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Flagstaff astronomers anticipate first-ever asteroid deflection test

A drawing of two asteroids against a field of stars. On approach is a square spacecraft with two solar panels.
NASA/Johns Hopkins APL/Steve Gribben
Illustration of NASA’s DART spacecraft and the Italian Space Agency’s (ASI) LICIACube prior to impact at the Didymos binary system.

NASA will attempt to strike an asteroid with a heavy spacecraft today. It’s an unprecedented test to see if it’s possible to deflect dangerous asteroids away from Earth. Astronomers on the ground in Flagstaff are standing by to help determine if the experiment is a success. KNAU’s Melissa Sevigny spoke with two of them, Cristina Thomas of Northern Arizona University and Nick Moskovitz of Lowell Observatory.

Tell me why NASA would want to smash a spacecraft into an asteroid to begin with?

Thomas: DART is really the first test of a kinetic impactor to deflect an asteroid off of its course. In theory if there was an object that was headed toward the Earth, you really just need a relatively small nudge, especially if you have a lot of time to prepare for that…. We want to test that out, so we understand exactly what’s happening should we need to apply it in the future.

Kinetic impactor, you just mean the motion of the spacecraft is what’s going to push this thing?

Thomas: Exactly, there are no bombs of any sort on board, which I think is a common misconception, that people think we’re going to make some sort of explosion, but no, we’re just going to hit the object with the spacecraft itself.

And tell me about the object that we’re targeting for this test?

Moskovitz: So the target of the DART mission is an asteroid called Didymos. Didymos is special in the asteroid world, because it’s what we call a binary asteroid, so Didymos it has a moon or a satellite that orbits around it. The spacecraft is aiming for the moon of Diymons, which has been named Dimorphous.

And this asteroid system is far away from us, it’s not actually headed in our direction?

Moskovitz: That’s absolutely right…. There’s no hazard associated with this experiment, it’s really just a test to see what happens when we hit an asteroid at really high speed.

How high speed are we talking?

Moskovitz: The impact will be spectacular. It’s a fairly massive spacecraft, something like, 500 kg or so, upwards of 1,000 lbs, and we’ll be hitting it at something like 14,000 mph.

Thomas: One of the common comparisons we have is the spacecraft itself is about the size of a vending machine, so it’s a really heavy vending machine with very long solar panels that’s going at very high speeds.

Both of you are involved with the ground-based efforts with this mission. Tell me how astronomers in Flagstaff are helping with the DART mission.

Moskovitz: The spacecraft is lost as the time of impact, so all follow up observations at least right after the impact will rely on ground-based telescopes. It’s sort of a two-part mission, where the engineers will get the spacecraft to impact, and then after that it falls to the observers like Cristina and myself to use telescopes on the ground and study the aftermath of the impact.

From the ground, all you can see is this tiny point of light. How can you tell if we successfully move the moon after we hit it?

Thomas: We understand the current orbit of Dimorphous around Didymos by observing what we call “mutual events.” It’s essentially when one of the objects, say the moon, goes behind or in front of the larger object. It’s essentially an eclipsing event, which is something that most people are relatively familiar with. When it does that, it blocks out a small portion of the light that the overall system sends our way…. You can kind of think of the Didymos system like a clock. You know, right now at least, before the impact, when to expect to see one of those eclipsing events. Afterward, we’re going to have to reassess when those events should happen. By looking at the timing, and the change of the timing relative to what we know now, that’s how we’re going to understand the orbital period change.

Moskovitz: This history of telescopic observations that we’ve been collecting of Didymos for 20 years now is really important, because it means we can pin down the location of Dimorphous to exquisite detail…. So the ground based observers across the globe that have done a phenomenal job of setting up this mission for success.

Now that the impact is imminent, how are you both feeling?

Thomas: I have to admit, I waver between feeling extremely good about the processes that we’ve set up and really nervous for no good reason, to be honest…. A lot of people spent many years on this, and the fact that it is now imminent is really mind blowing to me.

Moskovitz: I’m thrilled to be a part of this, it’s a really exciting mission. There are few missions that have such a singular moment associated with it. Everything culminates on September 26 at 4:14 Mountain Standard Time. We will know what our work looks like after that.

Nick, Cristina, thank you so much for joining me, and good luck.

Thank you.

The spacecraft will impact the moon of an asteroid at 4:14 Mountain Standard Time today. Lowell Observatory in Flagstaff is hosting an “Impact Party” this afternoon to celebrate the mission, including a live viewing of the impact on NASA TV. More details:

Melissa joined KNAU's team in 2015 to report on science, health, and the environment. Her work has appeared nationally on NPR and been featured on Science Friday. She grew up in Tucson, Arizona, where she fell in love with the ecology and geology of the Sonoran desert.
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