NASA scientists in the mission control room were on pins and needles. It had taken 10 months for their satellite to catch up with its target—a small asteroid called Dimorphos—and on September 26, the Double Asteroid Redirection Test (DART) spacecraft was finally within striking distance. Could the asteroid’s trajectory be permanently altered? This was the central question in humanity’s first test of “planetary defense,” a NASA initiative with a premise reminiscent of a Hollywood script: testing whether crashing a projectile into an earthbound asteroid could deflect it, thereby turning a direct hit to a near-miss.

A photo of the Dimorphos asteroid
Asteroid moonlet Dimorphos as seen by the NASA DART spacecraft 11 seconds before impact. DART’s onboard DRACO imager captured this image from a distance of 42 miles (68 kilometers). This image was the last to contain all of Dimorphos in the field of view. Dimorphos is roughly 525 feet (160 meters) in length. Dimorphos’ north is toward the top of the image. Photo courtesy of NASA/Johns Hopkins APL

Mind you, Dimorphos offered no such threat. Orbiting peacefully around a larger asteroid, Didymos, and located 7 million miles away (about 30 times the distance to the moon), it was never headed toward Earth like the fictional planet-killer Bruce Willis and crew destroyed in Armageddon—but NASA saw a chance to run a real-life test. At around 4 p.m. MST on Monday, DART’s camera spotted the small, gray-colored space rock, and within an hour, the spacecraft smashed into Dimorphos at more than 14,000 mph.

The hit was nearly a bullseye; the satellite reportedly struck the asteroid within 50 feet of its target center, and the kinetic force of that impact is expected to bring Dimorphos closer to the larger asteroid, Didymos, and shorten its orbit by about 1 percent—or about 10 minutes per revolution. In a live-streamed video, scientists and engineers at DART’s mission operations center in Laurel, Maryland, cheered and pumped their fists in celebration.

They weren’t alone. Jay McMahon, PhD, a participating scientist on the NASA DART mission, was also celebrating from Boulder, Colorado. In a conversation with 5280, the University of Colorado Boulder associate professor of aerospace engineering tells us what it was like working on the mission and what he’s looking for now that the DART satellite successfully collided with the asteroid.

Editor’s note: The following conversation has been edited for length and clarity.

A photo of DART scientist Jay McMahon, PhD.
DART scientist Jay McMahon, PhD. Photo courtesy of McMahon

5280: What was your role on the NASA DART mission and how long have you been involved with it?
Jay McMahon: I’ve been on the team for a year and a half now. Technically, I’m considered a participating scientist, and my role is to try to understand the effects of the impact in terms of the long-term evolution of the binary asteroid system—like over tens of thousands or hundreds of thousands of years. There’s a lot of complicated things going on with Didymos and Dimorphos orbiting each other, and that distance between them can either grow or shrink over time. One of the things that can affect the orbit is the shape of smaller orbiting body. And here, we just ran into the smaller asteroid and made a crater—or reshaped it somehow. I’m trying to predict how that will change the binary asteroid system based on what we did to the body.

Monday must have been a big day for you. Where did you watch the satellite’s final hours unfold, and what was going through your mind?
It’s a funny situation where it’s one of the few times in the history of space missions that you’re cheering when you know your spaceship died. It was great; we had a big watch party here at the aerospace engineering building at CU Boulder. We probably had a hundred people watching it: faculty members, lots of undergrad and graduate students, as well as a few local scientists from other institutions. It was fun and exciting—everyone was cheering and clapping at the end.

Were you nervous? Did you think there was a chance something could go wrong?
Well, I think it’s only natural, when you know you have one shot at something, that you’re going to be nervous until you know it worked. And there’s always some risk of failure because this stuff is really complicated and depends on everything going right. For example, the spacecraft was doing little maneuvers the whole time to keep re-centering the asteroid. So you might imagine that, if the thrusters stopped working, for example, then we could miss. But we had an awesome team that built a good spacecraft, and everything worked perfectly.

A photo of NASA's DART spacecraft launching in the dark.
The NASA DART Spacecraft Launches in World’s First Planetary Defense Test Mission. Photo courtesy of NASA/Johns Hopkins APL/Ed Whitman

As you said, intentionally crashing a spaceship into an asteroid is unusual. But so is a multimillion-dollar mission around “planetary defense.” Do you think that this was a worthy pursuit that could save our planet someday?
The hope is that we don’t have to. We—meaning NASA and other agencies—know where most of the large asteroids are, and we know their orbits well enough that we’re not concerned that they’ll run into Earth anytime soon, like over hundreds of years. But what we could be concerned about—even though there’s not an imminent danger of this—is smaller asteroids, which are harder to see and track. We’re not convinced we know where all of them are. So there could be an asteroid we face that’s way smaller than what killed the dinosaurs, but is still big enough that it could cause significant damage if we didn’t see it in time and do something about it. So that was the goal: to make sure that if that ever happens, we would be able to do something to protect ourselves.

In addition to being a working scientist, you’re also a professor at CU Boulder. Has your involvement on the DART mission given you a “cool” factor on campus?
Yeah! I think it’s always exciting for students to hear that the faculty members are doing real things other than just telling them facts. Because this is what they want to do: They want to work on real projects like this, which is why they’re in school to begin with. So when they feel like they can one day be involved in these types of missions, I think it’s really motivating for students.

Did anything about the mission surprise you at all?
One of the things that surprised me was how excited I was. I feel like we knew generally what was going to happen, having thought about it a lot. But the thrill of discovery, of seeing something new like these asteroids [up close] for the first time, was exciting. While the mission’s main goal was to prove planetary defense, we’re getting tons of new information about these binary asteroids—because we’ve never touched one like this before. Then of course, there’s all the pictures and videos we’re now getting from telescopes. And that’s the type of stuff we’re going to be poring over for weeks, to try and understand all that information, and figure out everything we can.

Chris Walker
Chris Walker
Chris writes for various sections of 5280 as well as