravity assist with Mars. So that will be also an interesting event, and there will be many other things happening between now and then. But regarding Psyche, the first data will come in a little while.

Sarah Al-Ahmed: Just mental image, Psyche cruising by high-fiving Mars reconnaissance orbiter, saying hi to Hope, and then cruising on out into the asteroid belt.

Simone Marchi: Yep.

Sarah Al-Ahmed: What is your team going to be doing in the intervening years as you wait?

Simone Marchi: I bet you can guess the answer. I will be doing more of the impact experiments, that's for sure, because it's fun, because there is an opportunity to learn things that we don't know. And in fact, as we do these experiments, we generate new questions that we didn't even think about it. And so that's been a very interesting twist. And I'm not a lab guy by training or nature, so this is also new for me. So I like it. I like to face new challenges. And so this will be an aspect I'll be interested in. And of course, we'll also plan for all the modeling that's needed in order to interpret what we find on the surface. So one of the things that I'm keen on is to look at the craters, have a good sense of their distribution sizes, that is in fact fundamental information that we can use to then try to infer the past evolution of the asteroids. So for instance, how old is a given surface? We can try to assess that by counting how many craters we have on top of that surface. And with models, we can get to the age question, which is very important. And so all of those things will happen in parallel between now and then.

Sarah Al-Ahmed: I would love to be a fly on the wall during those tests. I'm wondering, have you guys taken slow motion video of these impacts? Because I bet that would be really cool.

Simone Marchi: We actually took fast motion videos.

Sarah Al-Ahmed: Oh, wow.

Simone Marchi: We have cameras that are high speed cameras that can take up to a million frames per second. Can you imagine for each second you have one million pictures that are taken? And that's needed in order to be able to see what happened, because everything is super fast in these experiments. And so that's the kind of instrumentation that we need. Another Ames facility that we utilize for these is equipped with the state-of-the-art high speed cameras. And so all our experiments have been filmed from various angles, various illumination conditions with this equipment. And so yes, we do have wonderful videos that shows what happened in these collisions.

Sarah Al-Ahmed: Are there any places online that people can watch these videos?

Simone Marchi: There might be. I believe some of these videos were shared early on by ASU in some of their outreach activities and blogs and other locations on their Psyche website. So yes, I believe some of them at least are accessible on the web.

Sarah Al-Ahmed: Well, I know what I'm doing after this conversation, googling that. Well, thanks so much for joining me, Simone. This is just an absolutely mind blowing conversation, and I hope you have so many more adventures just firing things into meteorites. That's amazing.

Simone Marchi: Well, thank you so much for having me. It was fun.

Sarah Al-Ahmed: And again, congrats to you and your team. That launch was fantastic.

Simone Marchi: Thank you so much. Until next time then.

Sarah Al-Ahmed: Some people have the coolest jobs. We'll hear from Simone Marchi again in an upcoming show about the Lucy missions rendezvous with Asteroid Dinkinesh. Now let's check in with Bruce Betts, the chief scientist of The Planetary Society for what's up. Hey, Bruce.

Bruce Betts: Hey, Sarah.

Sarah Al-Ahmed: I continue to be amazed by seeing you and other people around the office during our coworking week. It has been a good time getting to see your face.

Bruce Betts: It's been wonderful. It's been wonderful. And now it's over. So go home.

Sarah Al-Ahmed: No.

Bruce Betts: Oh, sorry. Sorry. Didn't ... Okay, nevermind.

Sarah Al-Ahmed: No, it's true though. I like being here in the office, but it won't be the same without all y'all, so. But a good time.

Bruce Betts: It'll be better.

Sarah Al-Ahmed: It'll be better. I'll actually get work done.

Bruce Betts: No, it's been great having the whole Planetary Society staff from all corners of the world. Well, okay. All corners of North America coming together.

Sarah Al-Ahmed: And I just had this kind of awesome conversation with Simone Marchi about firing things into meteorites to test how craters form on metallic asteroids. I mean, that's a wild job.

Bruce Betts: That's so cool. Yeah, yeah. No, I've been friends with people who do impact lab experiments and it's pretty crazy. It's very cool.

Sarah Al-Ahmed: It just never occurred to me that you would need some kind of ridiculous high speed gun with awesome cameras designed to capture the impacts. I understand you have some experience with these tests, not at the same facility but.

Bruce Betts: I'm at the edge of these tests, but not involved in them. So I had a good friend, office mate, who used to do the light gas gun in the basement of the Caltech Planetary Science Building, and I forgot, but they get speeds like five, six kilometers per second, and it's pretty cool noise when they hit all the metal plates designed to slow the target down. And then for impact cratering, that was more studying phase diagrams of various types of iron mixed with other stuff to do planetary interiors. Then you have things like the Ames Vertical Gun, which actually people have done all sorts of experiments over the decades and shooting stuff and watching what happens. It's cool. All I do is throw rocks into a pile of sand. But I love those experiments. And once upon a time, I did some crater studying work on Mars. And so I actually was trying to understand the impact stuff. It's technical term.

Sarah Al-Ahmed: Impact stuff. It's funny because I've never fired a projectile in my life or gone to any kind of range for doing that. But you say, here, come shoot some quartz pellets at some meteorites, and I want to go to there.

Bruce Betts: Well, sure, yeah. We did impact experiments officially and unofficially in my days at Caltech, including cheese.

Sarah Al-Ahmed: Cheese?

Bruce Betts: We did impact experiments on cheese because the whole could the moon be made of cheese thing and hardly sets our justification. Nevermind. Let's move on. What else you got?

Sarah Al-Ahmed: No, no, no, no. Was this for an April Fool's Day paper? What?

Bruce Betts: Oh no, there was no paper.

Sarah Al-Ahmed: That's amazing.

Bruce Betts: Now, turns out the moon not made of cheese. So the research was purely recreational.

Sarah Al-Ahmed: That's hilarious. Awesome conversations about awesome space stuff. I don't know, it feels like a weird point in history to be at this turning point. We're about to go to a metallic asteroid. It might be the core of a planetesimal or something. And here on Earth, we're just celebrating with computer models and firing things at other things and just making awesome art of what we think it might look like. And I bet it's going to completely blow our minds when we actually get to Psyche.

Bruce Betts: This is planetary science. This is what you do. You do what you can on Earth and then hopefully you get a spacecraft going to where you want to go, and then you get your minds blown and you figure out what you got right and what you got wrong. And usually, no matter how hard you work, nature surprises you and you got more wrong than right. But it depends.

Sarah Al-Ahmed: It's funny, because I went into astrophysics thinking, "Ooh, pretty space pictures. I want to focus on this." But planetary scientists, y'all have all the really weird adventures like I'm going to go to Antarctica and collect rocks. I'm going to...

Bruce Betts: Yeah, well some of us just stare at computer screens with them.

Sarah Al-Ahmed: So what's our random space fact this week, Bruce?

Bruce Betts: Well, I'm still stuck on the Lucy mission and things derived from that. So when we're recording this, they're just about to do their first asteroid encounter in the main belt asteroid. But their main goal of the mission is to be the first time studying Trojan asteroids of Jupiter, which hang out 60 degrees ahead and 60 degrees behind Jupiter at Lagrange gravity balance points, but-

Sarah Al-Ahmed: Oh, you didn't actually say random space facts.

Bruce Betts: Or did I?

Sarah Al-Ahmed: Did you?

Bruce Betts: Was it just so fast that you missed it?

Sarah Al-Ahmed: Oh no.

Bruce Betts: Let's redo it just in case, because otherwise, I'll be very embarrassed. Oh, oh, oh random space fact.

Sarah Al-Ahmed: Nailed it.

Bruce Betts: Random space fact is tied to these Jupiter Trojan asteroids. There are a lot of them. There are many, many, at least thousands, if not hundreds of thousands that are over a kilometer or two in size. And they've discovered they're pushing around 10,000 order of magnitude of these Trojans. But the mass, it's like the asteroid belt. The mass is very, very low. And so the estimated total mass, although it's got a typical planetary science factor of two, three error bars, is like 150 mass of the asteroid belt. But wait, the asteroid belt, despite having millions of things, is estimated to have a mass, which have mentioned before of, depending on numbers vary by percent or so, but around 4% of the moon, the Earth's moon is all the mass that's in the asteroid belt and 20% of that in the Trojan asteroids of Jupiter. So there you go. So you're not going to scoop it all together and make a planet is the bottom line, or at least not a very good one.

Sarah Al-Ahmed: You could scoop it together and make one slice of cheese.

Bruce Betts: And I can tell you if you impact that cheese with ... Nevermind. It was cheddar, but there's still a whole open field of research to look at different types of cheeses. But that's not important right now. Trojan asteroids, very cool. We'll get our first view of several of them from Lucy when it gets out there right now in the inner parts of the main asteroid belt.

Sarah Al-Ahmed: And we will be talking to the Lucy team in the future after the flyby. Once they get the first data back and do their first little analysis, we'll have them on the show. So I'm looking forward to that because Dinkinesh.

Bruce Betts: A new world. Woo!

Sarah Al-Ahmed: A new world, new place, new pictures. That's awesome.

Bruce Betts: It looks like a potato.

Sarah Al-Ahmed: They all look like potatoes. We were having a conversation the other day about which planet looked yummiest or which moon looked yummiest.

Bruce Betts: Wow. Io.

Sarah Al-Ahmed: Right? I mean, Io looks pretty tasty.

Bruce Betts: As long as you don't know what it's actually made of. I mean, I wouldn't eat any of the moons, frankly. Just important safety tip for those at home. But Io, it's got that pizza thing going on.

Sarah Al-Ahmed: Right. I feel like Jupiter looks like it would make a really good ice cream.

Bruce Betts: As usual you've thought this through far more than I.

Sarah Al-Ahmed: I have to say we had some really lovely comments on your random space fact last week. People loved the Lucy reference and understanding that name. So one of my members, Craig Griffin, wrote us to say that he loved the Lucy reference and from a space mission to a fossil to a Beatles song reference and to an English woman, like beautiful trajectory. Nice arc.

Bruce Betts: Yeah, no, it's got more of an arc than pretty much any mission name I'm aware of. A lot of good stories. All right, everybody go out there, look out for the night sky and think about Vikings eating Io pizzas and finishing it off with some Jupiter ice cream. Watch out for that brain freeze everyone. Come back next week. Thank you. And goodnight.

Sarah Al-Ahmed: We've reached the end of this week's episode of Planetary Radio, but we'll be back next week with Lindy Elkins-Tanton, principal investigator for Psyche and our partners at the Eclipse Company on their new Eclipse app. You can help others discover the passion, beauty, and joy of space, science and exploration by leaving your review and a rating on platforms like Apple Podcasts. Your feedback not only brightens our day, but also helps other curious minds find their place and space through Planetary Radio. You can also send us your space lots, questions and poetry at our email at [email protected]. Or if you're a Planetary Society member, leave a comment in the Planetary Radio space in our member community app. Planetary Radio is produced by The Planetary Society in Pasadena, California and is made possible by our curious and creative members. You can join us as we nerd out over world's no human has ever seen at Mark Hilverda and Rae Paoletta are our associate producers. Andrew Lucas is our audio editor. Josh Doyle composed our theme, which is arranged and performed by Pieter SchloSser. And until next week, ad astra.