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Season 5, Episode 18: How to Move an Asteroid, with Nancy Chabot

Season 5Episode 18Nov 19, 2021

NASA’s Double Asteroid Redirection Test Mission, or DART, will deliberately impact a small asteroid called Dimorphos to deflect its orbit around a bigger object, Didymos. Nancy Chabot, planetary scientist at the Johns Hopkins University Applied Physics Laboratory, has the details.

Gravity Assist: Season 5 Trailer – What’s Your Gravity Assist?

Planetary scientist Nancy Chabot has been to Antarctica five times to look for meteorites.

A spacecraft is about to begin its journey to crash into an asteroid on purpose. NASA’s Double Asteroid Redirection Test Mission, or DART, will deliberately impact a small asteroid called Dimorphos to deflect its orbit around a bigger object, Didymos. While this system presents no danger to Earth, an asteroid the size of Dimorphos would cause regional devastation if it hit our planet. DART will demonstrate a potential method of protecting Earth from hazards in the future. Nancy Chabot, planetary scientist at the Johns Hopkins University Applied Physics Laboratory, has the details. She also discusses searching for meteorites in Antarctica and discovering the secrets of planet Mercury.

Jim Green:NASA has a mission called DART that will help us understand how to defend the planet against incoming Near-Earth Objects.

Nancy Chabot:It’s purposely going to crash a spacecraft into an asteroid to move it a little bit. And this is the sort of thing that you might want to do if there was an asteroid in the future that was headed towards the Earth and you wanted to move it a little bit so it wouldn’t hit the Earth.

Jim Green:Hi, I’m Jim Green. And this is Gravity Assist. We’re going to explore the inside workings of NASA in making these fabulous missions happen.

Jim Green:I’m here with Dr. Nancy Chabot. And she is the planetary chief scientist at the Johns Hopkins University Applied Physics Laboratory. Nancy, you also have an asteroid named after you, asteroid 6899 Nancy Chabot. Nancy, welcome to Gravity Assist.

Nancy Chabot:Thanks. I’m so happy to be here.

Jim Green:Well, you have been so active in researching what we typically call small bodies of the solar system, such as meteorites on up to even bigger small bodies. That material really comes together and over time builds up planets and larger objects. How did you get involved in that field?

Nancy Chabot:I actually didn’t even knew this field existed until I went to grad school. I was an undergrad in physics, because I wanted to go into space science. And I thought, rhis is what you needed to do to go to into astronomy actually didn’t even realize that, like planetary science was a thing that you could do with your life. And then even when I went to planetary science school, I sort of thought more about like missions and that kind of stuff. And it wasn’t until, you know, somebody introduced me to meteorites, and then all of a sudden, it was like, wow, these aren’t just things that we can look at, we can actually hold them in our hands. So rocks from space that you can actually hold in your hand and bring into the lab and inspect on a fine scale that you can’t possibly do otherwise. So, I think that just really was an aha moment for me that it’s like you could study space, but you can do it here and get your hands on it too.

Jim Green: Well, where do meteorites come from? And why are they so interesting?

Nancy Chabot:Well, mostly, meteorites come from asteroids, which is fascinating in itself. Though I’ll just say, you know, quickly that we do have a few from the Moon. And there are only samples from Mars currently, that we have that, here on the Earth. And so that makes them really valuable. But my research has been mostly with the asteroids. And, you know, I think the thing is that sometimes people are really surprised to learn that, you know, meteorites are all different, just like Earth rocks are all different, right?

Nancy Chabot:I mean, there’s really no reason that you would think everything out there in space would sort of be the same. People have this one vision a lot of times have this is what a meteorite is and it’s like, no, no, no meteorites are sampling this huge diversity of different bodies. I mean, some of them are, you know, 4.5 billion years old, they predate the planets. They’re like the garbage bag and leftovers that didn’t form the planets, but they let you look back into the first solids that solidified in the solar system, what was going on in our solar system before there were planets. And then some of them made, like, mini-planets, planetesimals, right, where they melted, and they made these metallic cores and these rocky mantles and had volcanic processes on the surface. And we have samples of those too, and they all look different. But similar to some of the Earth’s rocks to it just shows you the you know, the Earth is just part of our solar system. So it really ties it all together.

Jim Green:Meteorites that are different. Does that mean they’re generated or put together in different places of our solar system?

Nancy Chabot and Andy Rivkin, researchers at Johns Hopkins University Applied Physics Laboratory, are pictured with the DART spacecraft.

Nancy Chabot: Yeah, maybe. We think that some of the stuff we’re learning from meteorites right now, some of the cutting-edge research has to do with these isotope systems, which is a really detailed measurement, again, showing you the power of meteorites and using Earth-based analysis to do this. And now we have samples from both of these populations of the inner solar system and the outer solar system potentially. And that’s one reason things can look different. But things can also just look different depending on how big the planetesimal grew. So if things never grew very big, they didn’t melt. And so you can retain these primitive characteristics. But you know, if things grew to 10 kilometers, 100 kilometers, or larger, then that could have different processes that go on as well, just because the bodies are different sizes. But yeah, where they formed in the solar system can have different compositions. You know, this might be why Mercury looks different than Mars, for example. So meteorites help to put all of this into context.

Jim Green: Well, I heard that you’ve been to Antarctica five times. What was that like? And what were you doing there? Looking for meteorites?

Nancy Chabot:I was so fortunate to go the first time when I was in grad school with the Antarctic search for meteorites program, ANSMET. Yeah, which is a great program that joint with NSF and NASA and the Smithsonian. It’s been going on for decades, and is hugely successful at collecting meteorites. Antarctica is just an amazing place to go get meteorites, and I got to go the first time as a grad student.

Jim Green:Did you have an easy time or was it hard and cold?

Nancy Chabot:Antarctica pretty much is always cold. But it was an amazing experience. So, what we do for ANSMET, every season, is we get teams of between four to eight people. And then we get dropped off in the middle of nowhere on these blue ice fields, where you’re 100 miles away from the next people in the entire world. The Sun is up 24 hours a day when we go. And the landscape is really other-worldly in a lot of ways. Big horizons and ice, a lot of ice. There’s some mountains too. And it’s very different than your, my life and most other people’s lives on a daily basis. You’re chipping ice in order to get your water. You’re you know, getting to know your other campmates very, very well. (laughs) Because there’s nobody else around. It’s hard. I mean, for sure. But it’s, it’s amazing. And it’s a great opportunity that everybody who’s been able to go with ANSMET really appreciates and this, sort of this, moment in your life that you would never trade.

Jim Green:So you get in snowmobiles. And you, you start across the ice sheet. And and you see these black objects, and they’re meteorites. Any of particular interest to you?

Nancy Chabot: What’s amazing about Antarctica is you’d be down there for six weeks, and an average field season finds between 100 and over 1000 meteorites during that period of time, just in those few weeks. Depending on where you are, you could find 100 a day, sometimes. They’re just sitting there collected by these natural ice movements waiting, you know, sort of, for us to find them and then share them with the world so we can uncover all their secrets. I don’t know it’s hard to pick favorites among meteorites, I have my own personal ones, I personally worked on iron meteorites a lot. And pallasites are closely related, which are made of olivine and metal intermixed together.

Nancy Chabot:Pallasites are a type of meteorite that we think comes from the core mantle-boundary of an asteroid, because they have really beautiful olivine crystals in them, like gem quality.

Nancy Chabot:I remember one time we were on a pretty small field team, there was four of us. And we were driving around on our snowmobiles. And we found this giant pallasite. In fact, it was so heavy, I couldn’t pick it up. (laughs) We had to get like two people to put it onto their, onto this sled.

Nancy Chabot:And we’re like, wow, this is great. But then you know what? Then we found another one, another giant one! And then we found another giant one! And it turns out there was this whole strewn field of pallasites along this site. And it never got old. you might think, oh, after a few days, aren’t you tired of finding these giant pallasites from space? And it’s like, nope, nope, just keep bringing it on. I’ll take all of them that you would give me.

Jim Green:Well, you’ve also worked on NASA’s MESSENGER to the planet Mercury. How did you get involved in that mission? And what was the most exciting results that that you found in analyzing that data?

Nancy Chabot: Yeah, I feel like I’ve been really fortunate to have a lot of opportunities. I mean going to Antarctica, you know, five times was was one of those and then getting this job here at Johns Hopkins Applied Physics Lab allowed me to become involved with the MESSENGER mission. I actually started off on that mission helping run their website. So I was sort of updating the science content for the website. And one of the things related to that was putting out featured images from the camera. Well, then it turned out, “Hey, maybe you want to get involved with the camera team?” And I’m like, “Yeah, I want to get involved with the camera team. That sounds amazing.” You know, and, and then by the end of the mission, I was actually the lead scientist for, for the camera on MESSENGER and in charge of the geology discipline group. So leading a lot of the science that was going on.

Nancy Chabot:And I think one of the things that I love working in planetary science is that you always have to learn new stuff. And so you know, here, I came from this physics background. And then I was doing this geochemistry of meteorites and going to Antarctica. And then I had to learn all about spacecraft cameras and image analysis and looking at the planet. But it was really, I just relished and appreciate having had that opportunity.

Nancy Chabot:So you asked about some of the like, most exciting parts. Before MESSENGER, we only seen 45% of the planet. Like literally, here’s another planet in our solar system. And we don’t even know what it looks like, right?

Nancy Chabot:And so these images are just streaming back. And they’re parts of the planet that we’ve never seen before. We’re literally mapping the planet for the first time creating the first global view of what it looks like. And I just can’t. It was like a childhood dream come true to like, look at my computer each day and see these new views of something that we had never seen before. And I know I’m not the only one on the team that felt that way. And that was also, made it so rewarding to be on this team where we were doing this all together and so much data was coming in and really revealing this new world right before our eyes.

Jim Green:Well, you know, the next mission to Mercury is the ESA-JAXA BepiColombo mission. And I hear you’re involved in that too.

Nancy Chabot:I am.

Jim Green:How did that happen?

Nancy Chabot:So when I worked on MESSENGER, I started to specialize a lot on ice in the poles. So there’s these regions on Mercury that never get direct sunlight. It just doesn’t have much tilt. And so these craters are just always very, very cold. And there’s ice in them. MESSENGER made a lot of good discoveries in order to tell us about that. And, and that’s sort of what positioned me then to be able to join the BepiColombo team to take that to the next step with BepiColombo, and what is going to tell us about the ice at the poles of Mercury.

Jim Green:Well, you know, another fantastic mission that’s about to launch is called the Double Asteroid Redirection Test, or DART. What is DART going to do? And how does it do it?

Nancy Chabot:DART is an amazing mission. It’s launching very soon. And it is a planetary defense mission. And what it’s going to do is it’s purposely going to crash a spacecraft into an asteroid to move it a little bit. And this is the sort of thing that you might want to do if there was an asteroid in the future that was headed towards the Earth and you wanted to move it a little bit so it wouldn’t hit the Earth.

Jim Green:Wow, that sounds fantastic. Well, what asteroid are you gonna hit and deflect?

Nancy Chabot:So like the name says, it’s a double asteroid system, hence the double asteroid redirection test, and there’s two asteroids. There’s the larger Didymos, which is 780 meters in diameter and it has a small moon that’s named Dimorphos. and it goes around every 11 hours and 55 minutes, it’s 160 meters in diameter. So smaller, much smaller than Didymos. We know this because telescopes here on the Earth have been looking at these asteroids for decades. And they’ve mapped this out. They’ve discovered this double asteroid system. And so what DART is going to do is it’s going to target Dimorphos, the smaller of those two asteroids, and it is going to hit into Dimorphos.

Nancy Chabot:And it’s going to ever so slightly deflect how Dimorphos goes around Didymos. So moving the asteroid, just a tiny bit, about how it goes around the larger asteroid. And so it’s a small little nudge, this is what you would want to do for planetary defense. Planetary defense with a kinetic impactor technology like this is definitely about deflection not disruption. This is in no way looking to blow the asteroid up. It’s just going to give it a small nudge and make a small change in its period. And we think it might be about 10 minutes, so maybe 11 hours and 45 minutes will be what the telescopes measure after DART’s collision. But we don’t know for sure, and that’s one of the main goals for the DART mission is to make that measurement.

Jim Green:What kind of damage would an asteroid the size of the moon of Didymos cause if it hit the Earth?

Nancy Chabot:Yes, Dimorphos at 160 meters is one that we really are concerned about, if something the size of that hit the Earth. So sort of a kilometer and up are the size that you worry about for global extinction events. So dinosaur killers, if you will, and happy to say that we’ve found the majority of those asteroids, the large majority over 90%, none of those are on a collision course with the Earth. We’re tracking them. So global extinction events, and like the dinosaurs are not in our future. But these few hundred-meter size ones – we’ve only found less than half of the population actually. So we are still looking. And that’s an important part of planetary defense. planetary defense is not just about deflecting asteroids, it’s also finding all the asteroids, figuring out where they are characterizing them, keeping track of them. But then it’s also taking this first step to be ready in case you needed to. So something on the size of Dimorphos, if it was to hit the Earth, would be regional devastation, it would be hundreds of kilometers wiped out. And sort of, you know, devastating over large urban areas or something the size of a small state in the United States. So regional devastation. It would be catastrophic.

Jim Green:Is there a chance in the future that it will come around and hit the Earth?

Nancy Chabot:Yeah, there is no chance that Didymos and Dimorphos, or a danger or a threat to the Earth. They’re not on a collision course with the Earth in the future. That makes them really appropriate for this first test. You know, being the double asteroid system, that binary asteroid system really is enabling for the telescopes. But of course, if you’re going to do a first test of asteroid deflection, you want to do it on something that’s not a danger to the Earth as well.

Jim Green:Well, how fast is DART moving when it impacts Dimorphos?

Nancy Chabot:So DART comes speeding in really fast, 15,000 miles per hour. It needs to be going really fast, it needed to give this asteroid a small nudge, because the spacecraft itself, the main body of it without the solar arrays is about 100 times smaller than the asteroid that it’s trying to move. So you can see you have to come in pretty fast just to give it this small nudge.

Jim Green: Well, you know, that impact’s going to happen next year. Will the public have an opportunity to see it if they look up into the sky?

Nancy Chabot:The impact is happening late September, potentially, October 1st, we’ll know once we launch for sure what the impact date is. And this time of 2022 was specifically chosen, because the distance between Earth and Didymos is at a local minimum. So it’s actually not going to be this close to the Earth again for another 40 years. So that enables the telescopes here on the Earth to get the best data possible. But we’re still going to use some pretty big telescopes in order to be able to make that measurement.

Nancy Chabot:So just looking up, you won’t necessarily be able to see a bright flash and a lot of ejecta all over there. But, Hubble Space Telescope is going to give it a try. And James Webb Space Telescope, hopefully, will also be giving it a try to get whatever data they can. So, but we are going to be streaming the images back to Earth, one per second. And so we’ll be getting these smart-nav images sent back to Earth at the same time. And we’ll be seeing them one a second, one a second, it’s not going to look like much until you get really close. And then it’s going to be speeding in, show the surface of the asteroid, and then the images will stop. So people can look forward to seeing that at least.

Jim Green:Well, let’s hope they stop, because that means you’ve impacted Dimorphos.

Nancy Chabot:(laughs) Yeah, that’s, it’s, that last image is going to be pretty spectacular for sure.

Jim Green:So Nancy, after the impact of DART on the moon of Didymos, what happens next?

Nancy Chabot: Well, what happens next is there’s an Italian CubeSat called LICIACube. And it actually makes a close flyby three minutes after DART’s collision. And it captures some spectacular images of the ejecta and the collision event itself. And but it’s actually going to take it a few weeks to send all those images back to Earth. So those images will be streaming back. And we’ll be looking forward to them to see the ejecta pattern. But then the telescope here on Earth also get to work because they have to map out how much this period is changed. And so but you can’t, if this is not a single measurement.

Nancy Chabot: In order to do that, they have to observe the asteroid over time, because the way that you map out the period is what’s called a light curve. That’s when the brightness changes. And right now that brightness changes every 11 hours in 55 minutes. So to map out what the new one is, you need to get a lot of measurements over an extended baseline, to be confident in how much you’ve changed it. So the telescopes will do that, but then the moon will come up, which you know, the moon has a lot of good redeeming features about it. But for ground-based astronomy, it kind of gets in the way sometimes.

Nancy Chabot: So you have to kind of wait those weeks, and then you get to go look again, and try to make some more measurements. And so it’ll really take actually, you know, maybe about a month, month and a half until we have a good measurement of how much we’ve deflected this asteroid. But the telescopes will actually be able to work until March of 2023, to look at this system. Again, this is why we’re targeting 2022 for the DART collision. So the telescopes here on Earth can make these fantastic measurements for many, many months, to measure this deflection very accurately.

Jim Green:So where’s the spacecraft now? And when is it going to launch?

Nancy Chabot:So the spacecraft is in California, it’s going to be launching from Vandenberg Space Force Base, and the launch period opens November 23. Pacific time. So the evening of November 23, on the California coast, 10:20pm.

Nancy Chabot:Hopefully, it’ll just go right then.

Jim Green:Wow.

Nancy Chabot: It’s got a really long launch period. And so it can actually extend into February. But we’re targeting November 23, and just ready to get into space.

Jim Green:That flexibility of launch period, is that because you actually have an ion engine on board of DART?

Nancy Chabot: Well, we do have an ion engine onboard DART. And we’re excited to be testing that out as a demonstration. But it actually has more to do with that DART never actually gets very far from Earth, because we’re going to this near Earth asteroid and we’re targeting this near Earth asteroid at the time when the distance between it and the Earth is minimized. And so DART sort of launches and just kind of stays pretty close to Earth the whole time. And so that that gives you a lot of flexibility in the launch window.

Jim Green:Well, that’s gonna be absolutely fantastic. But now that you’ve had experience with meteorites, is there any connection between Didymos or Dimorphos and the meteorites that you’ve studied?

Nancy Chabot:Yeah, I think it’s this is kind of fun to like, bring it full circle. So from spectral observations of Didymos that we’ve done with telescopes here on the Earth, we know that it’s linked to a meteorite type that’s called ordinary chondrites. And ordinary chondrites are some of these primitive building blocks of the planets. So they’ve got grains of metal next to grains of rock, and you can date these back to ages that are earlier than the planets. And so if that’s what the main moon Didymos is composed stuff, we don’t actually have any measurements for what the spectral type of Dimorphos, but from models of how binary asteroids form, they all predict that it should be the same material as Didymos. So this is, this is a fascinating type of meteorite, it’s actually the most common type of meteorite to hit the Earth. And then that makes it extra relevant for planetary defense, which is applied science, and you want to be doing this on the most relevant, appropriate common type of targets. So that makes these Dimorphos even more appropriate for this first planetary defense test.

Jim Green:Yeah, this is really exciting our ability for the first time to figure out ways that we may have to in the future, defend our planet. So all eyes are going to be on APL and what you guys are doing, to be able to start the process of helping the Earth survive in the long run. So thanks much, and I’m really looking forward to it.

Nancy Chabot:Thanks, I’m super looking forward to it too. And I think it’s really exciting that it, there’s a lot more for planetary defense yet to come to, I mean, you know, the follow on with the NEO Surveyor mission to find all the asteroids and get a dedicated space telescope up there. And then there’s the HERA mission, the European Space Agency is sending to the Didymos-Dimorphos system that will get there in 2026. And they’ll be able to see that crater made by darts and, and get the mass of Dimorphos and really characterize the system. And so DART with HERA will do more together than any one mission can combine on their own. And I think that’s really exciting for planetary defense, too, because it is, it is a global issue, it affects the entire planet. So working internationally and having that collaboration and having a whole team of doing this really makes it very rewarding.

Jim Green:Nancy, you know, I always like to ask my guests to tell me what was that event? person, place or thing that got them so excited about being the scientist they are today? And I call that event a gravity assist? So Nancy, what was your gravity assist?

Nancy Chabot:So when I was a kid, I really loved Star Wars. I thought Star Wars was amazing, was like the most amazing thing I had ever seen. And I used to, I really liked the story. But what I really liked about it was thinking about these different worlds and seeing them on the big screen, like worlds with two suns, and worlds made out of ice, and worlds where people lived in the clouds and asteroids with giant caverns. And I would ask my parents, how did they come up with all of this? And my parents told me at the time: They just dreamed it. And I used to go to bed at night and like, close my eyes and be like, tonight’s the night I’m going to dream like Star Wars that it’s gonna be amazing. I’d wake up in the morning like disappointed. My dreams were not that good. But I think that that sort of like wonder and fascination just really stuck with me. And you know, in some sort of way that maybe I haven’t fully realized. And, and now, I mean, I literally feel like I’m living the dream. I don’t have to close my eyes anymore. It’s like, I’m a part of this part of NASA’s exploration of the solar system to all these new worlds, and it’s just amazing.

Jim Green:And now you know that some of those dreams are coming true, where we’re finding planets that are orbiting two stars. And, and now you’re working with asteroids and deflecting them. So it’s, in a way, it’s a dream come true, Nancy.

Nancy Chabot:It indeed is, for sure.

Jim Green:Well, thanks so much for joining me and discussing your fantastic career and what you’re up to. I’m really looking forward to these missions,

Nancy Chabot:As am I, and everything else that comes after that as well. I mean, it’s just great to be part of all of these teams. That’s one of the things actually that I really like about this field as well is that it takes a lot of people to accomplish all of this. It’s way more than any one of us could do on our own. But together we’re doing these amazing things.

Jim Green: Indeed. Well, join me next time as we continue to journey to look under the hood at NASA and see how we do what we do. I’m Jim Green, and this is your Gravity Assist.


Lead producer: Elizabeth Landau

Audio engineer: Manny Cooper