Planetary Radio: Space Exploration, Astronomy and Science - Lucy's first asteroid flyby reveals a surprise moon

Episode Date: November 29, 2023

On Nov. 1, 2023, NASA's Lucy spacecraft, which is on a mission to investigate Jupiter's Trojan asteroids, made its first flyby of asteroid Dinkinesh. Hal Levison and Simone Marchi, the mission's principal and deputy principal investigators, join Planetary Radio to discuss the asteroid rendezvous and the surprising discovery of Dinkinesh's moon. Stick around for What's Up with Bruce Betts, the chief scientist of The Planetary Society, as he digests the discovery. Discover more at: https://www.planetary.org/planetary-radio/2023-lucys-first-asteroid-flyby See omnystudio.com/listener for privacy information.

Lucy flies by its first asteroid. 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 Lucy spacecraft, which is on an epic adventure to investigate Jupiter's Trojan asteroids, passed by its first asteroid called Dinkinash. Hal Levison and Simone Marquis, the principal and deputy principal investigators for the mission, join us this week to discuss the surprising results and the spacecraft's health. Then Bruce Betts, the chief scientist of the Planetary Society, joins me for What's Up and some more asteroid awesomeness.

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. NASA's Lucy mission launched in October 2021 on a journey to explore Jupiter's Trojan asteroids, a group of celestial bodies that share Jupiter's orbit around the Sun. To understand why these asteroids stay in place relative to Jupiter, we need to talk about Lagrange points. Most space fans have heard of them in the context of science fiction, or perhaps when you're learning more about the placement of space telescopes like JWST. Lagrange points are like sweet spots in space, where the

gravitational forces of two large bodies, like the Sun and Jupiter, balance with the orbital motion of a smaller object, like an asteroid. There are five of these points, called L1 to L5. Jupiter's Trojan asteroids are mostly found near two of these points, L4 and L5. They're 60 degrees ahead of and behind Jupiter in its orbit, and in all of these years of exploring, we've never seen one up close. Lucy is the first dedicated mission to explore Jupiter's Trojan asteroids, which may contain the primordial materials of our solar system. Just in case you're wondering, the Lucy mission is named for the famous fossilized

skeleton called Lucy, which completely advanced our understanding of human evolution. This mission mirrors its namesake's purpose not by telling us more about human history, but by seeking to unveil the solar system's origin story. On November 1, 2023, after two years in the sky with diamonds, the Lucy mission reached its first asteroid, the main-belt asteroid called Dinkinish. Its primary targets are still a few years away because it's a long way to Jupiter. But right out the gate, Lucy's first flyby was a wild success. As the spacecraft flew by Dinkinish, which some people are lovingly

calling asteroid Dinky, it discovered something surprising. It turns out the Dinkinish system isn't one object. It has a moon, and that moon is a contact binary. There's a lot to unpack here, but we have the perfect people to tell us more. Our guests today are Dr. Hal Levison and Dr. Simone Marquis. Hal is a scientist at the Southwest Research Institute and the principal investigator for NASA's Lucy mission. His research covers a broad spectrum of subjects. He works on the formation and evolution of solar system bodies, including terrestrial and gas planets, comets, Kuiper belt objects, and Trojan asteroids. He's also the co-author of SWIFT, which is a widely used software package for orbit integration

and solar system studies. Broadly speaking, he works to understand the early dynamical evolution of the outer solar system. Our other guest is Simone Marquis, who you may remember from the October 25th episode about modeling craters on the metallic asteroid called Psyche. Well, he's back. Simone is the deputy principal investigator for the Lucy mission and also works at the Southwest Research Institute as a staff scientist. Simone focuses on the bombardment history of our solar system by analyzing craters on terrestrial planets

and asteroids like Dinkinash. Thanks for joining me, Hal and Simone. Hi, Sarah. Hello, Sarah. It's great to have you both back on the show. I know I spoke with you just a few weeks ago, Simone, but Hal, you haven't been back on this show for two years. It's been quite a while, so thanks for joining us again. My pleasure. for two years. It's been quite a while. So thanks for joining us again. My pleasure.

So when last we left our heroes, that was both of you, how the last time you were on this show, you had just set your eyes on the Lucy spacecraft for the last time before it was off on its adventure. And now it's cruising through space. So what has this last two years been like for you and the team? It's been a rollercoaster ride because we've had a problem with one of our solar arrays, which didn't deploy properly. That has been very stressful getting through that. We think we're through that. And then, of course, we had a flyby of Dinkinash, which I can be honest to tell you that I thought would be boring as hell.

It's just a little tiny main belt asteroid, and it turns out to be really fascinating and exciting. So it really has been an up-and-down trip. It has been. And I'm glad that you brought up the solar arrays because I remember that moment. We were all watching the live stream for the Lucy spacecraft launch, and then just a few days later to get that word back that the solar arrays because I remember that moment. We were all watching the live stream for the Lucy spacecraft launch. And then just a few days later to get that word back that the solar arrays were having trouble deploying. We were all very nervous. So how did you actually manage to try to deploy

these? Because my understanding is that they unfold kind of like a Chinese fan and that it just didn't latch. So you guys did a lot to try to make that work. What were your attempts? Well, the pull harder is basically all we could do, right? The way these things deploy, as you say, it looks like a fan unfolding, and there's a lanyard that's on the end of one of it that's being pulled by a motor. First of all, and I have to say, the team was absolutely amazing. We learned about this the day of the launch. And frankly, we didn't know whether we could fly the mission for quite a while. And it took about a month, maybe six weeks of a lot of work of very talented people to figure out just from a little bit of data. We just had basically one plot of current versus time on the motor, figured out what

happened, and came up with a plan of how we could get it to deploy more. Full deployment, because it unrolls, is 360 degrees. We were about 330 degrees. We turned the motor on, you know, run it for short periods of time, let it cool off, run it again, let it cool off. Did that several times during our redeployment attempts. And we now believe we're at about 355 to 357 degrees. The array is not latched, right? But we've gotten it about as far as we can. And we think the array is going to be structurally sound enough to be able to fire our main engines, which is the biggest stress. The first time we do that is in February. That's good to hear because you've got so many targets you have to navigate between. And the

first question in my brain was, even if we get it deployed most of the way, it might get knocked back a little bit if we start firing those thrusters. So fingers crossed. Yes. The other aspect of this problem is that these arrays are made out of cloth. So the way you get structural strength is by having them under tension. And the one is not under as much tension as it should be, right? So the spacecraft is floppier than we expected. That led to us having to redesign all the control systems on board the spacecraft. Lockheed Martin has never done that before. So again, that was an

amazing effort by talented people to redesign the control systems and do it so we could still do Dinkinish. And this is a big moment. I mean, there are so many targets you're going to fly by, but being able to do this first flyby and really test the systems will tell you how healthy the spacecraft is. Simone, you just recently saw the launch of the Psyche mission. You're also working on this one. So it's been a jam-packed few weeks, few months for you. What was that flyby day like for you and the rest of the team? I think it was just an amazing experience. Every time we fly by an asteroid, we don't really know what we are going to see, right? As much as we can prepare and have tried to visualize what might happen, but reality is that we don't know. And

sure enough, there is always room for unexpected things to happen. Now, in this case, I have to say that it wasn't just simply fly by an asteroid with a spacecraft that we already, you know, used in the past for similar events in which everything has been tested. And so there was lots of uncertainties. And we were doing this for the first time, also building on what Hal said. We were also concerned some of the performances of the spacecraft because of the conditions that we have with the solar arrays and such. There were lots of expectations and not knowing precisely what we will get out of this flyby. And that was really a motivation to add this to our already

rich list of targets, really with the idea of testing the system as soon as possible to find out if it works as expected. And so there were many things. And it's not just the condition of the spacecraft, also the way the spacecraft keep tracking over the target as a flyby. So there were many things that we were interested in testing at once. And so this was really a great, a great opportunity to do all that. This is such a small target. Of the asteroids we visited, this thing is so small. And you're testing all these systems on board.

Were there any unique challenges to try to get so close to an object this small? And what did it tell you about the health of the spacecraft? There were challenges, right? There were challenges, right? In particular, as Simone said, we were trying to test our system that see the targets an hour away or a couple hours away, this one we could only see it within a few minutes of close approach. And so the system had to be fine-tuned to actually respond very quickly and didn't have a lot of time to actually use the word think about, but you know what I mean, about where to point and how to point. And it worked absolutely flawlessly.

It absolutely did because the images that we got back were very startling for such a small body. This is really cool that you pulled this off. Can't disagree. Indeed. What's interesting about this is that, you know, it's on its way to go visit the Trojan asteroids. We're not there yet. It's going to take us a few years to actually get there. As you said, I didn't expect this to be the most spectacular test ever.

But as you got the images back from asteroid Dinkanesh, it revealed all these interesting things that we didn't expect. So what was that discovery process like for you and the team as the images came back? Most of the things were gathered in the morning when the actual flyby was taking place down in Lockheed Martin in South Denver. So we were monitoring for what's possible during the real-time event what the spacecraft was doing. Once we got confirmation that things seemed to be fine regarding the spacecraft, then we moved back to our office in Boulder. And then we had the science team gathering and looking at the screen. Basically, there's a white screen in front of you, and you're just counting the seconds until the first picture comes up. That basically is what it was.

And lots of expectations and trying to guess what it might be, but there is no real way of imagining this. And the funny thing was the first picture we saw was a little bit from far away, not one of the closest approach, and these objects look weird. I mean, it was a completely weird shape, and we were really scratching our heads because it didn't make much sense. And things started to clear up a little bit with another picture because a part of the body was actually moving independently from another part.

Well, it turns out that was a satellite. You know, you can imagine all this was great excitement for seeing this and eventually the highest resolution picture came down. And lo and behold, the satellite was there, but also lots of details on the surface. So we have lots of pictures that were taken during that day with basically our mouse kind of open in miring what was on the screen in front of us. That's how it went. My exploration of it was mostly through images coming off of social media. So as they were revealed one at a time, I was like, oh, there's a moon. And oh, that moon is actually some kind

of contact binary object. And it just got weirder and weirder. When did you guys realize this moon actually might have been two objects kind of smashed together? It took overnight, actually, because the data that showed the post-close-approach images, where you could clearly see the contact binary, didn't come down until the next day. So we knew there was a satellite. That was very exciting. That was not totally unheard of. There are certainly many objects of the same size as the Ganesh in the near-Earth object population that look a lot like this, the top-shaped primary and the little satellite next to it, right? So that wasn't totally shocking.

It was exciting, but not shocking. And then the next day, we get down, the images post close approach where you could really see the secondary well, and we noticed it was a contact binary. And that, I can't imagine anybody would have expected that. And no one in the room certainly did. I must admit, I still don't know how you make it. But that just sort of blew our minds. There's a great picture when that moment came down with all our mouths sort of open in shock. I haven't seen that picture yet, but I have to look it up because I feel like I did the same kind of shocked Pikachu face as I was looking at that image. Because really, how did that thing form? Clearly, either they all formed together

in one system or somehow this moon was captured by Dinkinash. But at some point, they were all completely different objects. And that's just, that's a lot for one flyby test. Well, we don't know, right? There's certainly a lot of models that have been done that use, invoke a spin-up of the object that, due to radiation effects from the sun, that when the object gets up to spin speeds that are really fast, material will come off the equator and end up forming a satellite. And indeed, these objects all have ridges on the equator, and Dinkin-Nesh does have such a ridge. So you might think that things formed together, I mean, formed in that way. The challenge is how you get two objects,

and if you do, why are they the same size? That's saying there's something in the process. Let's say you formed two objects this way and they just came together. That says there's something in the process of the formation that likes a particular size object over other sizes. And none of the models that I'm aware can explain that. So the real key here is we have two objects of the same size. And I don't think any of the models can predict that. That's so fascinating. So strange. And already, this mission is throwing us for a loop when we didn't even expect it to do it at this point.

Did we have any indication from the light curves from the data that it might have been some kind of binary object before we got there? Do you want to talk about that, Simone? Yeah, that's a good question, Sarah. Yes, indeed. We had been gathering light curves for our target for quite some time. And in fact, since we made the decision to fly by Dinkinash, then we started an observational campaign from the ground. And so we had built a light curve, which if you look at it, it looks, you know, it's similar to many other light curves, and we thought we

understood it. And so the light curves gives us an oscillation of light that reflected, that was interpreted to be simply due to the shape, uneven shape of the object as it rotates. Now, by doing that kind of analysis, you get a period for such a rotation for the object, you get a period for such a rotation for the object, which was 52 hours, similar to many other asteroids, hundreds of other asteroids that have similar light curves and similar periods. So there was nothing really super peculiar about this light curves that was gathered from the ground. And so we were going in with this event, having a sense of, I would say, security in terms of understanding what was going on. This probably was an object, uneven object with a spinning period of 52 hours. You know, it's not that complicated. Now, of course, that was terribly wrong in the end. And we started

realizing that there was something that was not really making sense. In fact, a month prior to the flyby, that is where we started taking light curves data from Lucy instead of from the ground. So that's where we were approaching our target. That is done typically for navigation purposes in order to refine where the position of the object is in space and so we can have a flyby as planned. And so in taking all that data, we also built a light curve and the light curve was showing a behavior that would not make much sense with what we measure from the ground. Now, a key difference was our approach was coming from a very different angle that had seen from the Earth. And so, the fraction of the surface that

was illuminated was very different than what was seen from Earth. And so, that could mess up a little bit interpretation. But still, we were really, it was a puzzle we couldn't reconcile the light curve from the spacecraft in approach with the the ground-based light curve and that is the time where i believe we sort of started thinking well maybe there is something different going on maybe we didn't understand everything and maybe it's because there is a satellite. I have to say, honestly, at some point we were betting, you know, what you think is there is a satellite, because I wasn't quite convinced. I said, well, I'm not convinced that the data shows us there is a satellite,

but if I have to bet, I'll say 50-50. And, well, of course, eventually there was a satellite. And now that we are going back and reanalyzing all the data, I think we have a way to make sense of everything. So I think things are coming together in this regard. Let me just add one thing to what Simone said, because it's a cautionary tale. There has been a lot of work by a lot of people over decades taking light curves of asteroids and interpreting them in the way we were interpreting the ground-based observations. And this just shows that those interpretations are wrong. A lot of what we think we know about the shape of asteroids is probably incorrect.

Given that we had data before and now it's completely surprised us, are there any other targets that Lucy's going to be flying by in the future that we think might be these kinds of binary objects when we thought they were initially just one? Probably not, because in addition to taking light curve data from the ground, we've had a comprehensive campaign of doing stellar occultations. And this is going out into the field when one of our targets moves in front of a star and watching the star blink out.

And from that, you can actually get real shapes and sizes of our targets and we've done that for all our targets we have a lot of data so we really to zeroth order understand the shapes of our Trojan targets and so I don't expect there to be a surprise we may discover a satellite or two. I think there has to be another satellite in our first Trojan encounter called Everbetis. But for various reasons, I think there's another satellite there. But I don't think we're going to be surprised again like this for the Trojans. again, like this, for the Trojans.

Now, remember, we have a second main-belt asteroid encounter with an object called Donald Johanson, and it has an extremely strange light curve. And interpreting that is going to be, I mean, I just don't know how to interpret the light curve we're seeing. It's very high amplitude and very long period. And I wouldn't be surprised if we see something similarly weird, right, at Donald Johanson when we get there. Yeah, and we already know satellites for some of our Trojan targets.

So in a way, we are a little bit ahead of the process, right? Because we have discovered, the science team, Lucy's science team has discovered a couple of satellites. One is for Uri Bates, our first Trojans, and the other one is for Polymer, our second Trojan. So we already know that we are dealing with satellites. Now, as Hal said, there may be more hidden somewhere, but we'll have to see. At this point, what I find most puzzling about this, as Hal said, this light curve is simple, and we thought we understood it. And clearly that was wrong in this specific case.

We thought we understood it. And clearly that was wrong in this specific case. And so that brings you to the point of what we really know about other small asteroids. There may be lots of weird things that we can't really imagine because we don't have good data enough. And the only way to solve this problem, there are two, right? One is to send a spacecraft, which is very expensive. But the other is through doing these stellar occultation campaigns, right? And so I think this is sort of indicating that perhaps the community should invest more in doing these kind of campaigns. Because what we thought we know, we clearly don't.

We'll be right back with the rest of my interview with Hal Levison and Simone Marquis after the short break. Greetings, Bill Nye here. How would you like to join me for the next total solar eclipse in the Texas Hill Country this coming April at the Planetary Society's Eclipsorama? country this coming April at the Planetary Society's Eclipse-O-Rama. That's right, I'll fly you and a guest to Texas and you'll have VIP access to all things Eclipse-O-Rama, talks on astronomy, planetary science, captivating exhibits, star parties, and more. To enter, go to eclipsewithbill.com. Donate $10 or more for your chance to win. You don't want to miss this because the next Total Solar Eclipse doesn't come through here until 2045. So don't let time slip away. Enter today and good luck. We're only at the beginning of doing something like this. I mean,

this is the first time that we're sending a mission to a bunch of Trojan asteroids. I'm sure that we're going to learn things that we can't even begin to predict at this point, which is so strange. And I wanted to ask about this too, because with a lot of previous asteroid missions, we've gotten there and found that these objects are very rubble piley, very not the texture that we expected. As we flew by Dinkanesh, what did we learn about its composition and maybe how fluffy or rigid it is? Well, it's still early days to have definitive assessments for what we have found. We're still going through the data and analyzing it. But a couple of things are sort of emerging. First is the surface, the overall structure of the objects. We're still in the process of building up a shape model of what's

needed in order to do detailed investigation of how the shape of Dinkinish compare with other similar size asteroids. And so we are still preliminary. But the shape is interesting in a way that, at least to me, it doesn't look like a simple rubble pile asteroid. There are structures that we see. There is a chunk that seems to be missing on one side. And on the other side, there seems to be a big trough going through. And then we also clearly see some craters on the surface, although not many craters, but some are clearly visible.

And for instance, if you compare with other asteroids, say Bennu or Ryugu, for instance, their shapes are quite different than what we find for Tinkinesh. And also for those asteroids, it was really a challenge to find even a single crater on the surface. Nothing was really super obvious. Well, we see obvious craters on the surface. So that seems to indicate that there are differences in the bark properties and internal structure, perhaps. But it is still a little bit early days to find out precisely what the differences are.

Well, cratering is your whole jam, Simone. So I'm wondering, the fact that it has craters on the surface, does that indicate that it's probably a more rigid body? Because otherwise, my brain tells me it might fill in those spaces a little more easily. Well, the first thing, when I saw a crater, I said, oh, good. So I have something to do. Jokes aside, but it was nice to see craters. I don't necessarily think that it would imply to have, that the object has higher strength because of craters. I mean, you can have craters in a pile of sand, you know, with no whatsoever strength,

or very minimal internal strengths or frictions, and you can have craters that way as well so i don't necessarily think that craters indicates that so we'll have to see once we have all the data and also shape model would be important for instance to to get to the question of what the shape is of those craters or the shape may reveal for instance if if there is lots of regolith of loose particles on the craters themselves, or if it's more, you know, sort of more rigid object. One thing to look for, for instance, in that regard is the depth of the crater with respect to the size of the crater. That's typically used as a measure of how much regolith there is on the surface. So all of that,

it's something that needs to be done. So we'll have to see for a proper answer to your question, Sarah. But I think that the fact that we have craters don't necessarily imply it's high strength. Well, the data has only just come back. We're only just beginning to learn these things. What other mystery is the team still trying to puzzle through in this data? team still trying to puzzle through in this data? We're really at the point of just looking at the data and getting a first order understanding of what's there. We're not really to the point where we can even speculate. We clearly see this equatorial ridge. We see these cracks and things like that. We're in the process of thinking about, well, this feature overlaps that feature, and what's that tell you about the history? But I can say there's a lot of data there, and let's say unlike OUIGU and BNU,

and I think eventually we're going to be able to put together a pretty detailed story of what happened to this object. Well, I'm glad. I'm going to need a little 3D model to add to my collection on my desk eventually when we know what its full shape is. And thankfully, your team has several, well, at least two years until your next target flyby. You have time to go through this data, but what does the future hold? What does your next few years look like before we get into the good stuff? Well, I mean, we have several events before the 2025 Donald Johansson encounter. We, as I said earlier, we're turning on the main engines for the first time on the 31st of January. That's going to be a big day for us because we really have, although we've modeled the spacecraft as well as we can,

how it's going to behave in space is still a little uncertain. That is going to be a high stress day to make sure it behaves the way we expect it to behave. Then in December of 24, we have another Earth flyby. Remember, we're covering a lot of space, and we actually are using Earth gravity assists to target our Trojans. So there are three over the history of the mission. We had one last year, and we're going to have another one. We're not going to be taking any data, unlike the first one, during this encounter because the geometry just isn't favorable. But we're going to have to work through that detail. And finally, right, you know, we are, I mean, I must admit,

this is getting more intimidating the more we work on it. If you remember how busy the time of the Pluto encounter was with New Horizons. We have four such encounters in 15 months. So the way we're handling that is we're doing all the planning now. There's still a tremendous amount to do in just planning the encounters at our science targets. in just planning the encounters at our science targets. And so it's going to be a busy time, even though you may not hear a lot from us over the next couple of years.

Well, that's really a great point, Hal. And I would like to stress that because people outside the team may feel, oh, there is all this space between one event and the other, all this time, you know, and so you can relax. But I have to say that there is really no time to relax in a sense, because there is always an important activity. It could be the planning, as Hal said. In fact, you know, building the sequence, observational sequence and the planning for future flybys or EGAs or maybe there is a new asteroid to fly by. All of that is taking all the time we have and the team has been great at both the engineering side and the science team to support all these activities, you know, one after the other.

Is that a conceivable situation where you decide on your journey that you might want to get a little closer to another asteroid on the way? Well, we certainly did it now with Dinkin-Nesh. That was mainly put together because, as we said, it was a test of our systems, right? And from an engineering point of view, the best philosophy is if you're going to fail, fail sooner. And although Donald Johanson is also a test, it's going to be testing different things. But we decided that it was worth going after this. And let me just take a step back. The amazing thing about this encounter is if we had done nothing, we would have flown within 64,000 kilometers of Dikinish. That's 20% of the distance from here to the moon.

So we were getting close anyway. And so it required very little resources, right? resources, right? I don't think we have the time to add another encounter between now and the end of the first set of Trojan encounters in 2028. It's just going to be too busy. Even if we found something we were flying by, we just don't have the time to design another science sequence, you know, tweak the trajectory to get there and to be able to do it, particularly if it's Trojan because all those encounters are very close together, right? There is the possibility if we were to find something after we leave the first group of Trojans, which are in the leading L4 swarm. And then we have six years before we get to the trailing swarm. And if we

found something there, we might consider doing that. But that's so far in the future that it's not even on our horizon. Plus, you know, you're already dealing with a situation where the solar panels or the solar arrays didn't deploy perfectly. So conserving energy and conserving fuel when you've already done these tests is probably a good plan. I'm just really glad that of the tests that you did, it was Dinkanesh because we got this very strange situation there. It could have been the most boring rock ever, but it wasn't.

What are the odds? Well, I think the way to interpret that is that none of them are boring. That's probably the thing. And being weird is common. Of the targets that you have coming up once you actually get to Jupiter's Trojan asteroids, which ones are you both personally most looking forward to? I think they're all exciting for different ways. And it's really hard to pick one.

But you know me, you know that I like collisions and cratering and smashing things. And so if I have to pick one, I will definitely pick Uribates, which is the first Trojans that will fly by. The reason being Uribates is the largest member of an asteroid family. And so we think that, you know, the family is formed by catastrophic collisions of larger asteroids that was blown apart. And then you generate a bunch of smaller ones that are the family. and enduribates is the largest remnant. And so this will be the first time in which we fly by an asteroid that is the result of

a catastrophic disruption. And so I have a great expectation because of that, because maybe it can tell us a little bit more about how catastrophic disruptions work. And we know that that's sort of a fundamental process, evolutionary process for asteroids in general. So that makes it very intriguing. And now on top of that, there is also small satellite cata around Uribates. Well, maybe that is also the formation of that is also related to the formation of a catastrophe, you know, the catastrophic disruption, to the permission of the catastrophic disruption, perhaps.

And so there's lots of little mysteries like that. And plus, by looking at craters that we find on the surface of Eurybates, we can possibly pinpoint when this catastrophic disruption took place, right? By observing how many craters there are on the surface, which will be also an important constraint for the evolution of the Trojans in general. For all these reasons, I would pick Q-ribates as my favorite. What about you, Hal? Is it the same one or a completely different one?

No, it's the totally different side of things. You know, my interest has been understanding how planets form and evolve. And that includes forming the first macroscopic planetesimals in the solar system. And there's reason to believe, and I can go into this, but it'll be a long discussion if you want, that two of our objects have their primordial shapes. One is Polimeli, which is our second Trojan. By the way, that only happens like 30 days after everybody, so we're going to have two back-to-back, right? And it is shaped like the object Arrokoth, or the large lobe of Arrokoth, in the sense that it is essentially hamburger-shaped. And we can understand that through models of the formation of the first planetesimals,

but it's unlikely to arise in objects that have been broken apart. So this indicates, suggests that it's primordial. The other is at the end, in 2033, we're flying by a near equal mass binary. There's also reasons to believe that it's a nearly primordial object. The objects that are the oldest and leftover from the earliest stages of formation are the things that fascinate me. And those are the two objects that you can point to in our stable of Trojan targets. That would be really interesting to know whether or not those are actually just kind of untouched remnants. Because the things that it could tell us about the formation of planets and other asteroids in our solar system is just kind of unfathomable. I feel like we're just at the beginning of this whole new discovery age. But we actually have to get to these asteroids first in

order to look at them up close in order to figure it out. So you guys have some really exciting years ahead of you, is all I'm saying. I think so. I mean, I think we have to emphasize that, you know, and I say this in my talks, this is really a mission of exploration. These targets have never been seen up close before. And not only that, not because of their proximity to the orbit of Jupiter, small things leaving these swarms can't get to the Earth. Jupiter will accrete them before they can evolve into an Earth-crossing orbit. Unlike other small body reservoirs, the main belt, the comets, we don't have any meteorites from these objects.

They're really a mystery. Do you think there's anything about the Trojan asteroids that might really surprise us? Anything about their composition? I don't even know how we'd begin to guess at that, but there's probably a lot about those specific asteroids and their formation that makes them very distinct from other asteroids. that makes them very distinct from other asteroids. Yeah, I think that's right. There's lots that we don't know,

and it's hard to imagine what it might look like, but composition is one of the things that I would say is least understood for these objects for various reasons. So Hal said earlier, right, we did occultations of our targets, and occultations give you a good sense of shape. Certainly, it's not high-resolution shapes like we would like, but at least they give you a sense. But when it comes to composition, these objects are, for the most part, and I'll clarify what that means, but for the most part, are featureless.

So if you take a spectral data, you do not see clear absorption bands like, for instance, you would see on Vesta or Ceres or many other main belt asteroids. And if you don't have those absorptions in the spectra, then, you know, it's hard to say what they're made of. And so we don't really know much about their composition because of this. Their spectral properties are relatively featureless. Plus, they're very far from the sun. They're small. And so they are dark, meaning their magnitude, it's limited. And so also the spectral data, most often than not, it's very noisy.

It all builds to the fact that we don't really know much. But these objects likely formed in the outer solar system. So you would think that in a way or another, they might contain ices, maybe water, CO2 or other species. They might contain organics. So all of that mixture, you know, how it's that precisely what's the makeup, we don't know. We hope that as flying by with our spectrometers, we can definitely get a better sense of that. We may start seeing absorption features on these objects that could tell us, you know, the composition. And so I suspect that that is going to be one of the areas of investigations that will be particularly important for the Lucy mission.

It's just really beautiful that we finally have a spacecraft that can begin to explore these things. And I'm sure it's going to open up so many more questions than we're even prepared to answer at this point. So I'm sure that you're going to have some really, really exciting years. And hopefully, in a decade or more, when we finally have information back from all these, I'll hit you guys up again, bring you back on the show if you're willing. It'll be our pleasure.

Yeah, that'd be great. Well, good luck to you and your team. I know it's going to be all of us kind of waiting on the edge of our seats for years, not getting to see all of the craziness behind the scenes. But it sounds like you're all going to have to put in like 110,000% to get this all done. So good luck to you and everyone. And seriously, congratulations on this flyby. This was beautiful. Thank you.

Thank you. I'm serious, though. If you find a 3D file for Dinkanesh or its adorable mini-moon, please email it to me. I'll put it on my desk at Planetary Society HQ right by my model of comet Churyumov-Gerasimenko.

Okay. Now let's check in with our chief scientist, Bruce Betts, for what's up. Hey, Bruce! Hey there for what's up. Hey, Bruce. Hey there. I love this, that we thought we understood what was going on, but we clearly knew it could surprise us. Then we got there, and as usual, it surprised us. And, you know, even after learning that this asteroid had a moon, it just keeps getting weirder.

And I wonder what we're going to find as Lucy continues to travel out there. Probably weirder and weirder, and I wonder what we're going to find as Lucy continues to travel out there. Yeah. Probably weirder and weirder things. But it definitely justifies. I often discuss our Shoemaker-Neo grant winners that are really advanced amateurs, sort of. I mean, they're just really good. And part of what they do is put the telescope time into doing light curves that will sometimes show you that something's a binary. that will sometimes show you that something's a binary. Because if something's coming to Earth, you kind of want to know that.

But even the little guy's a couple hundred meters, I think, which will really ruin a lot of people's day if it came this way, which that one won't, but we need to find others. Sorry, got off on my planetary defense kick. No, but that's the important thing. We need to preserve and protect our planet, right? We need to make sure that we're not going to get completely beamed. And, you know, there's only so many asteroids that we've actually visited so far.

So this is going to up the number by quite a bit. Who knows what we're going to discover. They've turned it up to 11. They actually are making the joke themselves. I love that. Because they started, they had nine, and then now they've got 11-ish. So they turned it up to 11. But that's amazing. That's unprecedented. And also, they'll be showing us the Trojan asteroids for the first time, Jupiter's Trojans that are in front and behind it. And I mean, you know, they probably look like asteroids, but hey, let's find out. But what kind of asteroids, right? Like, even as a kid, I thought they were solid, chunky objects. And now it turns out most of them are these rubbly piles of, like, just debris kind of loosely chilling out with each other, which is not what I expected as a kid at all. Well, not many people expected that not that long ago.

And then we started thinking that there would be these so-called rubble piles. And I'm hoping for a fluff ball, which some people theorize. And then you got your pretty solid metallic metal ones. Metal. And there's a lot of variability in the asteroid population, which is another reason it's good to study it both as many as you can get remotely and then do these missions out there to them. Because it's interesting science, because what the heck's going on? And then also for planetary defense. What are the fluffball ones like?

Are they kind of more like particulate kind of conglomerated together? Yeah, just smaller fluff instead of boulders. Cool. But I mean, they're not at all like cotton candy, but I think it's more fun to picture them that way and pink. That is more fun. I used to make cotton candy at fairs when I was in Girl Scouts. So now I've got a real clear image.

Thank you. We did have a question that I wanted to put to you from one of our commenters. Because I know a lot of people are in this mental space where they've only recently learned that the International Space Station is going to be coming down at some point. And a lot of people want to know what we can do to help preserve the International Space Station. And specifically, one of our listeners wrote in, his name is Victor Carr. He wanted to know what it would take to try to boost the International Space Station to maybe lunar orbit or something like that and why we shouldn't try to accomplish that. So I wanted to put that one to you since you are the chief scientist.

Why should we not attempt that? That would require some serious rocket power because you've assembled this over tens of missions to get all this stuff up there and put it together. And so the amount of mass, which isn't on the top of my head, top of my brain, tip of my tongue, something, it would take a lot of rocket power or other techniques, but rockets are probably the only practical one on a reasonable time scale. And so it would cost a lot of money. It would cost a great deal of effort. You'd have to design new rockets.

They'd have to not damage the station, which is not designed to undergo stresses of sticking rockets on it. And so just generally, especially boosting it to a lunar orbit would be – fundamentally, it would be incredibly technically challenging, incredibly expensive even. You can figure it out. And remember, we have a limited budget, unfortunately – well, I mean realistically for space stuff. So if you boost the International Space Station to the lunar orbit, you don't do a whole lot of other things. Yeah, it's a tough call, though. I mean, we have that every program we get and people fall in love with the hardware

and then the hardware, you know, you move on to something else. And because of the budgetary limit, typically you have to kind of end one, especially hugely expensive program like ISS, to be able to do hugely expensive other programs, particularly in the human program. to be able to do hugely expensive other programs, particularly in the human program. And they deteriorate over time, so they're not as fresh, and you don't get that new space station smell when you go to it. I mean, not even now. God knows what smell you get now.

Oh, man, I was reading a paper the other day about the weird bacteria and the particulate buildup and the air in there. I bet it smells funky in there yeah okay maybe it won't go okay whereas i bet the the tiangong space station that the chinese national space agency sent up i bet that one's like very nice i mean looking at the images very crisp and clean in there it's beautiful probably. Probably. But that, you know, that new space station smell goes away surprisingly fast. You can buy those little air fresheners, but it's just not the same. When we create the lunar gateway, we should, you know, take a sample of the smell and then make a scratch and sniff of all the different space stations. Wow.

Space station scratch and sniff. That is disgusting. I like it. Love it. All right. Now we can do a random space back so this is a little this is truly random because it's just something I do that helps me when you hear the degrees of latitude on a planet or a moon or you're coming up with distances. And so a degree of latitude on Earth defines nautical miles to use unfortunate but practical units for people off doing nautical things. One minute of latitude, a 60th of a degree defines a nautical mile, and there's 60 nautical miles on Earth for a degree. There are about, so,

and that's about 69 statute miles, but if you're just doing, you just like doing some more rough calculation, 60, 69, whatever. Well, why would I focus on miles and Earth? My gosh, what is wrong with me? Because the interesting thing to me, being a Mars head, is there's 60 kilometers roughly per degree on Mars. There's both the number 60, so it's easier to remember. And then if you're on the moon, divide that by two, and it's 30 kilometers per degree latitude.

Again, approximately. So 60 miles-ish for Earth of a degree latitude, 60 kilometers on Mars, 30 kilometers on the moon. There you go. So something truly random has helped me over the years of staring at maps and figuring out how far things are without getting into details. That's actually really useful. I mean, it's not like we can use it to navigate the seas of Mars anymore. But, you know, if you want to figure out how to navigate a map on the moon or if you're one of the people looking for the one piece on Earth, you can use that. You're talking pirate anime

again, aren't you? I am, I am. Yeah, okay. All right, everybody. Go out there, look up at the night sky, and think about whether the term dry land is redundant. Thank you, and good night. We've reached the end of this week's episode of Planetary Radio,

but we'll be back next week to discuss the largest Mars quake in recorded history. I've been looking forward to this conversation for a long time. You can help others discover the passion, beauty, and joy of space science and exploration by leaving a review or a rating on platforms like Apple Podcasts. Your feedback not only brightens our day, but also helps other curious minds find their place in space through Planetary Radio. You can also send us your space thoughts, questions, and poetry at our email at planetaryradio at planetary.org.

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, Thank you. Paoletta are our associate producers. Andrew Lucas is our audio editor. Josh Doyle composed our theme, which is arranged and performed by Peter Schlosser. And until next week, Ad Astra.