Short Wave - DART: The Impacts Of Slamming A Spacecraft Into An Asteroid

Episode Date: December 9, 2022

If an asteroid were hurling through space, making a beeline straight to Earth, how would humans prevent it from doing what it did to the dinosaurs? Would we bomb it? Would we shoot lasers at it like a scene from Hollywood's latest sci-fi flick? Well, the folks at NASA have designed and tested a theory."The DART mission, the Double Asteroid Redirection Test, is essentially our first test of a kinetic impact for planetary defense." says Cristina Thomas, assistant professor of Astronomy and Planetary Science at Northern Arizona University. Put simply, scientists at NASA took a spacecraft and crashed it into an asteroid — hoping the little nudge, like bumper cars, would be enough to push the asteroid off course. Today on the show, Short Wave's scientist-in-residence Regina G. Barber talks to Cristina Thomas about what it was like watching the success of the DART mission and what this means for science and planetary defense. Email Short Wave at [e-mail]. Or, follow us on Twitter at @NPRShortWave.See pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences.NPR Privacy Policy

You're listening to Shortwave from NPR. When they first told us that they were approving this mission and we were going to fly and impact this asteroid, you know, I almost did a double take. I was kind of like, there's no way they're going to let us do this. This sounds too fun. That's Christina Thomas, assistant professor of astronomy and planetary science at Northern Arizona University. She leads the observations working group for the DART mission. They're studying how the asteroid's movements will change after impact.

NASA sent a spacecraft to slam into an asteroid millions of miles away at a breezy speed of 14,000 miles per hour. The goal was to see if humans could do this and whether it could successfully change the orbit of this smaller asteroid or moonlit as it rotated around the larger asteroid. We did this, like this worked. In a world where giant asteroids change the fate of Earth. All right.

That's enough of that. But Christina knows all about these deep impacts. I'm sorry. I couldn't help myself. So what happened to the dinosaurs is about 65 million years ago, a very large object, you know, came in and impacted the planet. And the crater is actually just around the Yucatan Peninsula in Mexico. So if an object that size were to come towards Earth now, is NASA's dart technology enough to divert it? Well, no.

It's okay. Don't panic. There's a huge caveat there that we know that's not going to happen. So, you know, one of the great things about the current planetary defense strategy is that we understand that there's more than one component. And one of the largest components is discovery. So we have to understand where all the objects are, what their orbits are. And we know that those dinosaur killer-sized asteroids, we know where they are and we know their trajectories do not come close to the planet. Well, that's a relief.

Today on the show, we Earthlings hit an asteroid and actually change its orbit. What's it like watching the success of the DART mission and what impacts? You're welcome. This has had on science. I'm Regina Barber, and you're listening to Shortwave, the Daily Science podcast from NPR. Okay, I need to pull up real quick my favorite video from the interwebs. It's the DART mission hitting the asteroid like the world's most awesome pool shot. I had to show it to Christina Thomas for a little nostalgia.

And that ejecta that shoots off upon impact, that's my favorite detail. I love that poof. Do you see it? I do, yeah. Like it was on everywhere. It was on all, it was all over the place. People were sharing this image of actually seeing the collision. Tell us how it was from your point of view. The impact event, you know, I'm standing there with a bunch of my colleagues at the Planteau Defense Coordination Office.

And, you know, my phone starts, you know, just lighting up with these images. I could think of at least four different videos that I got from different observatories of that poof that happened right after. And every time I saw it, it was no less mind-blowing. Like, it was just really truly fantastic to see because we knew that things were going to happen. Like, this wasn't unexpected, but it was still just like, whoa, we did it. And there's this kind of moment of pure awe. Well, and it's not only a success like scientifically, but it's a success with like, like, public engagement.

I think that this taps into a little bit of people's nostalgia for science fiction, something that's just a little bit out of the ordinary. That just seems a little bit out of the box, I guess. We started observing the Didomo system in 2015, and all of the observations up until the moment of impact were to better understand exactly what the orbital property. of the system were before we changed it. This mission is almost like a sci-fi movie plot, but in real life. So can you, like, kind of back up for a second and can you give us an outline of what the

DART mission was trying to do? Right. So, you know, the DART mission, the double asteroid redirection test, is essentially our first test of a kinetic impact for planetary defense. And that's a very specific way of saying that we needed to think about how we would move an asteroid should the trajectory of that asteroid be coming close to Earth and be a threat to impact us. The best idea is a kinetic impact. And so that's essentially taking one spacecraft like dart and directly impacting it into another

and using the momentum behind that impact to change the trajectory of the asteroid. And so we say it this way specifically because there's no additional explosion, there's no explosives on board the spacecraft. It's just the momentum of the spacecraft itself. There's no bombs. Exactly. It's just the spacecraft pushing it. And we knew that when we had the spacecraft impact, there was also going to be the ejector, the material that comes off. And that's going to give it a little extra push too. And so one of the reasons to do this test is that it's actually more complicated than people might think.

I mean, you teach physics, right? So you know that we always talk about like pool balls, right? Like one pool ball hits the other pool ball. But you're talking about if one of the pool balls like chunks of it fell off, right? And it wasn't such a nice collision, right? Right, right. And then those chunks had momentum that, you know, pushed it forward. Yeah, exactly.

Yeah. And so a lot of folks thought about this very carefully. And we realized that if it was just a simple billiard ball experiment, one object hitting another, then we'd have a period change that was probably going to be something like seven minutes from the initial orbital period of demorphose. And that's not at all what we found. So for our listeners, can you describe the system, just kind of break down what the system looks like with the satellite? And then what was the orbit beforehand? Right. So the two objects in the system are didemos, which we call the primary because it's the

larger one, and demorphose, which is the satellite or the moonlit of didemos. And so those two objects are going around the sun together. And at the same time, demorphos is orbiting didemos. And the initial orbital period that we calculated before the impact was about 11 hours and 55 minutes. Yeah. And so that's really what we were starting with. And we wanted to understand exactly how that was going to change. We impacted in a head-on collision. So, you know, we were coming towards the front-facing side of demorphos, and by doing that, we knew that we were going to change the system in such a way that we were going to decrease the orbital period. And so we were trying to figure out exactly how much we decreased it.

Demorphos, the moonlit, orbiting didimos, now has an orbit that is 32 minutes shorter. But, Christina, the sci-fi piece and why so many people are covering this so closely is the possibility of, like, future impacts. and the fears associated with that. We know that several asteroid impacts happened in our history, the one that killed the dinosaurs, the one that created the moon. What can you tell us about that? I mean, I think right now we're scared of the fact that we know that it's happened

and that we don't know if it will happen again. And also, you know, 90s action movies. We're scared of those. You know, people are fascinated by dinosaurs. So what did happen to those dinosaurs? help us out here. Right. So what happened to the dinosaurs is about 65 million years ago, a very large object, you know, came in and impacted the planet. And the crater is actually just around the Yucatan Peninsula in Mexico. And so we were able to discover through a variety of

different things that put all these pieces together. But, you know, number one, there's a very interesting layer of material at the boundary between where the dinosaurs existed and when they no longer were present on the planet. And so we call that the KT boundary. It's enriched in things that we don't find on Earth, that we find on other bodies, on meteorites specifically, and asteroids. And so we can use that to start to connect that something had happened and something had been introduced from outer space. And then eventually there was actually a survey for the oil company in Mexico looking around the Gulf of Mexico and they stumbled onto the impact crater itself. and we were able to really connect all of these pieces of the puzzle.

And so it's really, really a great story because it's something that is actually somewhat modern and has really been developing over time and more and more details come to light. So we have to understand where all the objects are, what their orbits are, and we know that those dinosaur killer-sized asteroids, we know where they are and we know their trajectories do not come close to the planet. So what other governments do we as the U.S. work with or does the mission work with so that we can like alert each other or talk to each other so that we can like kind of protect the whole planet? I mean, there's actually a lot of initiatives. And so, you know, the U.S. is part of Iwan, the International Asteroid Warning Network. And so that's a group of folks that really tried to coordinate a lot of different things. And NASA's Planetary Defense Coordination Office actually is part of that effort and part of many other efforts that we have. on the coordination side as well.

For the DART team, and especially for the Observations Working Group, it's been very interesting because we have an extremely international group of collaborators. In fact, we have taken observations on all seven continents since the time of impact. And it's been really truly exciting to see so many people interested in this specific endeavor. Why did you pick this target? Like, why did DART pick this target? There's several reasons why we pick this specific target. And so one of them is that the demorphose system is what we call an eclipsing binary,

which means that from the planet, the moon goes in front of and behind the larger one. So demorphos comes in front of Didemos and it goes behind Didimos. And when it does that, because of the geometry of how we are with respect to the sun, it's casting shadows or blocking out the light directly. And so we're going through eclipses and occultations. And that is something that we can actually observe from the ground. But, you know, demorphose is actually very important from a planetary defense perspective. It's in a key size range.

It's a little bit larger, but we have a congressional mandate that we're supposed to discover as a community over 90% of the 140-meter diameter objects. And, you know, demorphos is about 160 meters. Oh, wow. You know, it's a very key size range. That's something that we should understand because that is something that could cause regional devastation. This is not, you know, a complete catastrophe. But it's also something that we have only discovered 40% of the objects in that size range. And so we really need to do better.

So right now we are seeing about 40% of those asteroids that are, like you said, bigger than 100 meters. And then you want to kind of be able to get 90% of, how many asteroids we pretty much know are out there. How do you close that gap then? How do you go from 40% to 90%? I mean, there's a few ways that we're trying to do that. And part of that is being smart about how we survey and which telescopes we used to survey. You know, and so we are, you know, we have a lot of ground-based telescopes that that is their job.

They survey the sky for new asteroids with an emphasis on near-Earth asteroids. We also have a couple of things coming up in the near future. the Rubin Observatory, which is in Chile, should start observations in the coming years. And one of the things that they are doing as part of that is doing a cadence to discover more asteroids. And so we think that they're also going to find a lot of objects. The Planetary Defense Coordination Office at NASA is so interested in planetary defense overall strategy. We have a follow-up mission that comes out of that office, and that's called NEO Surveyor. But the idea is that this would be a space-based telescope using near-infrared wavelengths, which is really good because near-earth objects are kind of warm.

And we want to use that to discover even more objects. So if this was a sci-fi movie, like in your mind, Christina, is the first art mission like a climax of that sci-fi movie or is it just the beginning? I think that it's like the end of the first act. but I think we've really set the stage for a lot of other exciting things to come. Thank you, Christina. That was amazing. Thank you for talking to us. Truly a pleasure. I really like talking about DART. It's been a great time. This episode was produced by Devin Schwartz, edited by Gizal Grayson, and fact-checked by Abbey Levine. Gilly Moon was the audio engineer.

Brendan Crump is our podcast coordinator. Beth Donovan is our senior director, and Anya Grunman is our senior vice president of programming. I'm Regina Barber. Thanks for listening to Shortwave, the Daily Science podcast from NPR.