Planetary Radio: Space Exploration, Astronomy and Science - OSIRIS-REx becomes APEX

Episode Date: February 21, 2024

After NASA's OSIRIS-REx spacecraft's successful sample retrieval from asteroid Bennu, it's onto its next adventure as OSIRIS-APEX, the Apophis Explorer. Scott Guzewich, deputy project scientist for APEX, joins Planetary Radio to discuss the next steps for the mission as we count down to asteroid Apophis’ flyby of Earth in 2029. Then Bruce Betts, The Planetary Society’s chief scientist, pops in for What's Up and a look at other multi-world missions. Discover more at: https://www.planetary.org/planetary-radio/2024-osiris-apex See omnystudio.com/listener for privacy information.

OSIRIS-REx goes apex, 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. After NASA's OSIRIS-REx spacecraft's successful sample return from asteroid Bennu, it's on to its next adventure as OSIRIS-APx spacecraft's successful sample return from asteroid Bennu, it's on to its next adventure as OSIRIS-APEX, the Apophis Explorer. Scott Guzach, Deputy Project Scientist for APEX, joins us today to discuss the next steps for the mission as we count down to the flyby of asteroid Apophis in 2029. Then Bruce Betts, our Chief Scientist, will pop in for What's Up and a look at some other multi-world missions. 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. On September 24, 2023, NASA's OSIRIS-REx spacecraft made headlines by delivering precious samples of asteroid Bennu to Earth. This marked the culmination of a seven-year journey that took the spacecraft over 7 billion kilometers, or 4 billion miles. Samples like these are vital to helping us understand the history and future of our solar system, and life on our planet. Our solar system is filled with countless small worlds, asteroids and comets. They're made from the leftover material from the disk of gas and dust that formed the planets 4.5 billion years ago. We think some of these bodies may

have crash-landed on Earth, bringing water and organic materials with them. But to piece together this grand story, we need tangible pieces of the past. And that's precisely what asteroid Bennu offered us. But there's more to this than just a curiosity about our solar system or our planet's formation. Billions of years ago, objects like Bennu crashing into Earth may have been an asset to the development of life. But nowadays, not so much. Asteroids pose a serious threat to all life on our planet. It's actually part of why the Planetary Society was founded. Defending Earth from objects like these is a crucial but complex task, and thanks to OSIRIS-REx, humanity is now far more prepared to tackle these celestial threats.

Now, with the mission to Bennu completed, the OSIRIS-REx spacecraft is setting its sights on another intriguing target, the asteroid Apophis. Apophis was discovered in 2004 by Roy Tucker, David Tholen, and Fabrizio Bernardi at the Kitt Peak National Observatory in Arizona, USA. This asteroid is a stark reminder of the cosmic dangers lurking in our neighborhood. Planetary Society members should be really proud to know that Tucker was a 2002 grant recipient for our Shoemaker Near-Earth Object Grant Program. It funds advanced amateur astronomers who find, track, and characterize near-Earth objects. We may have played a key role in defending our planet, because Apophis is potentially hazardous with a capital H. hazardous with a capital H. On Friday, April 13th, 2029, Apophis will pass as close as 30,600 kilometers. That's 19,000 miles above the Earth. But don't panic. It will not hit Earth for at

least 100 years. Like asteroid Bennu and other potentially hazardous near-Earth objects, with observations, science, and ingenuity, we can absolutely make a plan to safeguard our world from future flybys. But it's going to take work. So, say goodbye to OSIRIS-REx and say hello to the spacecraft's next adventure as OSIRIS-APEX. The origins, spectral interpretation, resource identification, security, a puffus explorer. Joining us today is APEX Deputy Project Scientist Scott Guzage from NASA's Goddard Space Flight Center. Scott has a passion for studying our neighboring planet Mars and near-Earth objects like Apophis. He's at the forefront of efforts to uncover the secrets of our solar system,

but also to protect our world from potential threats. Hi, Scott. Hey, how are you? Doing really well. I'm really excited because I feel like Osiris-Rex crushed it with the sample return. We finally got that TAGSAM container open and got those samples. And now the mission is on to its next phase. How did you get involved with Osiris-APEX? So I got involved, I guess it was probably almost three years ago now when we were still kind of in the proposal stage officially. Some of the OSIRIS-REx team members were kind of rotating off just to focus on the samples themselves and to focus on other work with the primary mission winding down. And so there was an opportunity for new team members to join for

the extended mission exclusively. And this was sort of internal to Goddard, NASA's Goddard Space Flight Center here where I am. And I applied and I was fortunate enough to be selected. Can you give us a brief overview of what OSIRIS-APEX is going to be doing now that it's switched from studying Bennu to Apophis? Yeah, so we're taking the OSIRIS-REx spacecraft, which is an incredibly capable spacecraft with really sophisticated instruments, and we're sending the OSIRIS-REx spacecraft, which is an incredibly capable spacecraft with really sophisticated instruments, and we're sending it to a newer asteroid and one that is going to put on quite a show in about five years' time,

something that has not happened in a long time probably for Earth's history, for human history, and probably won't happen again for a long time hopefully, which is to have an asteroid of this size pass so incredibly close to Earth. And so this is a really unique opportunity. And we're fortunate enough to be able to get the spacecraft there just after it passes by Earth. That's really cool and a great target because this is an opportunity that does not come by very often. From a scientific perspective, it's very exciting, but I'm sure a lot of people are going to be a little scared when this thing comes closer to Earth than our geosynchronous satellites. How was the decision made to redirect this spacecraft to its new target? So after the primary mission, you know, we were sort of on a set trajectory, right? The primary

goal was to get that sample dropped off to Utah. And so the spacecraft was targeted at Earth to make sure it got there and it did. And that all went wonderfully. And of course, the spacecraft started with a certain amount of fuel on board when it was launched. And it used some of that fuel, not as much as it needed to ultimately, as was possibly the case. So it has only a certain amount of fuel left. And so once we kind of diverted past Earth after dropping off the sample from Bennu, it sort of limited the options of what was available. You know, we had this trajectory that we're starting on and we only have so much fuel. So what can we get to with those conditions?

And it ended up being that there was really only two targets available. And one of those was Apophis. And because of the fascinating case of Apophis being so close to Earth in about five years time, it made that decision, I think, really easy. And so Apophis was the one that we chose to target. Well, I'm glad you decided to go after Apophis because this is going to be a really good moment to educate the public, not just about asteroids, but also about planetary defense and why these studies are so important. We've kind of touched on this a little bit,

but what makes asteroid Apophis such an interesting target, particularly considering this flyby in 2029? Yeah, so of course, when Apophis was first discovered, you know, there was a non-zero chance of it impacting Earth in five years' time. And if not then, then maybe kind of in the next time it approaches Earth later this century and next century. Further observations kind of show that that was not really a threat, but it's still passing so incredibly close to Earth,

and it's this really unique opportunity. So it makes it really compelling to study and to see how an asteroid is going to be changed in potentially significant ways by this really close approach to Earth. This is something that we think happens all the time through the history of the solar system. This probably is a really important factor in how asteroids are distributed around the solar system. Seeing this happen in real time, I think, is going to be really, really informative. Understanding how these kinds of asteroids are changed by their past by Earth is going to be really interesting,

especially considering the type of asteroid. I'm sure different asteroids might react differently to that interaction. Yeah, for sure. I mean, Apophis is what we call a stony asteroid or an S-type asteroid, which is the more common type kind of in the near, you know, inner solar system, near where we are. Not kind of like the type that Bennu was, which is a little bit more common farther out. So yeah, it's sort of a very kind of, in some ways, standard case of how these types of asteroids that are approaching Earth,

you know, may pass by. So it should be a really good case study for that reason. As we're exploring these different asteroids, we're finding more and more interesting types of asteroids. I always assumed that asteroids would be more rigid body type objects, but we are finding more and more of these rubble pile type asteroids. Do we know whether or not Apophis is going to be more solid or is it going to be as flaky as Bennu was? We think Apophis is probably a rubble pile of some type. We don't quite know, you know, maybe how it directly will compare to Bennu. Hopefully we'll learn about that when we get there. But yeah, we don't really think from what

we can tell from observations from the ground that Apophis is that sort of rigid, solid body, you know, one big giant stone. It's probably a lot of kind of loose pieces. We think maybe there's sort of two lobes, you know, kind of like that maybe it was two asteroids that kind of like, you know, merged together or kind of slowly combined or perhaps broke apart and kind of recoalesced at some point. It seems that this is a really common thing for asteroids. You know, the kind of closest analogy to Apophis of an asteroid that spacecraft have visited is probably Itokawa, which is the asteroid that was visited by the Japanese Hayabusa spacecraft.

And it was covered with like two lobes as well. So it might be somewhat of an analogy. And then very recently, the Lucy spacecraft flew by Dinkinash and its moon, which we didn't even know was there before, turned out to be what's called a contact binary, which looks like two small asteroids just kind of glued together by the force of their very weak gravity. So this seems to be a really common thing for asteroids. And so Apophis probably is going to be another kind of example of that. That's really interesting because I was speaking with the Lucy team right after that Dinkanesh flyby. And it was really interesting to see that the two lobes on this moonlet were very similar in size. There's got to be some really interesting mechanics going on here that we really don't understand that are causing these moonlets to form in this way.

So it'll be cool to get another close-up view of one of these contact binary objects. Yeah, kind of seeing how they kind of link together and merge and hopefully kind of by understanding Apophis's gravity we can kind of get a sense, like a bit of a picture of what the inside might look like, how that's distributed. So yeah, it'd be very interesting. The spacecraft is actually going to rendezvous with this asteroid after it's fly by Earth, right? So what kind of orbit are we going to go into around Apophis? Or is it going to be kind of like a trailing behind the asteroid kind of motion? It's a few different ways, right? I mean, these objects are so small that, you know, orbit is almost a loose term, right?

Compared to orbiting Earth, orbiting Mars, orbiting Jupiter, whatever the case may be, where, you know, it's almost like station keeping, right? We're just sort of kind of moving around the asteroid in sort of a relative frame. But we're kind of going to approach slowly and sort of study it from a bit of a distance before we get really close. And there's a few different kind of reasons for that. One is to get a good sense of its shape, so we kind of know what it looks like, and can kind of study and optimize our observations and our approach, because we know precisely how Apophis is going to be shaped. And then to understand its gravity field. It's not a regular gravity field like Earth, a round object that's big and massive, right? This is a lumpy, probably irregularly distributed rubble pile, right? So the gravity field is really lumpy, probably irregularly distributed rubble pile.

So the gravity field is really wonky probably, and so we want to study that. So there's kind of a few phases where we kind of move in closely and study these different aspects of the mission and then kind of get into something that maybe is a little bit closer to what an orbit would be like, where you're just kind of going around and letting the asteroid sort of rotate or tumble beneath us. So these different types of motion near the asteroid, do these represent different mission phases that we'll be going through with this close approach? Yeah, we have heard names for these different phases, and they last different durations of time. And probably those may be a little bit flexible based on what we discover as we approach, and we'll refine that over time, over the next few years. But yeah, we kind of have it marked off, you know, a few months at a time

for these different phases and extending over the course of our time around Apophis. Are there any other critical mission phases that you're most looking forward to? So of course, the, you know, what I guess you could call in some ways the grand finale is going to be really exciting. So somewhat like the final sample collection on Bennu, where the spacecraft got down super close to the surface and took the sample and then blasted away. Of course, we can't sample Apophis. Our sample container is back here on Earth in the clean room full of Bennu rocks and Bennu dust. But we can still kind of get down close in a very similar approach just without sampling.

And we're going to approach the asteroid very slowly, get down, you know, really close potentially, you know, just a few meters above the surface. And then sort of blast our thrusters to kind of like back up really fast. And that thruster blast will sort of, you know, excavate or somehow disturb the surface. Of course, we don't know precisely how it will, right? On Bennu, it did a lot more than I think was expected, right? Yeah. It almost created a series of craters kind of around the sampling location because the thruster force was strong enough to really reshape the surface and blast a lot of material off of it. to really reshape the surface and blast a lot of material off of it.

And, you know, is Apophis going to be something like that? Or is it going to be maybe a little bit more cohesive and just sort of expose a thin layer of the subsurface? We don't really know. But, you know, that's kind of why that's at the end of the mission, right? Because it'll be a little bit hairy. I remember seeing those videos of all these pieces of Bennu just flying off everywhere. Yeah. And the spacecraft basically almost got eaten by the asteroid at some point. So it'll be really interesting to see how this works out.

Are we concerned in any way that we might not understand the properties enough and the asteroid might just swallow the spacecraft whole? I'm not worried about it swallowing the spacecraft. We'll keep our distance above the surface. But I mean, I think there's certainly a chance at least that we get showered with some amount of dust or pebbles or whatever other material, as happened on Bennu, right? Certainly there was a lot of stuff that flew back from Bennu and hit the spacecraft, but didn't cause any damage that we're aware of. So certainly that's possible on Apophis as well, right? We won't know, but

that's kind of why it's at the end of the mission, because it's sort of accepting a bit more risk. So we'll just see how that goes. Yeah. I know I read as well that there's a potential that near the end of the mission, we might actually try to land the spacecraft on this asteroid. Is that something that we're actually thinking of doing? It's not in any plan right now, that we're actually thinking of doing? It's not in any plan right now. But I guess it's sort of in a, that would be at the end of a second extended mission,

perhaps, or something like that. So there's certainly things that I think we would probably want to do from, you know, quote unquote orbit or from, you know, from a standoff position before landing. I mean, you could refine the measurement of something called the Yarkovsky force, basically the way the asteroid rotation is changing by the force of sunlight. We could probably get a bit more coverage of Apophis with our instruments, maybe even attempt a second one of these sort

of thruster blast maneuvers. So there's some other options. You know, I wouldn't say landing is excluded, but that's probably, again, the end of a second mission, except for the extended mission before we think about doing that. It'll be really interesting to get some more information on this Yarkovsky effect, but also on the other things that might be disturbing this asteroid's orbit and its spin rate. Particularly as it passes by the Earth, the tidal interactions might do some really interesting things, but the spacecraft isn't actually going to be that close to Apophis during this flyby. So how are we going to be able to figure out how the asteroid was changed during

this event? Right now, kind of ahead of the Earth flyby, we have a really pretty precise measurement of Apophis' rotation just from ground-based, Earth ground-based observations. And we, as in the APEC spacecraft, will be able to see Apophis ahead of when it passes by Earth, but only kind of as like a point source, like a star in the distance, right? But even from that, and that's kind of how a lot of Earth ground-based observations work, you can get a pretty good measurement of the rotation rate and properties of the asteroid from that alone. So we'll be able to monitor that. And so we'll be able to see how that changes ourselves. And of course, ground-based telescopes be watching that very closely as well. But soon after the asteroid passes by Earth, I mean,

really soon, within a few hours, it's going to get too close to the sun for Earth ground-based telescopes to watch anymore. And so, it'll really be down to us, to APEX, to watch this change as it happens somewhat in real time. And then, of course, when we really rendezvous with the spacecraft a bit later, we'll get a very, very precise measurement of its rotation rate and properties. And you mentioned the Yurkovsky effect. So what's going to be exciting is we're going to be able to watch that force change over time, which is the first time we'll have a spacecraft really measure that change in that forcing, that Yarkovsky forcing, versus just sort of measure it in steady state. That'd be really interesting to know as well,

because I've heard people suggest that this Yarkovsky effect, the way that these things are spun up or interact with sunlight, is part of why they might spin up over time and be flinging pieces off that might actually form these lobed moonlets. So this will be interesting not just for that, but also for understanding long-term projections of these things, orbits around the sun, especially for Apophis, because we know it's not going to hit Earth for about 100 years, but that could get a little weird a few years out. Yeah.

I mean, just like at Bennu, being kind of at the spacecraft and knowing its orbit around the Sun much more precisely, because we have a spacecraft there that's radioing with Earth, and so we get a really, really precise measurement of its orbit, that was able to kind of reduce the threat level that Bennu was projected to be. As of all the asteroids we know right now, Bennu is still the most threatening, even though it's a very, very low chance of impacting Earth anytime in the next 100 years. But the same thing will happen for Apophis. We'll get a very, very precise measurement of its orbit, and that'll help us kind of project out into the future where it will be. The longer you go on in the future, the more

uncertain that knowledge can be, just because of the gravity effects of the planets and other asteroids and things like that. But it'll give us the best estimate of that by being at the asteroid itself. That's part of why I'm so grateful for all the asteroid hunters and all of these upcoming satellites. They're going to be helping us track NEOs and other objects, because the more information we have about what's actually in our solar system, the easier it's going to be to do these gravity simulations to figure out where these things are going. Because right now, it's like the worst extreme of a million body problem. Exactly right. Yeah, for sure. We want to know where all of them are and all the time, preferably. Yeah, because, you know, it's been a while since the Chicxulub impact, but we have situations like Tunguska and these things happen all the time.

So it's really important that we know how these objects are up close, because this could potentially be make or break for us when we're trying to deflect one in the future. Sure. Yeah. There was, I mean, even just, I think a month ago or so, there was a very small asteroid that was discovered, I think, just a day or two before it burned up in the atmosphere above Germany, right? I think that was only maybe a small couple meter size object, but we found it just a little bit right before, a little bit before impact, but it, you know, it was small enough it burned up in the atmosphere and was just a pretty impressive bolide from Germany.

atmosphere, and was just a pretty impressive bolide from Germany. We also saw what happened in Russia during that. That was a terrifying situation. And it wasn't that big of an asteroid or a rock. It was maybe the size of a smallish car or something. Thankfully, it exploded before it hit the ground. But even that can damage so much property and hurt so many people. Absolutely. Thankfully, we're going to get to know more about this one before it comes

anywhere close to hurting us, which is great. We're going to be doing this thing where we stir up some of the regolith and see what's underneath. What is it that we can learn about the material properties of this asteroid through this process that we couldn't learn from just looking at it through our observations above it or through spectra? Yeah, it'll help us tell how cohesive it is, right? Is it a rubble pile kind of even on the surface, you know? And that's what Bennu appeared

to be, which was not even expected despite studying Bennu for, you know, a year or more before the sampling. And so we can really understand its material properties of the surface, which is really helpful from like a planetary defense point of view for a kinetic impactor like the DART spacecraft was, understanding how that force would impact on the surface, how that force would then get distributed through an object and then hopefully change its orbit if that was needed. And so that's really informative. And it also will excavate the subsurface material. So we get a better understanding of what the material is like without being exposed to the vacuum of space, being exposed to the really hard radiation

of the Sun and the galaxy, which kind of weathers the surface of asteroids. And so it can throw us off a little bit perhaps about what the real chemical composition and structure of the asteroid is. And so kind of digging down a little bit gives us a bit more of a pristine sample, so to speak, of what the material is like and its chemical composition. You brought up the DART mission and it just occurs to me that I bet

as with the DART mission where asteroid hunters all over the world just redirected all their telescopes to observe that thing. This is probably going to be one of those moments too, where people around the world are going to be trying to observe that thing. This is probably going to be one of those moments, too, where people around the world are going to be trying to observe this.

Is there any way that we can coordinate people's observations, or are there any plans to gather people's data after the fact? I think there are already plans in progress to coordinate a lot of the ground-based, both visible and infrared and radio telescopes, to study Apophis as it approaches Earth. And as I said, the way the geometry works out to my understanding is it's really going to be on that approach to Earth that ground-based telescopes can observe it because really soon afterwards, it'll not be in a very favorable position because it'll be too close to the sun. But yeah, I think there's already a coordination happening to make that

really big effort and study Apophis as it gets close. And then really, it'll kind of be on us, on APEX, to study it afterwards. So I think that collaboration is going to be really fruitful. You've just made another great point about why it's so necessary for us to have these space-based ways of observing these objects. Because on Earth, we're very limited by what we can see that's near the sun. And we can have techniques in space that allow us to block out the sun's light so we can see things better, which is a great thing for protecting us because you never know when something's going to come from the sun's direction right in our faces. Yeah, absolutely. Are there any big mysteries about Apophis that you're personally hoping that we can

solve through this mission? I'm particularly interested in the planetary defense aspects of it. I think this is because Apophis is something that's approaching so close, because it's a very common type of near-Earth asteroid. In some ways, it's the most typical case of an asteroid that would threaten Earth perhaps in the future sometime. I think understanding those properties and helping to provide a way or different ways that we could divert an asteroid that's threatening Earth that's like Apophis in a

lot of ways in the future, I think that's where I'm personally excited to see the data that we collect and what we can do to inform those strategies. I'm also really excited about being able to compare what's going on in this asteroid with a lot of the others because there are so few of them that we've been able to get close to. There are several over our history, some asteroids and comets, but we're finding with a lot of these, as with Bennu, that they're very carbon rich, maybe with a lot of interactions with water. We haven't got all the results from the samples from OSIRIS-REx yet, but this is sounding like it might have less

interaction with water. It might be a very different kind of substance because it's so stony. So it'll be interesting to compare all these objects and where they're located and where they're from in our solar system to kind of get a better sense of how our solar system evolved. are located and where they're from in our solar system to kind of get a better sense of how our solar system evolved. Yeah, absolutely. It seems, you know, we've visited now, I can't remember off the top of my head, but you know, a dozen or 20 some different small objects around the solar system. And every single one seems to be different, even if they're sort of the same class, you know, as observed from Earth, but they're all seem to be very unique. And that makes it really fascinating.

So even though we've been to asteroids of the same type with spacecraft before, I don't think there's any doubt that Apophis will surprise us in some way and be different than those other ones. They always surprise us, though, don't they? I mean, as you said with Lucy, they did not see that moonlet coming. But I believe that mission is going to be visiting 11 different asteroids, most of them Trojan asteroids. We've got some other missions coming up from some other nations as well that are going to be visiting. So the number of these is about to jump up dramatically in the next decade or so, which is really exciting. Yeah, for sure. For sure.

There's enough differences between these objects that I imagine you might need to be using the instruments on OSIRIS-REx, now OSIRIS-APEX, a little differently. Are there any calibrations or any changes to the ways that you're going to be using these instruments? Yeah, a couple of ways. So first of all, because when we sampled Bennu, we blasted a lot of dust up. And so the spacecraft is kind of coated in a thin layer of Bennu and including on a lot of the instruments. And this was studied and already kind of calibrated to some degree while at Bennu because we knew, okay, we're kind of looking through Bennu material to see Bennu. So what does that do to change the data and how can we sort of subtract that? So we're just studying

the true surface of the asteroid. And so that's something that's already ongoing and it will continue all the, you know, between now and when we arrive at Apophis. And that's something that's already ongoing and it will continue between now and when we arrive at Apophis. That's something that is understood pretty well. The second aspect is Apophis is just a much brighter asteroid than Bennu. Bennu is very dark, this sort of coal black surface. Apophis, both by the nature of where it is and just its material, is going to be a lot brighter for the instruments. And so all things being equal, we would want to kind of look at a Paphos for a shorter amount of

time than we did a Bennu to get the same data, right? So imagining like you're looking at a bright flashlight versus a dim one or something like that. But that's again, pretty easy to understand and to change. And actually that's where having the Bennu dust covering the instruments actually helps a little bit because it attenuates that light a little bit as it comes into the instruments. That's a really cool thing to know because I was concerned given how bright this object is, it might limit your observation time or you might accidentally burn out your CCD chips or something if it's too bright. I've seen people do that on telescopes and it's brutal. Yeah, we have a good idea of, you know, the changes that will be necessary.

But it'll be something, again, that's sort of probably fine-tuned a little bit once we get to Apophis. How is this mission going to tell us more about the relationship between stony asteroids and meteorites? Yeah, so we think that the S-type asteroids, of which Apophis is a member of that sort of asteroid class, is very similar to one of the most common meteorite types that we have on Earth. The S-type asteroids, of which Apophis is a member of that sort of asteroid class, is very similar to one of the most common meteorite types that we have on Earth. These are what we call ordinary chondrites. In fact, the samples that were returned from the Itokawa asteroid by the Hayabusa spacecraft, their study basically finds that the materials are very similar to ordinary chondrites.

We think Apophis is going to be something similar to that. But again, when you kind of observe something in space versus when it's passed through the atmosphere and it's been changed in some way by that experience. And again, everything's a little bit different, right? And having it in space, there's that weathering effect I mentioned. So being able to observe a substance in its sort of natural environment, which is the vacuum of space versus on the ground, and comparing those, I think, is valuable. And so we'll be able to do that with APEX. We'll be right back with the rest of my interview with Scott Gusej after this short break.

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It's very rare that we get a sample back from somewhere. And it can be very challenging to figure out where these meteorites come from, given that we don't know the chemical properties of things like apophis. Exactly right, yeah, for sure. I mean, there's a wide diversity in the meteorite catalog. And then we observe these asteroids in space and also see diversity of spectral types and the way that they absorb and reflect light in different portions of the spectrum. And so, again, being able to kind of space truth that data is something that is one of our goals with the mission.

If this is some kind of rubble pile stony asteroid, do we think that pieces might actually be disturbed off the surface during its flyby Earth? Could the tidal effects do that? It's possible perhaps for some of the smallest grains. We don't think half the asteroid will rip off or anything like that. But one of the most surprising things at Bennu was that there were these small particles being ejected from the surface. That's one of the things we will actually look for when we arrive at Apophis, both for the scientific interest in that and also just for the spacecraft safety point of view.

We don't want to be in range of these little pebbles being shot off the surface if that's happening. When Apophis does the close flyby of Earth, we will be pretty far back. So there's no risk to us at that particular time. But yeah, studying that change will be really interesting. And certainly the gravitational torque of Earth could disturb the surface in some way. And that's one of the things we're going to look for after we arrive. What other things do we think these tidal interactions might do to this asteroid? So two things that we know very well just from sort of modeling is that it should change the rotation rate of the asteroid. And it's also going to change the orbit, you know,

very significantly. So both Apophis and the APEX spacecraft are essentially doing Earth gravity assist, like any number of our spacecraft do all the time when they want to go out to Jupiter or Saturn or anywhere else. And so Apophis' orbit is really going to change dramatically by this close passage to Earth. And then again, its rotation rate, basically the length of its day is going to change as well. So both of those we know will happen very well. And again, we'll refine that with the spacecraft observations when we get there.

And then we're kind of looking to see, you know, is the surface modified in some way? You know, is there seismic shaking that has sort of smoothed out regions of the surface or disturbed, you know, boulders and that sort of thing? We're going to look as closely as possible to see if that has happened. How quickly does it currently spin? It is a pretty slow rotating, but it's what we call in technical terms non-principle axis rotation.

So it's sort of tumbling. It doesn't have one fixed axis like Earth or Mars or even Bennu. It's sort of tumbling in this complicated rotation rate. And that rate is going to change yet again when it passes by Earth. I'm wondering whether or not the asteroid's actual orientation as it flies by Earth is going to have any real effect on how the Earth will affect it, right? any real effect on how the Earth will affect it, right? Because if it's some kind of blorpy double-lobed object that's facing one lobe toward Earth versus sideways, that could make a difference.

Yeah, I think there's some uncertainty, obviously, because of that orientation aspect that you're mentioning as to how its final state will end up being. So yeah, it'll be really interesting to see. Right now, we have a solid idea of where this object's going to be for about the next 100 years. We can say it's not going to hit Earth. But do we have any idea of how much this flyby is going to help us refine that understanding of its long-term hazardous nature?

I can't put a number on, you know, how much farther out with whatever accuracy we can predict once we get our data. But it will, with what we know already, we think Apophis is going to pass through kind of what's called a keyhole of some size. And it's pretty small now, right? It's only maybe a few kilometers in size. And we'll get that down to even finer precision when Apophis passes by, both from the ground and from apex observations. And then we'll be able to track it closely over the time that we're at the asteroid. And so that will refine that prediction of the future orbit significantly. But I can't tell you how much kind of farther out into the future we'll be able to predict. But the close

flybys to Earth, I think, again, happen in another 50 or 60 years and then another 50 or 60 years after that. I can't remember quite the cadence, but it's a ways out there still afterwards. I'll imagine what our capabilities will be then. I mean, 50 years ago, we were just landing the first humans on the moon and look where we are now. I'm sure we'll figure out a lot in the meantime. How do you think that this mission and its study of Apophis is going to help us with our future planetary defense strategies? I think it's going to help a lot. I mean, I think there's a lot of possible defense mechanisms that have been proposed,

you know, the Armageddon way, right? Send a nuke to it or the DART kinetic impact way. And there's been even some more sort of subtle ways that have been proposed utilizing the Yarkovsky effect, for example, almost painting an asteroid and having it reflect more light and doing a very slow modification of its orbit over years and decades and centuries. I think by having APEX there, understanding its physical properties, both its cohesiveness, its material properties, its bulk density, and then just the physical chemistry and geology of the surface will inform a lot of what effect these different mechanisms, these defense mechanisms would have on an asteroid like

Apophis. And again, like I said, Apophis is a pretty typical example of the type of asteroid that could be threatening to Earth at some point in the future. And so I think, you know, that really excellent data that we're going to collect is going to help kind of tell us which one of those mechanisms might be better in different circumstances or how far in advance will we need to kind of know which mechanism to choose. That type of information, I think, is going to be really valuable. organism to choose. That type of information I think is going to be really valuable. I like the idea of trying to use the Yarkovsky effect to alter these asteroids trajectory because we can do something like dart it, blow the thing up, but who knows how long it will be before that thing reforms. If we have these rubble pile objects just going around the solar system, we're going to need some extra data on how hard you have to explode it so the pieces don't come back together again. Whereas we could just send up a

spacecraft to just spray paint one side of the asteroid. Yeah, yeah, there's a lot of different ways, right? And it's the brute force method versus these really sort of gentler methods, so to speak, that maybe just take a lot longer to kind of have the effect. But when you're talking about an object that's maybe threatening us in decades or centuries time, you just need a tiny, tiny little nudge at the right point in time. And that can be enough to kind of shift it off the path so it's not going to be a threat. If it's kind of in that last final days or weeks, then we're a little bit limited in our options, right?

Because the spacecraft has a lot of inertia when it's coming in on orbit. And to move it or disturb it in some way takes a lot more force. You mentioned earlier that cosmic rays and other radiation from space can alter the chemical makeup, but also the coloration and stuff on the outside of these asteroids. Is there enough difference from the inside to the outside that we could perhaps use this Yarkovsky effect by simply brushing dust off the surface of one side? That's a really interesting idea. Yeah, I don't know. It's worth thinking about.

Yeah, and it probably depends too on the chemical makeup, right? The inside might not be bright enough for... One of the things we'll hopefully be able to figure out is how deep do you have to go? The regolith on asteroids is, the term people use is gardened, because these small micrometeorites and tiny little bits of other asteroids are constantly hitting and churning up the surface of any object in space, whether it's an asteroid or the moon or whatever. How deep do you have to go to

get a bit more pristine sample that's not been exposed to the vacuum and radiation of space and has not been affected by this micrometeorite gardening over whatever timescale you're speaking about? So hopefully kind of doing that maneuver at the end with our thrusters will help kind of tell us how deep do you have to get to really kind of see that different coloration, that different makeup. That'd be cool to know, too, because who knows if these rubble pile objects are kind of churning over time.

And that could be fascinating. You talked a little bit about this earlier, that we might maybe at an extended, extended mission try to land on the surface of this thing. But there are some other activities that we could do after this November 2030 end of missions. Are there any activities that you think we should definitely try to accomplish if we get that extended, extended mission? So the one thing that's really kind of low effort, and we've talked about already, was extending the observations to refine that estimate of the Yarkovsky effect. So it's one of those things where the longer you're sort of at the spacecraft and can observe that effect, it's a really, really tiny force.

And so the longer you can sort of integrate that observation lets you kind of refine that precision down to smaller and smaller numbers. And so just adding a few months or a year to that observation, again, which really doesn't require much more than the spacecraft just sort of sitting next to the asteroid, would really kind of beat down that noise and let us have a much more precise estimate of the Yarkovsky effect on Apophis. Some other things we could do is just kind of continue to extend the coverage with our instruments, right? Our cameras and our spectrometers. Because Apophis is in this tumbling sort of orientation, it's not going to be like

Bennu or even our observations of Earth or Mars, where a spacecraft can just kind of sit back and let the object or the planet rotate underneath of us, and you know you're going to see the whole thing. Because Apophis is tumbling, there could be these really kind of weird effects where we just keep missing one spot, right? Because where we are and where the asteroid rotates just kind of don't link up properly. And so if we're, hopefully by November of 2030, like you said, we'll have a good understanding of, hey, we've got this coverage in this part of the asteroid, but we're missing this one place, or maybe we want to go back to this one place and get a bit more data. And so those sort of options would also be kind of top of our list, I think. I'm flashing back to the European Space Agency's Rosetta mission. And when they were

looking at Comet 67P, Churyumov-Gerasimenko, and they were trying to find the Philae lander for ages, that little lander was lost. And then right near the end of that mission, they finally found it on a place that they hadn't been able to observe before. Who knows what we're going to find in those last days and weeks of the mission, especially if there's places that are hidden from us. That's really cool. This is way far out. But if you in your dreams could like come up with the final landing place or the final resting place for OSIRIS-APEX after all this time in space, after all that it's done, what do you hope would be the final resting place for the spacecraft? I mean, I think it would be so cool if we could have the fuel to send it to another asteroid, but that won't be the case. We won't

have enough fuel to really leave and go anywhere after our mission. So the spacecraft is going to end near or on Apophis one way or the other, right? It's just the effect of limited gas in the tank and gravity will ensure that. So we'll end up near Apophis one way or the other. And I think, you know, hopefully kind of doing science as long as the spacecraft allows us would be my hope. And we'll see what happens. We've got a first extended mission to accomplish, and I think it'll be great. And then we'll go from there afterwards.

It'd be really funny if it managed to stay close enough to this asteroid that eventually someday when the asteroid swings back around, we can go snag OSIRIS-APEX out of there. There you go. And we'll return that to Earth. Yeah. It would deserve it. I was just speaking with Matt Golombek, who worked on all the Mars exploration rovers recently, and talking about the ways that we could potentially memorialize these things years and years, even maybe centuries in the future. These artifacts of human space exploration are all over our solar system, and we're going to have to treat them lovingly.

Otherwise, I bet space pirates are going to get them. Do you have any plans for the actual Apophis flyby? Like, are you going to fly out to Europe or Northern Africa to go see this thing? Are you going to be in mission control? Yeah, I have not thought about that yet. So just for the listeners, I mean, unfortunately, for those of us in North America and South America, the Western hemisphere, it's going to be daytime when Apophis does its close flyby. So it's not going to be visible to us. It's only going to be visible in the nighttime sky to Europe, Africa, a good portion of Western Asia. And so that's going to be the place to be if you want to look up in the sky and see Apophis flying by. I floated the idea of us going on a Nile cruise that day. I don't think that has

gone anywhere yet, but we'll see what happens. I think most likely I'll be back here at the office getting our data and preparing for a rendezvous a few weeks and months later, but it's fun to dream. Yeah, I've been lucky enough to actually do that cruise on the Nile. And I'm just imagining what that would be like at night with this potentially terrifying, but also absolutely awe-inspiring event going on overhead. I hope you guys get to do that because that would be amazing. But either way, I'm really looking forward to this. And I'm really hoping that this is going to be a moment that really makes us all reflect about our relationship with asteroids and near Earth objects, because we can pretend

that this isn't something we have to be concerned about. We can even laugh at movies like Don't Look Up. But it's only inevitable that one of these days, one of these things is going to come our way. And these are the missions that are going to really help save humanity. Yeah, absolutely. Yeah, I think it's going to be a really great opportunity to communicate with the public and understand, yeah, our place in the solar system, right? And that we live in an active and dynamic solar system. And it can be a dangerous place, but it also can be a really exciting place to visit and study. Well, thanks for helping us do

this kind of study, Scott. And for everything that this mission is going to do, it's going to be a few years until we get to give the really cool updates, but I'm looking forward to those images. Yeah, me too. Thanks, Sarah. When I was a child watching movies like Armageddon and Deep Impact, I was absolutely terrified that a rock from space was going to take away everything that we love.

It makes me feel a lot safer knowing that people around the world are working together to track, characterize, and potentially deflect objects like Apophis. Life is scary enough without the threat of asteroids and comets taking us out like the non-avian dinosaurs, so I hope it helps you sleep at night. There are scientists around the world working to keep you and everyone you love safe. Now let's check in with Bruce Betts, our chief scientist for What's Up. Hey, Bruce. Hello, Sarah.

How are you today? I'm doing fine. I don't know why I'm talking like this. Part of the human experience, Bruce. Being weird. Wow. You're a weird one. It's just part of the human experience.

Don't be alarmed. Speaking of things that are outside of the human experience, nice segue. Ooh, segue. Ooh, but I think it's really, really cool that OSIRIS-REx is now OSIRIS-APEX. It's really smart that we already have this spacecraft. It's already done its thing. And then they figure out a way to continue to use it and then send it off to another world, in this case, Apophis. Yeah. Those orbital dynamics people,

they're crafty. Right. Get things done. And this was great because we'll see what else, if anything, we can get to Apophis. But at least we have this, a very well-equipped spacecraft. We have this, a very well-equipped spacecraft. We'll be checking it out shortly after encounter. And that's great. And it's what few other spacecraft have done. Of course, lots of planned such things. But Stardust did this after encountering their comet. They brought back samples, dropped them in Utah, because that's where we drop samples.

And then, or the U.S. anyway. And then they went off and checked out the deep impact missions comet and saw the crater that was formed by that years before and they redirected that after their main mission was done so it's super cool and they have enough reserve fuel to to be able to do this along with the crafty redirects. I'm a big fan of such clever use of existing functional hardware and teams that are together to get more use out of things, since the tough part is getting it built, getting it up there, and getting it working. So if you can keep it going, you're likely to keep it going.

That's profound. That is profound. The fact that we can have spacecraft that can strategically maneuver to actually visit more than one world is really cool to me. The only one I can think of that was designed to go into orbit around multiple worlds purposefully was the Dawn mission to Ceres and Vesta because it had those cool ion thrusters. But we've still managed to do things like New Horizons, flying by Pluto and then out to Arrokoth. Yeah. Another analog where they completed their primary mission and then

thought, hey, what can we do with the fuel we've got? And theirs was trickier because they had to tie it to a whole campaign to try to find something in the cone that they could hit with the fuel they had. And they found the perfect snowman. Do you have a favorite multi-world mission? Oh, I love them all, just like my sons. I love them all. I mean, there aren't that many, and clearly Voyager 1 and 2, although all flybys were the... I mean, Voyager 2 did the master stroke of doing four worlds and an orbital opportunity that only happens once every 175 years, I believe,

to be able to use gravity assist from one to the next. So that alone is pretty awesome, and it still gives us our only close-up views of Uranus and Neptune. So that would be pretty high on the list. Obviously, Don doing clever orbiting of two different worlds and being able to study them in detail. You can go back to the first uses of gravity assistant going world to world. Mariner 10 actually was, I believe, first, and it did dip by Venus, did a little science, a little testing, and then gave us our first and only views for many decades of Mercury up close. So also kind of a throwback favorite.

And I'm sure I've missed a few, and they're all awesome. Stardust, now this. It's good. One planetary body is good. Then two, great. Three, awesome. Four, we're looking at you, Voyager 2. Actually, you know, we've also got a larger, much larger number of things coming up with Lucy.

Yeah. Lucy mission is on its way, and they actually upped the number along the way. So they threw in another flyby that they did and found the cute little binary asteroid system. Oh, Dinkinish. And so I believe they're 11. Oh, right, because they cleverly put on their website that now their mission goes up to 11. So they have 11 objects scheduled. That's so cool.

We've got to dial it up to 11 on all these worlds because there's so much left, so much left to explore. Yeah, but it goes up to 11. This is a bit of a weird and spicy question, but how do you think the world is going to respond when Apophis flies by Earth? earth? Well, this is not my expertise, but I'd say it's safe to assume not the same. Not all few billion humans will respond the same. So you will get people, including all of our listeners and members who are just super psyched on it and learning about it and drinking up as much science information. You'll have people just go, whoa, that's so cool. That happens? And we're hoping, turn this into a lesson of, hey, that came close. We need to keep working so we can actually prevent the impact of an asteroid doing major catastrophic damage, which is one of the big foci of the Planetary Society is planetary defense and doing that.

And then you'll have the stuff that I will find annoying. And that is the people who don't believe it's going to hit Earth, the people who think it's a conspiracy, the people who think that I was the one who directed the asteroid and it actually will change at the last minute and hit Earth. Now I'm already mentally prepping myself for all the articles that are like, Apophysis is coming. Panic. It's Bruce Betts' fault. My job is done. All right. What is our random space fact for this week? Random space fact.

Beautiful. So, sample return. Moon, astronauts. You probably wanted to get a feel for how much rock and dirt was brought back by all the Apollo missions from the moon. And, of course, the way to do that is to turn to one of our favorite sports. to do that is to turn to one of our favorite sports. So the mass of rocks and dirt brought back from the moon by astronauts in the Apollo program is about equivalent to 21 granite rocks or stones used in the sport of curling. Oh, wow. That's more than I thought it would be. Those things, they slide down the ice, which depending on where you live are called rocks or stones. They range from 17

and a quarter to about 20 kilograms or 38 to 44 pounds. And you'd have to throw together about 21 of those on average. That's so awesome. I had a really good time when I was working at Griffith Observatory. We had a piece of moon rock there. Of course, I didn't get to touch it or anything because it was behind several layers of encased glass. But it's still cool being that close to a moon rock. It's true. Way back in the Dark Ages when I did lab spectroscopy, I played with lunar soils. They're not actually soils. Any live person on Earth will tell you that.

Lunar regolith, lunar dirt. and it's just pretty profoundly weird. Whenever I talk to geologists and stuff like that about rocks, it's usually some question about, like, did you lick the rock? But I would not want to lick a moon rock. Like, I'm sure the regolith is sharp. Yeah, the particles are actually a problem for exploration because they are small and sharp and get in everything. Yeah, weird. That's why I only have a geology minor on my PhD. You didn't look enough rocks, Bruce.

All right, let's take this out. All right, everybody, go up a fair. Look up, look up, look up in the night sky and think about dolphins as they move through just beyond the surf at the beautiful beach, relaxing setting and occasional as they blow air out and exhale. Think of that. Thank you. Good night. We've reached the end of this week's episode of Planetary Radio, but we'll be back next week to commemorate the 20th anniversary of the Red Rover Goes to Mars program. We'll be joined by two former student astronauts who experienced life-changing opportunities when they applied to the program.

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