The series of events that brought us to this particular point in human history can be traced back to 1998, when an astronomy institute issued an alert about a recently discovered asteroid that looked like it could hit in 2028. In astronomy time, that’s basically tomorrow, so if the asteroid was indeed a threat, we needed to do something about it soon. Scientists at NASA quickly found that this rock wasn’t going to collide with Earth, but the agency did establish a center devoted to estimating the probability of asteroids and comets hitting Earth, so that we might have a chance at actually stopping them.

The DART mission is aiming for Dimorphos, a half-mile-wide asteroid that orbits a bigger asteroid, Didymos, like a moon. If the mission works as intended, DART will carve a crater into the surface of Dimorphos and fling out a bunch of rocky debris, known as ejecta, explains Angela Stickle, a planetary scientist at the John Hopkins University Applied Physics Laboratory who leads the team that does impact simulations. “As that ejecta leaves the asteroid, it acts kind of like a rocket engine and pushes the asteroid,” Stickle told me. “You’re creating sort of a natural engine on the asteroid that then slows down its velocity.” Stickle and her team predict that the impact will shrink Dimorphos’s 12-hour orbit by about 10 minutes or so. A change in an object’s velocity translates into a change in its orbital path; if an asteroid were heading toward Earth, a version of this technique might shift an asteroid’s trajectory enough to turn a certain disaster into a near miss.