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NASA spacecraft will collide with asteroid in planetary defense test

A drawing of a spacecraft with a square body and two wing-like solar panels headed for a lumpy-shaped rock orbiting around a bigger asteroid.
NASA/Johns Hopkins, APL/Steve Gribben
Illustration of the DART mission

NASA plans to launch a spacecraft tonight that's meant to collide with a small moon orbiting an asteroid and try to change its orbit. The DART mission or Double Asteroid Redirection Test is a practice run in case an asteroid ever sets a collision course with Earth. KNAU's Melissa Sevigny spoke with one of the scientists involved with the mission, Cristina Thomas of Northern Arizona University.

I’m not sure a lot of people think of asteroids as having moons. So it’s an asteroid with a little moon going around it, and you’re actually going to smash into the moon and try to change the moon’s trajectory.  

Exactly, so we’re smashing into the much smaller moon.

So this is a little unusual because NASA usually tries to avoid smashing into things when they send a spacecraft to space. What’s going to happen to the spacecraft?

This spacecraft itself is going to be destroyed…. One of the exciting things is, though, that we have a partnership with the Italian Space Agency who are providing a CubeSat which is called LICIACube … and they will be kind of trailing along, and will take images of the impact itself and the evolution of the ejecta and things like that, so that we can study what happened during impact….The great part from my perspective is that ground-based observations from telescopes is going to be really useful for understanding exactly how successful the impact was.

You’ve been studying this asteroid or this binary system from the ground for a while now. Tell me what do we know about this particular asteroid and its moon by studying it from the ground?

In 2003 we learned that this was actually a binary asteroid. The primary one, the larger body, is called Didymos, the moon itself is called Dimorphos…. We use a technique which is called light curve photometry. This is really just looking at how the brightness of the system—the two bodies together—how the brightness of that system changes over time…. It gets a little bit dimmer when the moon goes in front of or behind Didymos, because you have a little bit less light. We’re using that essentially to think of Didymos almost as a clock. We know exactly how long it takes for it to come back around… and then once we impact, we’re going to do very similar observations to see what the new orbital period is so we can understand how it changed.

9:46 How big of a rock are we talking about, that you’re smashing into?

Dimorphos is in the sweet spot for studying asteroid impacts in general. It’s about 150 meters in diameter, so 150 meters across. This is something that’s not particularly large, it’s not something that would be associated with a large impact, the size that people are thinking about with dinosaurs killers and stuff like that. But it is one of the spots that is still important to understand, because that would in fact reach the surface and cause issues for people in the surrounding area. And also, is in one of the spots where it’s harder to detect these objects. We’re really, really good at detecting the larger objects because they’re brighter and easier to see with our telescopes, but some of the ones that are more in this size range is when we start to have less favorable statistics.

We’ve all seen blockbuster movies that do this scenario and have an asteroid headed to Earth, but in real life, how much do people need to worry about this?

One of the interesting things to note, the larger ones we think of disaster scenarios, we’ve discovered the vast majority of those, well over 90 percent. Once we discover them, then we can understand their orbits and determine whether or not they’re hazardous to the objects… It’s going to become things like that much smaller objects, again, they’re hard to discover because they’re much fainter… We have to worry about these mid-range objects, and that’s really where the kinetic impactor is going to be a great test, that’s the sweet spot for that specific type of experiment…. It’s exciting to take the specific expertise I have, and that a lot of my collaborators have, and apply it to such a broad, interesting, exciting problem. And of course, it’s really exciting to be involved in the first of anything, and being involved with the first kinetic impactor experiment is going to be a really interesting time.

Cristina Thomas, thank you for speaking with me.

Thank you.

Tonight is the first possible launch window for the mission; the attempt will be made at 11:20pm Arizona time. Live coverage will be shown on NASA Television, the NASA app, and the agency’s website. The spacecraft will arrive at its destination in September or October 2022.