Planetary Radio • Feb 06, 2019

The DART Mission: Learning How to Swat Dangerous Asteroids

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Nancy Chabot

Planetary Chief Scientist at Johns Hopkins Applied Physics Lab, and Coordination Lead for DART

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Bruce Betts

Chief Scientist / LightSail Program Manager for The Planetary Society

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Mat Kaplan

Senior Communications Adviser and former Host of Planetary Radio for The Planetary Society

Why did the dinosaurs die? They didn’t have a space program! The upcoming DART mission will test our best thinking about how we may someday deflect a Near Earth Object that is speeding toward fiery Armageddon on Earth. Nancy Chabot of the JHU Applied Physics Lab is the mission’s Coordination Lead. The Curiosity rover has reached an exciting new region of Mars. Senior Editor Emily Lakdawalla will give us the lowdown. The night sky is full of treasures according to Bruce Betts. Join Bruce and Mat for this week’s What’s Up.

DART approaches the Didymos system
DART approaches the Didymos system Image: NASA / JHUAPL
DART concept poster
DART concept poster Image: NASA / JHUAPL

This week's question:

How long was the longest Skylab mission (the longest that humans were onboard in one continuous stay)?

To submit your answer:

Complete the contest entry form at or write to us at [email protected] no later than Wednesday, February 13th at 8am Pacific Time. Be sure to include your name and mailing address.

Last week's question:

What planetary spacecraft (not Earth-orbiters) were launched by a Space Shuttle?


The answer will be revealed next week.

Question from the January 23rd space trivia contest question:

What was the last human mission to end with a splashdown in the Atlantic Ocean?


Apollo 9 was the last human mission to splashdown in the Atlantic Ocean.


[Mat Kaplan] [00:00:00] Smacking an asteroid to save planet Earth this week on Planetary Radio.

Welcome. I'm Mat Kaplan of the Planetary Society with more of the Human Adventure across our solar system and beyond. The dart spacecraft will leave on a suicide mission in a couple of years. It will slam into an asteroid called Didymos in the first real test of how we might deflect a future object headed toward destruction of a major city. Or, Worse.

Nancy Chabot is at the center of this planetary defense test. She’ll tell us all about it. And why the study of small bodies like asteroids and comets is so fascinating. Later we’ll join Planetary Society Chief scientist Bruce Betts for a look at our busy sky. A look back in history, a more or less random space fact, and a new space trivia contest.

The Mars Science Laboratory Rover has entered a new region [00:01:00] of the red planet. Senior Editor Emily Lakdawalla is here with a preview.

Welcome back Emily. The news that you have for a from Curiosity is so fresh. As we speak, our blog post is not even published yet. So fill us in on why this is such a big deal.

[Emily Lakdawalla] Well, the big deal is that Curiosity just drove onto clay. And that may not sound like a very big deal but it is a very big deal to the mission. When the Mars community got together, for years before they ever launched Curiosity, they selected a landing site where they figured they could find evidence for ancient habitable environments. And Curiosity has actually already done that. But the main piece of evidence, or one of the most important pieces of evidence that led them to pick Gale Crater, was the signal of a certain kind of clay that they could see from space. Clay is a mineral that forms when you attack lava-like minerals with water. It has a lot of water stuffed into its crystal structure. And so the fact that they can see this particular type of clay mineral from [00:02:00] orbit using Mars reconnaissance Orbiter data just filling this Valley at the foot of Mount sharp made them say, aha! We're pretty certain that this crater once held a habitable environment. Lo and behold the mission has found many different types of habitable environments and Gale crater over the many years that it's been operating on the surface. But it's still really thrilling to get to this particular spot where they can compare what they saw from orbit with what will hopefully be a pretty rich trove of clay minerals on the ground. And a new and different kind of ancient habitable environment where possible Mars bugs could once have lived.

[Mat Kaplan] So what's next? You expect them to do some drilling anytime soon.

[Emily Lakdawalla] Absolutely. So they just finished about a year-and-a-half spent on top of what used to be called hematite Ridge. It's now called Vera Rubin Ridge. They drilled four times in that particular area and now they're down off the Ridge and they will be tootling across the landscape and drilling every time they encounter a different type of material.

They'll probably drill at least four [00:03:00] times in this particular material as they traverse across it. Always, they'll be seeking to go up section to begin by looking at how the two different types of rocks relate to each other. Whether there's a smooth transition between one type and the other or whether there's something that a geologist calls an unconformity. Where there's evidence that rocks were exposed at the surface and then new material is laid down. Then they're going to go up section uphill. They're going to cross layers and layers and layers and try to read what those layers record of Mars’ changing environmental history as they go upward through time as recorded in the rocks.

[Mat Kaplan] Very exciting stuff look for this at It should be posted not long after this program appears on the 6th of February. And before we leave the red planet, Emily, you also posted something on February 4th. A little update from Insight involving that chainmail skirt that we've talked about before on this show.

[Emily Lakdawalla] That's right. They finally got the wind and thermal shield down on top of the seismometer. [00:04:00] So now the seismometer is all protected from the elements and ready to do its best possible science on the surface. So the next step there, now that the skirt has descended from the cover and is now shielding the instrument well from wind, they're going to be deploying the heat probe device. And once they've got that on the surface, then there's going to be a long period of waiting while the little mole, self hammering mole inside the heat probe, pounds its way down into the Martian surface.

[Mat Kaplan] Mars, we will come to know you better and better and better. Emily, thanks again.

[Emily Lakdawalla] You're welcome. Mat.

[Mat Kaplan] That's our senior editor at the Planetary Society — Emily Lakdawalla — also the editor-in-chief of the Planetary Report. And we call her our planetary evangelist.

It's hard to believe that it has been more than a month since my trip to the Johns Hopkins [00:05:00] Applied Physics lab in Maryland. You regulars know that I was there for more than the main attraction: the thrilling flyby New Horizons made of Ultima Thule. I also sat down with APL planetary scientist, Nancy Chabot.

Nancy loves everything about our solar system, but she gives most of her professional attention to so-called “small bodies”: asteroids, comets even moons.

She led NASA's SBAG — the Small Bodies Assessment Group — for several years. SBAG, planetary defense, and a Japanese mission to the moons of Mars, all came up in our conversation, but it's Nancy's work as coordination lead for the DART mission that we focused on. Like New Horizons, DART is led by APL.

Nancy, thank you very much for joining me here. It's my last day at the Applied Physics laboratory and I'm getting this wonderful opportunity to [00:06:00] talk to some of you who — maybe you’re proud of what New Horizons is doing — but you have involvement with so many other missions that are underway here. So thank you for taking a few minutes to join us on Planetary Radio.

[Nancy Chabot] Well, thank you for asking me and I'm really glad that we could host you here at APL. It's always great to have people come in and hear about the work that we're doing here.

[Mat Kaplan] It has been a blast and as I mentioned to you, it's my first time here. And I certainly hope not the last. You must, as somebody who is going to play a major role in a mission that has been talked about from the stage here another APL Base mission — You must be pretty pleased to see not only the tremendous success of New Horizons, but just the tremendous record of success that this lab has achieved for so many years. It's got to make you feel good about what's coming, which is the DART mission that we’ll talk about.

[Nancy Chabot] Oh, yeah. I mean APL has really contributed along with other a lot of other institutions to advancing [00:07:00] planetary science and exploring whole new worlds that we've never seen before. The New Horizons and counter has been a great success and I'm really looking forward to the images coming in and seeing all of those and what the future is going to hold for these other missions.

[Mat Kaplan] Well, we do have a lot of stuff to talk about but let's start with DART. The, let me see if I get it right: the Double Asteroid Redirect Test?

[Nancy Chabot] Redirection test.

[Mat Kaplan] Redirection test. I'm close. I'll get in trouble because, as you know planetary defense, that's a really big deal to those of us at the Planetary Society, but perhaps should be to all of humanity — since as the boss says, Bill Nye, and so many other people — why aren't there any dinosaurs? Because they didn't have a space program.

We do! But this is really a first, isn't it?

[Nancy Chabot] It is! And it's exciting ‘cause NASA's planetary defense coordination office was only formally established in 2016. And they've got a whole overall strategy that's very important and [00:08:00] DART, the Double Asteroid Redirection Test mission, is just one component of that larger strategy. It's taking that first step to demonstrate some technology of what would you do if an asteroid was on course to hit the Earth.

[Mat Kaplan] Yeah. We've talked very frequently with people from the planetary defense office as you implied. They are also about finding these things, characterizing them, figuring out which ones are going to cross the pass of Earth and making them near-Earth Objects, of course.

But when I talk about this being a first. This is really the first time we're setting out to see if we can nudge one of these, right?

[Nancy Chabot] That is that that's correct. It's the first mission that really is going to demonstrate some technology and do this test. It very much is a test and it's just the first step of trying to nudge an asteroid out of the way if it was coming here. So thinking about exploding it or destroying it or anything: that's the wrong picture to have. This really is something that you would do years in advance, you know, at least five years, but more like 10 [00:09:00] or 20 years would be even better. Where you would just hit the object hit the asteroid just a little bit and it would change its its course ever so slightly, but then that would add up over the years such that it missed the Earth.

[Mat Kaplan] So, stand down Bruce Willis.

[Nancy Chabot] Haha, exactly.

[Mat Kaplan] Talk about why this is called the Double Asteroid Redirection Mission.

[Nancy Chabot] Yeah. So the target for the DART mission is the Didymos system, which is a binary asteroid. And that's really what enables this mission to be done in such a focused and cost-effective way. It's a binary asteroid which means there's a larger asteroid we call it Didymos A. it's 780 meters in diameter. And then there's Didymos B. It's a little Moon that goes around it and it's about 160 meters in diameter. DART is going to impact Didymos B, the little moon — sometimes referred to as Diddy Moon. Informally — not the official name. So DART is going to impact — the spacecraft is going to impact Diddy Moon at 6 kilometers per second. That's about 13,000 [00:10:00] miles per hour.

[Mat Kaplan] Not bad.

[Nancy Chabot] Yeah, so pretty fast. And what it's going to do is it's going to change the orbit of the moon around the main asteroid ever slow slightly. And the reason that this is really enabling for the mission is not the Didymos is going to hit the earth. It's not going to it's not going to hit the Earth and we're not concerned about that. But the spacecraft is going to be completely destroyed during this very high speed impact. We're going to be able to use telescopes that are on the Earth in order to see how the moon changes going around the main asteroid. And that's really what makes this mission such a great way to try to do this technology is because that's a way easier measurement then having to change its path around the sun which is what you would really be doing. So it's a great way to test this and it's also a safe target. You're just sort of hitting this moon slightly changing how it's going around the main asteroid.

[Mat Kaplan] There's been a lot of talk about not having contact on asteroid to redirect it but gravity tractors. We've seen artists concepts of these big spacecraft that sort of hover nearby [00:11:00] and just because all mass has gravity, they redirect. But this seems like a much more clever way to do it. If you're lucky enough to have an asteroid that has a companion that you might be able to get to in time.

[Nancy Chabot] Well, like you are saying this is the first time that this technology is being demonstrated at all. And and really there's a lot we need to learn about these different possibilities of how to redirect an asteroid how to nudge it slightly. A gravity tractor is something else that should be investigated. It could make a lot of sense in a lot of cases. Seeing how effective DART is is one of the main reasons of seeing how this if this kinetic impactor is it's called — basically ramming something into an object and budget slightly — how effective is that is that? Is a gravity tractor more effective in some situations? Are there other options that you'd want to use? I mean, I think it's way too early to start to rule out which mitigation technique or which way to nudge the asteroid is the most effective. We need to take a lot of steps and this is the first one.

[Mat Kaplan] Yeah, we're new at this. So clearly you want to see if it [00:12:00] deflects Diddy Moon, but won't Diddy Moon also possibly in a sense deflect the larger asteroid that that it orbits?

[Nancy Chabot] We have a lot of people modeling the dynamics of the system in order to really understand that. And we think we have a good handle that it's not going to have very much of an effect on that sort of thing. But we also are doing models where maybe it does. Maybe it causes landslides on the main asteroid and maybe that changes its period. From the Earth-based telescopes, we will be able to get how Diddy Moon is going around Diddy Main, if you will, haha, lots of cute little things. So how Diddy Moon is going around the main asteroid. But we’ll also be able to get the rotation rate of the main one. So we'll be able to see if it changes in some ways too. And with those two together, that'll kind of dynamic constrain the system and give us a lot of inputs.

[Mat Kaplan] They sound like cute anime characters, Diddy Moon and Diddy Main. Originally, this was going to be even more of a mission than is currently thought, because wasn't there going to be a second spacecraft in the original [00:13:00] concept?

[Nancy Chabot] So European Space Agency is very interested in planetary defense as well as is international. I mean planetary defense efforts are international efforts and they have to be by the very nature of it. We live here on the Earth together and this is for all of humanity. And so we collaborate very heavily. We welcome International participation and ESA was looking at doing a spacecraft called AIM to that was going to be there at the same time as DART and sort of really directly observe the impact event. That wasn't able to happen, but now they're looking at a new spacecraft called Hera which would actually get there a few years later and be able to image the impact crater and image the result of the DART impact and really still tell us a lot more about the system and let us see how the effects of the impact were. So DART is a standalone mission and we’re able to use the Earth-based telescopes, but sending a spacecraft to see really see that effect up is highly valuable and we really hope that ESA mission happens.

[Mat Kaplan] Was that a big part of choosing this particular space rock — that it would be visible [00:14:00] from Earth-based telescopes — so that we could see whether we'd have the desired effect?

[Nancy Chabot] Yeah. I mean, that's really why Didymos is a perfect system for this because you don't just need to have a binary, you need to have what's called sort of an eclipsing binary. One where the moon passes in front of the main asteroid. And so you can see this difference with its light curve from the Earth-based telescopes. And Didymos is perfect to be able to do that. And actually the timing for the DART impact is when the Didymos system is closest to the Earth. So the telescopes can really make the most precise measurement possible. So that's in October of 2022.

[Mat Kaplan] That's great. Lay it out for us. What is the status of the mission? And when is launch expected?

[Nancy Chabot] The launch window opens in June of 2021 — not far off! And so we're really in the throes of developing this mission. The engineers and the and the investigation team are working hard to make it all come together. We've got a major review coming up in June of 2019 and then impact in October of 2022.

[Mat Kaplan] You said this is under planetary defense, which is [00:15:00] interesting. It's not as much of a science mission as some, but certainly there is good science behind this.

[Nancy Chabot] There's definitely good science behind this but we really are focused on meeting the planetary defense investigation. My role on the mission is the Coordination Lead. Which is kind of the planetary defense equivalent of a project scientist on a science-driven mission. And it's not that we won't do science on this. It's just that the main things that are keeping us focused for this mission are meeting those planetary defense investigations. And there's a lot of overlap between science questions and planetary defense investigations, but they're also slightly different.

One of the things we want to do for the planetary defense investigation is understand where we impacted. That has a huge effect on how effective this is. So we want to see what the geology is like, see what the surface is, pinpoint that impact location. We want to understand the deflection. You have to understand the mass of the moon. And we need to understand the shape of the moon, and we need to understand where we hit with regard to the center of figure of that object to understand how the momentum is transferred [00:16:00]. And and these things translate to understanding the binary asteroids system as well.

So understanding the binary asteroids is interesting, but if this was a science driven mission, you probably would have a lot of questions about — how do binary asteroids form? How do these how are these systems different? How similar is the main and the moon asteroids to each other? Those aren't the questions that are driving us here. Instead, it's very much: we want to understand these objects because we want to be able to defend the Earth in the future.

[Mat Kaplan] Sounds like if, all goes well, we're going to add enormously to our knowledge in this area.

[Nancy Chabot] Yeah, there's nothing like going to these new worlds in person and really seeing what happens. We have good models. We think we understand how this momentum is going to be transferred when you impact the spacecraft into this moon, but we've been surprised by things in the solar system before. So, what we know about asteroids is that there is diversity and that they're also not just big slots of rock out there a lot of them seem to be rubble piles. Some of them have regolith. Some of them have [00:17:00] more boulders than others. Some of them are smoother than others. You know, how does that affect this impact event in the ejecta that's produced? Because the ejecta actually can enhance the momentum. So it's not just that we're running a spacecraft into it and edging it slightly, but the ejecta that shoots out is kind of like a jet which also helps with the amount of change that's induced on the system. So, how does that all work? How well are our models? I mean we have models they're based a lot of times and really small experiments that are done here on Earth in you know, gun chambers and the and that sort of thing, and they're done it centimeter scales. How does that translate to this real-life world scale that you would actually use to defend the Earth?

[Mat Kaplan] I was reading about the spacecraft itself. A lot of interesting stuff going on here. I mean, the camera that it's going to carry — such a critical component because, as you said, you need to determine very precisely where this impact is going to take place for us to really get the science that you're looking for. I read that this camera [00:18:00] is based on the one that we're hoping in a few hours is going to show us a much better image of Ultima Thule.

[Nancy Chabot] Yeah, so it's based off the same camera that's on New Horizons. So using that Heritage that camera has worked so spectacularly. And it's a long-range telescope so you can see something from far away and that also helps in this case. What's interesting about the camera on DART is that it's going to characterize the asteroid and characterize the target. And that is a very important part of what it does. But it's also doing onboard navigation. Because we want to hit the moon rather than the main asteroid, and you can't actually make that moon out where it is — separate it from the main asteroid — until about an hour before you impact.

[Mat Kaplan] Wow.

[Nancy Chabot] Yeah, so you have to do all of that onboard. So the spacecraft has to take these images that it's taking with the New Horizons heritage camera. And, onboard, sort of do this centroiding where it like figures out the difference between the main [00:19:00] asteroid and the secondary asteroid and then targets impacting into the moon.

[Mat Kaplan] And you clearly can't store that data the way New Horizons has, where we've heard that the data from Ultimate Thule is going to be coming back for the next two years. You don't have that luxury.

[Nancy Chabot] Well, but we do have the luxury of being really close to Earth. So what's awesome is that being so close to Earth, the downlink is amazing. It's nothing like being in the outer solar system. So during the week and definitely during the last day of the impact event for DART, we're going to have continuous DSN coverage. And so we're going to be able to send down one full frame image every 4 seconds. And if we subframe that, we'll be able to send down one image every second and that's the current baseline plan is that we'll be sending down an image in real time every second.

[Mat Kaplan] There's one more technical innovation on this. And I don't know how well you are prepared to talk about it, but it's ROSA. You know what I'm talking about here?

[Nancy Chabot] Yeah, the solar arrays. So [00:20:00] they've been used to demonstrate on the space station. And yeah, and they're going to be be great have here. It's not the only technology that's on this mission though. I mean, the next C engine is a main part of the DART mission.

[Mat Kaplan] The electric — or— Ion engine — or electric propulsion?

[Nancy habot] That's right. So it's going to be NASA's first flight of the of the C Ion propulsion engine. And that one's going to be hopefully used on other spacecraft going forward in the future. And so it's also another technology that NASA's demonstrating sort of fees into DAERT being a technology demonstration mission, if you will, demonstrating the next C technology and demonstrating planetary defense technology.

[Mat Kaplan] Is that an advancement? Let's say over the engines that got Dawn to Vesta and Ceres?

[Nancy habot] It is. it is definitely a new advancement and will be really enabling for future missions and we're excited to have it on on DART.

[Mat Kaplan] So does this mean that when the time comes from for that impact, there's going to be another gathering here at APL and lots of people like me — I hope including me — who are going to be [00:21:00] tracking this along with all of you?

[Nancy Chabot] Yeah, that's the plan! And especially for planetary defense, I think being open inclusive transparent about everything that's going on is just critical to the whole success of the larger mission that is the planetary defense, and that's been in every strategy document that's been released as well. Planetary defense is an International effort and that's it crucial part. And so absolutely we’ll be sharing all of the DART images as they come down, one per second.

[Mat Kaplan] Yeah, that'll be exciting.

I'm glad we've covered DART but your work doesn't end there. There is this other mission called MMX: Mars Moons eXploration — the X, the second letter in Exploration. It's not a NASA mission really, but I guess NASA and the US were contributing. Oh, yeah, it’s a JAXA mission. So the Japanese space agency is doing MMX and it's going to be the first dedicated mission to the Martian moons when it [00:22:00] successfully works and gets there. So it's going to go to Phobos and Deimos.

[Mat Kaplan] Both?!

[Nancy Chabot] It's going to reconnaissance with both of them. But the main focus of MMX is to return a sample from Phobos. So, it's not just going to go there and characterize these moons. But it's going to go down to the surface of Phobos and get a sample and bring it back to Earth.

[Mat Kaplan] We all know that sample return is pretty much the hardest thing that you can do out there with robotic spacecraft. We know too well at the Planetary Society because of the Russian Mission Fobos-Grunt, which of course never made it even out of the Earth's atmosphere. But a lot of science to do along the way, just as OSIRIS-Rex is doing right now. We're still like a year away from it picking up its sample at asteroid Bennu. We've heard this before but, getting it from you: why is it so important to get these pristine samples back from these small bodies?

[Nancy Chabot] I could go on and on about that. So I got my graduate work working on [00:23:00] meteorites and that was like a lot of my background. And so I really appreciate how much you can do here in the Earth-based labs. That’s going to always far outperform capabilities that you could put on a spacecraft. And not only that, it's sort of like your whole payload is here on Earth and it advances. And we're still studying Apollo samples even today. Decades later, as you get new instruments, you can go back to those samples. You can remake these measurements. You can do new measurements you didn't even know we're possible. In meteorites, we’re constantly finding new things as techniques get better and better and smaller and smaller and pre-solar grains and age dating, different components in them and… So there's really no comparison to the measurements that you can make when you have to have a very limited payload on one spacecraft that's built at one time and goes there. Versus bringing something back and having it not just for the current generation, but all future generations of scientists going forward.

So sample return is crucially important. And what distinguishes it [00:24:00] from meteorites is — meteorites are a little biased. They are the ones that have survived passing through the Earth's atmosphere and Fallen onto the planet, that we've gone and picked up. It doesn't look like they've been that heated in the interior, but weak stuff probably didn't survive. It truly didn't survive the passage through the atmosphere. It's burnt up. How do these samples that haven't gone through that process, when you really want to understand it, compare? That's the main thing, is that you're going directly to the source. It's not contaminated by the Earth's atmosphere. It's not contaminated by sitting around on the Earth. It's directly what these objects are made out of.

[Mat Kaplan] Do you subscribe to this hypothesis that the moons of Mars may be captured asteroids?

[Nancy Chabot] Well, what's interesting — and I think what's exciting about the MMX Mission, the Martian Moon eXploration Mission — it's so set up to answer that question. In some ways, you look at the Martian moons and they look a lot like asteroids. They’re irregularly shaped, their spectral characteristics are very much like asteroids. That said, they have [00:25:00] really weird orbits. So they're both in the same plane, one spiraling inward once spiraling outwards from Mars. Were they captured at the same time then, but in these really different orbits and in the same plane? That seems unlikely and Mars is not that big. So Mars capturing stuff is kind of dynamically difficult. When people try to do those models, they need to have a much thicker atmosphere for Mars that drags these things down and slows them down and puts them into the orbit. So dynamically, It's been very difficult to explain them as captured asteroids. Even if they look like captured asteroid, but they do look like captured asteroids! They share a lot of characteristics in some ways.

On the converse then, one of the more recent theories has been that there was a giant impact on Mars and the Martian moons are sort of those objects — the last objects that remain that reaccreted and made the moons.

[Mat Kaplan] Much as we got our moon.

[Nancy Chabot] Much as we got our moon! But it looks very different than our moon doesn't it? Right? And there's two little irregularly shaped, you know, lumpy objects going around Mars there. Is that like how our moon formed or not? Because they don't look the same [00:26:00] anymore. And when you look at the moons, structurally they don't look like they're made out of Martian crust material. Of course, if you had a giant impact, it would be a mix of Martian crustal on material and the impactor material and -- how would that play out? And what would this dusty gas disc do when made these moons? There's a lot of really interesting questions. What's great about this one though is — this is how science is done, right? You put a hypothesis out there — two hypotheses out there in the literature. They've been published, you know, and they make predictions for what the composition should be. And the two predictions are very different. And so let's go and make that compositional measurement and we'll be able to tell!

[Mat Kaplan] Science at its best.

[Nancy Chabot] Yeah.

[Mat Kaplan] Tell us about the instrument on MMX that you serve as the Deputy PI for.

[Nancy Chabot] Yeah, so MEGANE is the Mars Moon Exploration with Gamma rays and Neutrons and this is a Japanese JAXA mission, but this is a NASA instrument. So NASA is partnering with with JAXA in order to deliver this instrument [00:27:00] on this mission. And it's a gamma ray and neutron spectrometer. And MEGANE actually means “eyeglasses” in Japanese. Along with being an acronym. And we like to say that what this instrument is going to do is it's going to enable the spacecraft to see with this new pair of glasses the composition of the surface. Because that's what gamma rays and neutrons allow you to do.

[Mat Kaplan] I was curious when I read about the instrument a few days ago. I thought, wait a minute, neutrons are particles, gamma rays are photons — very energetic photons. How do you measure both of those with one instrument?

[Nancy Chabot] Well, it's got multiple sensors, multiple detectors. So that's sort of the short thing. But they're very complimentary. It's sort of by getting the neutrons and the gamma rays together, you can get a better picture of interpreting both of those data sets.

[Mat Kaplan] How will looking for these energetic neutrons, gamma rays, how will that help us to understand what these moons are made of?

[Nancy Chabot] Galactic cosmic rays, when they hit the surface of the moons — or just elements that [00:28:00] naturally radioactive decay — they give off characteristic gamma rays and neutrons. So different elements release a different gamma rays than other ones. And so by measuring them you basically can take that gamma ray spectra and figure out what the elemental composition is. So. It's kind of a direct measurement of — what are the rocks made out of on the surface of these moons?

[Mat Kaplan] This instrument, does it also have some heritage from from other missions? And and I also read that it has there's a future mission even beyond MMX that this going to carry something like this?

[Nancy Chabot] The gamma ray portion is heritage from Messenger — highly successful mission, the first one to orbit the planet Mercury. The neutron spectrometer is Lunar Prospector heritage. This instrument is a very similar one that’s going to go on the Psyche mission.

[Mat Kaplan] Psyche, which is — we heard a little bit about here yesterday from that Pi, that Principal Investigator — going to this really strange metal asteroid, which we have not visited yet, right?

[Nancy Chabot] We have not! I'm very [00:29:00] excited about that and it should be a very different type of object than the other asteroids that we've been to. What's it going to look like? I don't know, but it'll be great to have a gamma ray and neutron spectrometer to get the composition of what it's made out of.

[Mat Kaplan] Asteroids, comets, collectively known as “small bodies” — I guess that includes the moons as well, maybe even ring particles, right? Which are, what, tiny moons. You are pretty fascinated by these little guys.

[Nancy Chabot] When we group all these things as small bodies, it's kind of interesting to me because in some ways it doesn't necessarily make sense to group all of these objects together. What? Just because they're not planets? I mean, some of them are even moons, right? I mean and why would the outer solar system — because you have an object way out there — why would you compare that to an asteroid like Psyche, which is maybe a stripped metallic core? I mean the questions that you ask with these worlds are so different. And so, in some ways they've been all lumped together under this [00:30:00] category of small bodies if you will, but it's almost like a little lazy. Because it covers such a diversity of objects that you study for very different reasons. We were just talking about planetary defense, right? You know, I mean and planetary defense is a really important thing to do and it has its own sort of strategy and its own priorities, right? New Horizons going out there seeing what's out there in the outer solar system. That has very important reasons to do it too — to understand our own solar system and what really is out there on the fringes, right? There's not necessarily a ton of overlap between those those priorities and they're both equally important. But then to just lump it all together and be like all small bodies or small bodies is it's kind of weird in some ways.

[Mat Kaplan] And they're so diverse. I mean, wonderfully diverse!

[Nancy Chabot] Yes, exactly! They're wonderfully diverse. So why are we like lumping rather than splitting? You know, why do they get all put together in the same sort of category? I think some of that is historical. Is that people looked at planets first because you know planets are planets and they’re big and you study them, and [00:31:00] then — everything that wasn't planned — it kind of got lumped together, but it might be time now that we're learning more about the diversity of all of these different worlds out there to stop lumping so much and start to appreciate the differences.

[Mat Kaplan] Lumping — I was going to say ‘no pun intended?’ I mean, there are people who are ring specialists, right? Moon specialists, asteroids, comets. Nevertheless, they have been lumped together. And in fact as far as NASA is concerned American Science. There's this group called SBAG, which you were the leader of for several years.

[Nancy Chabot] Yes, so I was was the chair of SBAG, which is the Small Bodies Assessment Group from 2013 to 2016. I was on the committee before that and then I was past chair through 2017.

So I was a lot of time working on on that group and that committee, and it's basically the way for the community to come together and talk about the priorities in the exploration of the small bodies in our solar system. And again, there's a whole range of [00:32:00] priorities and that's really what makes these meetings so interesting. And you can't really weigh one necessarily against each other. I mean, you don't really want to be in the case of saying — you know, which one is more important? Is it more important to be going to the Martian moons for the first time or exploring the Kuiper Belt for the first time? Those are really different reasons to do that. They tell you very different things. I mean Psyche is going to go to potentially a metallic world, right? We think. And Lucy is going to figure out what the Jupiter Trojans look like for the first time. We're still really just trying to understand what is in our solar system. And a lot of the small bodies missions are the first discovery — first exploration. When they're not, sometimes it's because these objects are accessible. Sample return, like we are talking about, immensely valuable. It's easier to bring a sample back from an asteroid than from Mars. That doesn't mean Mars sample return isn't a very high scientific priority. It just means that we can do a mission like OSIRIS-Rex right now, where we can't do Mars sample return on the same sort of budget and the same sort of technology. Sometimes [00:33:00] it's a matter of being close and accessible and sometimes it's a matter of going there for the first time and seeing what these things look like. And so there's there's a huge diversity in the small bodies community and that's great. It makes it for a really compelling exploration of the solar system and a lot of interesting discussions at those meetings.

[Mat Kaplan] You know, I had not thought of this. And I should have because the evidence is always been right in front of me as I talk to people like you — your colleagues who do have these specialties that are lumped together, as small bodies. That it parallels the the people who study Mars and are very happy that so much money has gone into researching Mars. But then you have the people who want to do more with Venus or with the ice giants that, of course, Uranus and Neptune of only been visited once, ever!

[Nancy Chabot] And briefly, very briefly! And imagine I mean, so many interesting moons are going to be around those objects that we have yet to even discover. I mean just even [00:34:00] going back to the small bodies angle. Because that kind of winds up those discussions a lot of times happen — the irregularly shaped moons, which are the majority of the moons around these outer planets.

[Mat Kaplan] So regardless of the fact that we can't do everything at once, we wish we could...

[Nancy Chabot] I wish we could! There is like no shortage of things to explore in the solar system.

[Mat Kaplan] And we will keep pushing to make it possible to explore as many as possible at the Planetary Society. Nevertheless, would you agree this is a pretty good time — not just for planetary science — but for small body exploration?

[Nancy Chabot] I think that there has been an appreciation that there's a huge diversity of small bodies out there and that's really what's enable so many missions to be going out to seeing what these things look like for the first time. As the data have come back and showed that these small worlds are not all the same. They can be vastly different from each other. It's made us more compelled to go out and check out these other, you know, small worlds that are out there and see what they look like as well.

[Mat Kaplan] How about you [00:35:00] personally? I think you said that this has really been a focus for you at least since your undergrad days. Why do you have such a fascination for these?

[Nancy Chabot] I think I have a fascination for the solar system and for space in general. I did a lot of astronomy as an undergrad and things like that, but something about solar system exploration that really grabbed me when I was deciding what to do for grad school, was that it's so accessible. It's it's not just looking through telescopes. Looking through telescopes is awesome and tells us so many things about the universe in general. But I really gravitated to being able to hold a sample in your hand in the lab, right? And being able to send a spacecraft out there and land on that body, you know, and now land on that body and bring a sample back. Its space but it's our space. It's our closest space, and we are on a planet! We are on the Earth. How do these other planets compare to the earth? It's that sort of accessible space that that really kind of drove me. And a lot of stuff I've done has been on small bodies, but I think [00:36:00] the whole solar system is fascinating. I think that we should go explore all of these places that we haven't been. And I think any of these discussions where we try to you know, pit one against the other — there's no reason for that. At the end of the day, it's all part of our solar system. And any time we learn one thing about one object in there, it tells us more about the whole. So we need to go everywhere and to understand it.

[Mat Kaplan] Well put. I want to make sure that we mention here that you have gone literally to the ends of this Earth to …

[Nancy Chabot] One of the ends!

[Mat Kaplan] One of the ends! Right, the bottom end. Right, the bottom end. Unless you're in Australia. They may think of it as the top. But, you've been to Antarctica.

[Nancy Chabot] Yeah. I was fortunate enough in grad school to go with the Antarctic Search for Meteorites program for the first time in order to collect meteorites down there. That's a NASA and NSF funded program that sends us scientists every year to collect meteorites. And then the meteorites come back and they go to NASA Johnson Space Center and they're curated there. And then they're made available to the entire [00:37:00] international scientific community. In a given field season, we’ll collect somewhere between 200 and 1,000 meteorites.

[Mat Kaplan] Wow! That's more than I expected.

[Nancy Chabot] It's a lot and so this has been going on for a while. So there's over 30,000 meteorites that have been returned this way. And so it really is this great resource. And when they set it up, it was very forward-thinking in order to not hoard these samples but to then put them up as available to the whole international community. Because it's more than any one person could study. In fact, it takes the whole science community to try to understand what's out there. And it's still going on. So I went once as a grad student and then I had a postdoc where I went for 4 more years. So I've been 5 times total.

[Mat Kaplan] Wow. Okay, that's one more reason for me to envy you. And there is another reason that I envy you and a number of people who've been on this show. What does the number 6899 mean to you?

[Nancy Chabot] Haha, yeah, I have an asteroid named after me so — which is amazing. Sometimes I do just like [00:38:00] Google it on the JPL page so I can watch myself go around the Sun. There are really things about being in this field and planetary science that never get old. Seeing those images of a new world for the first time. And I'm just so fortunate to be a part of this exploration.

[Mat Kaplan] Thank you Nancy. This has been delightful.

[Nancy Chabot] Thanks for having me.

[Mat Kaplan] Time for What’s Up? on Planetary Radio. Bruce Betts is the Chief Scientist for the Planetary Society. Does a lot of other stuff for us. He's here to do one of those things and that's to tell us about the night sky and play along as we check out What's up?

[Bruce Betts] What's up? Hey, Mat.

[Mat Kaplan] Hey there!

[Bruce Betts] So in the pre-dawn sky, we've still got a planet party with bright Jupiter in the East in the pre-dawn, looking bright. And then below it to its lower left is super bright Venus. And then below that is yellowish Saturn, much dimmer. But on February 18th, Saturn will be hanging out near Venus [00:39:00] and then after that Saturn will be higher than Venus. So much going on. We also have reddish Mars in the evening Southwest getting lower and dimmer. And hey, check out Orion if you haven't, because it's doing it's beautiful winter thing in the South/Southeast in the early evening. And there are all sorts of bright stars in that region of the sky. So have fun.

[Mat Kaplan] I did point out Orion to my two and a half year old grandson. He didn't care. I'm hoping that that that enthusiasm grows a bit as he gets older.

[Bruce Betts] I assume he's an avid reader, so, you know, you should give him Astronomy For Kids.

[Mat Kaplan] Haha, no, mostly he likes Broadway tunes.

[Bruce Betts] Well, then he's going to love my Broadway space musical.

[Mat Kaplan] Haha, I can't wait!

[Bruce Betts] Yeah, neither can I.

Onto this week in space history: 1971. That's right, Alan Shepard hits golf balls on the moon. Great moments in space history. And then [00:40:00] 1974, the last crew left Skylab. Last crew to be on board Skylab.

We move on to... Raaaandom Spaaaace Faaaaaact, oh yeaaaah!

[Mat Kaplan] Last time I heard somebody talking like that, I think I was at the county fair.

[Bruce Betts] Step right up! We happen to be recording this on Chinese New Year. The Chinese calendar is astronomically based but, kind of complicated. It's lunisolar. So its based on moon phases but also tied to the solar year. They're usually 12 months. By this meeting, the lunar cycle of phases — so about 29 and a half days — usually 12 months to a year. But then to make everything work, you have to, every few years have a leap month, so there will be 13 months per year. I guess this is why people usually just look up when the New Year [00:41:00] date is. But this is why it shifts around so much, because sometimes you got a whole leap month hanging out in there.

[Mat Kaplan] Thank you. I had no idea that there was something — some scheme that combine both lunar and solar calendars. That's — that's crazy.

[Mat Kaplan] Yeah, there's a lot more detail, but we don't have time for that right now.

[Mat Kaplan] Nah.

[Bruce Betts] Because we have to move on to the trivia contest where we have lots and lots of winners! I asked you: what was the last human mission to end with a splashdown in the Atlantic Ocean? How'd we do, Mat?

[Mat Kaplan] This is unprecedented. Not only did we get a big crowd of entrants, but we have never had such a crowd of prizes to give away to people who got it right and were picked by! Shall we just give the answer first? Go ahead!

[Bruce Betts] Apollo 9 on March 13th, 1969 was the last — with people on board — to splash down in the Atlantic Ocean.

[Mat Kaplan] Yeah, I had a few people who got a little bit off-track [00:42:00] here, but almost everybody got it. As I said, among the people who got it right, here are the five winners of that Blu-ray copy of First Man — the movie about Neil Armstrong and his accomplishment. He splashed down too, but in the Pacific.

Anthony Doreso in West Haven Connecticut, Charlotte Marshall is London the UK, Carter Kindley in Eugene, Oregon, Ken Adams in Dunlap, Illinois, and Michael Suresco in Adrian, Michigan. Well, wait, there's more! We also have — yeah, you met Dante lauretta, of course of the OSIRIS-Rex mission — he has those great board games that he makes. He offered us a couple and we're going to the game known as Extronaut, his first effort. That's going to go to Seth Mason in Newmarket, New Hampshire. A newer one, Constellations, is going to Denusha Mahipula [00:43:00] in Tucson, Arizona. And there's even more! Keith White in Ottawa Ontario: he is going to get that set of five kick asteroid stickers and 200 point account. Wow.

[Bruce Betts] Wow. You are so generous, Mat.

[Mat Kaplan] I try. Got a little help from a whole bunch of people with this one. Charlotte Marshall — she was one of the winners that you just heard and Brian Hewlett and a whole bunch of other people came up with this — that the last human mission ever to end with a splashdown was the Soviet Soyuz 23, which was an accident. Did you know about this? It began to sink into a frozen lake after landing in the middle of a blizzard!

[Bruce Betts] Yeah, pretty scary. I wouldn't have thought of defining that as a splashdown. But yeah, I suppose. Unintentional.

[Mat Kaplan] Haha! Andrew Zimmerman in Tokyo — this is nice, “The recent Planetary Radio episode about Apollo 8 really brought home the incredibly [00:44:00] brief time frame that played out between the first human Apollo Mission, Apollo 7 in October 1968, and Apollo 11, July 1969 — five missions in 10 months. Wow!” Says Andrew.

Dave Fairchild, our poet laureate:

Apollo 9 returned from space and splash down in the ocean

Back in 1969 is when I have the notion

Somewhere near the islands that we know is the Bahamas

Still clad in their space suits that had doubled as pajamas.

Finally, Robert klain in Chandler, Arizona. And he obviously is aware of the astronauts who crewed Apollo 9. He says, “Mat and Bruce, given that Valentine's Day is coming up fast, would you be my Schweicarts?” It's a bit of a stretch but I like it.

Alright, we got through it! We're ready for another one.

[Bruce Betts] All right, everyone. How long [00:45:00] was the longest Skylab mission — the US space station in the early 1970s — How long was the longest Skylab mission? Meaning, how long was the longest that humans were on board in one continuous stretch? Go to

[Mat Kaplan] We are going to give you this time until the 13th. That would be Wednesday, February 13th at 8:00 a.m. Pacific time to get your answer in. And somebody — just one person is going to get a 200 point account from that great worldwide network of telescopes. They're also going to get the set — the full set of five kick asteroid stickers from — the ones that Bruce Betts helped to develop. And one more thing: the Universe Today Ultimate Guide to Viewing the Cosmos: Everything You need to know to Become an Amateur Astronomer. Beautifully done book by David Dickinson, written [00:46:00] with Fraser Cain the publisher of Universe Today. Of course, he and Pamela Gay are the hosts of Astronomy Cast, that other great space podcast that probably a number of you listen to, and Pamela wrote the foreword for this. It's beautifully Illustrated. It's almost a textbook but really pretty. If you're a grown-up, this is a good way to get into astronomy, I would say. But if you're a kid — gosh, if only there was another book that was good for kids to get into astronomy. Even if they don't have a telescope. How about Astronomy for Kids?

Okay enough of that. We're done.

[Bruce Betts] All right, everybody go out there, look up the night sky, and think about where in the world you would like to splash down. Thank you and good night.

[Mat Kaplan ]And that is Bruce Betts the chief scientist for the Planetary Society who joins us every week here for What's Up?

Planetary Radio is produced by the Planetary Society in Pasadena, California and is made possible by its impactful members. MaryLiz Bender is our Associate [00:47:00] Producer. Josh Doyle composed our theme, which was arranged and performed by Peter Schlosser. I'm Mat Kaplan. Ad Astra.