The DART Asteroid Impact Mission: It’s A Cosmic Smash

JOHN DANKOSKY: This is Science Friday. I’m John Dankosky. Earlier this week, we saw some amazing images coming from a vending machine-sized spacecraft as it hurtled intentionally into an asteroid. It was called the DART mission, for Double Asteroid Redirection Test, trying to see if a small impact caused by humans could be enough to change the path of some future asteroid on a collision course with Earth.

Joining me now to talk about the mission and how it went is Nancy Chabot. She’s the DART coordination lead and a planetary scientist at Johns Hopkins Applied Physics Laboratory. Welcome to Science Friday, Nancy.

NANCY CHABOT: Oh, thanks for having me. It’s been an exciting week, and glad to be here.

JOHN DANKOSKY: Yeah, it has been an exciting week. So how do you think everything went?

NANCY CHABOT: Everything was a smashing success. I mean–

[LAUGHTER]

I think that’s the words to use for the day. Yeah, I mean people have worked on this for years. NASA started funding this back in 2015 here at the Johns Hopkins Applied Physics Lab. But really, it was an idea that the international community wanted to do even before this. And it’s just such an exciting day that now we’ve taken this first step and we’re getting all this great data rolling in and trying to take this next phase of, OK, what did this mean for how effective might this be in the future for deflecting asteroids if we needed it?

JOHN DANKOSKY: How hard was this to do? I mean, how much precision did it take to hit this little tiny moon asteroid so far out in space?

NANCY CHABOT: Yeah, and you left out the part where we had never seen what it looked like before. So–

[LAUGHTER]

JOHN DANKOSKY: Oh, there’s that.

NANCY CHABOT: If you just want to add to the complexity there, right? Yeah, so you are targeting a small asteroid in space that had never been seen before. So you weren’t sure of its shape. You had some general idea of the size, but the specifics of how it would be lit by the sun, all of that was unknown. And you need to target it at very high speed, right, in order to have a measurable deflection.

So you’re going at 14,000 miles per hour towards an object that you’ve never seen before. It’s right next to another asteroid, Didymos, that’s brighter and larger. And so you can’t actually tell the difference between Dimorphos and Didymos until within the last hour of the mission.

And so they had to make the spacecraft smart. And that’s where they developed SMART Nav, the set of algorithms that uses the camera images on board and interpreted those images, interpreted which one was Didymos and Dimorphos, fired each of the little thrusters just the right way. And all of this happened while it was 7 million miles away from the Earth.

The spacecraft was fundamentally operating on SMART Nav, flying itself, steering itself in order to do that collision. And those images were fabulous to see here on the Earth and are really giving us a lot of good science that we’re doing to understand these asteroids. But they were crucial in order for using that system on board in order to find that asteroid and target it.

JOHN DANKOSKY: When it gets closer, the asteroid kind of looks like just a big pile of rubble, like a gravel pit hurtling through space. Is that what you expected it to look like?

NANCY CHABOT: I think we all had different expectations. But yeah, from other asteroids that we’ve seen, sort of a big pile of rocks is sort of what they are. We shouldn’t think of them as these one solid chunks of material, necessarily. They seem to be loosely bound together boulders and smaller rocks and pebbles, all of different sizes, kind of just thrown on there all together. And so when we did see that, that’s sort of like, wow, OK, I guess this is maybe what makes up asteroids.

One thing that’s interesting scientifically, also, is that Dimorphos is actually the smallest asteroid that’s ever been visited by a spacecraft. So we had seen these other asteroids, and we had seen they kind of looked like piles of rock. And we’re like, but maybe once you get smaller, they won’t just be piles of rock. Well, this one still looks like a big pile of rocks.

So that’s kind of moving the bar from what we understand about asteroids already, just those images that were shared and everybody experienced at the same time for understanding what these smaller-sized objects look like, which is important for planetary defense because these are the sorts of objects– there’s more of them out there– this is the population that’s a priority for NASA to find, these few-hundred-meter-sized objects. But it’s also interesting scientifically to understand what this smaller size of asteroid looks like, and what does that mean for how things evolve in the solar system.

JOHN DANKOSKY: So as you’ve said, the big idea of this mission is to see if you can move the path of an asteroid like this so that you can provide some planetary defense. Do we know yet from the data how well that part of the mission worked?

NANCY CHABOT: So how much did we move the asteroid? We’re still working on that. But it’s also this data of how much material was ejected off the surface is an important component because that’s essentially a lot of the unknown. We knew what the mass of the spacecraft is. We knew the velocity we were coming in with. We could sort of understand what momentum we would transfer based on that.

But we’re getting this extra push we expect because of all of this material ejected off the surface, like a little rocket engine that’s really enhancing the deflection. Now, how much? That’s where we are. Actively going on, still getting that data and still trying to figure it out.

JOHN DANKOSKY: Yeah. So this mission, of course, took quite a bit of time and planning to pull off. How much advance warning would you need to pull off something like this if there was a threat? I mean, in the movies, we’d hear President Morgan Freeman say, you have 24 hours, and somehow or other, everything would rally. I mean, what would you really need to get up there and use this in a way that could, if we needed to, save the Earth?

NANCY CHABOT: Yeah, I think this– I actually really kind of love fun movies, so I’m not trying to throw any shade out there. But we’re trying to create this different reality where we’re not finding these things at the last minute. So if you find the asteroids, and once we have them and we’re tracking them, people can understand where they are for, like, 50, 100 years. This is completely reasonable.

So if we find the asteroids, we can very realistically be in a position where we’re assessing if they’re a threat to the Earth and having decades, potentially, in order to do something about it. And that’s what you would want, right? It’s not going to make for a very fancy movie, but it’s a reality that we could realize. And something like DART, then, would be realistic, where you would do this many years in advance. And it would be this small collision that would add up to a bigger change in its position with time and a disaster averted without a bunch of fanfare or anything.

JOHN DANKOSKY: A last thing for you– people who work on space missions like this, many of them have long-term goals, like a deep space probe that you can imagine hurtling out into space for millions of years and maybe being found by some civilization a long time from now or a Mars Rover that is giving us wonderful data for decades to come. This project was essentially, we’re going to build this really cool thing, and we’re going to crash it, and we’ll never see it again. And I guess I’m just wondering, as someone who helped to make that happen, how you feel about that.

NANCY CHABOT: Oh, well, I think all of us here at Johns Hopkins Applied Physics Lab, especially people here designed that, right? They built it. And a lot of people like to think of it as, oh, they must be really attached to it.

And in some ways, it’s like you built this so it could have its moment, right? I mean, this was why you did it, so it could have this moment of glory and do what it was designed to do. You know, you’re really looking at thousands of people over years. And I think everybody is proud of the DART spacecraft.

JOHN DANKOSKY: Well, congratulations on this amazing effort. Nancy Chabot is the DART coordination lead and a planetary scientist at Johns Hopkins Applied Physics Laboratory. Thank you so much for joining us.

NANCY CHABOT: Oh, thank you for having me.

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