This week, NASA launched a spacecraft on a mission to smash into an asteroid and test whether it would be possible to knock a speeding space rock off course if one were to threaten Earth. The DART spacecraft, short for Double Asteroid Redirection Test, lifted off from Vandenberg Space Force Base atop a SpaceX Falcon 9 rocket in a $330 million project with echoes of the Bruce Willis movie “Armageddon.” It’s the stuff of Hollywood movies, but the threat to Earth by hazardous asteroids is rooted in fact, not fiction. “We look at the moon, we look at the Earth, we see that it’s full of craters. More on the Moon than on the Earth, which is, of course, telling us that impacts of small bodies on Earth on geologic time scales are normal,” says Thomas Zurbuchen, associate administrator for science at NASA. If all goes well, the boxy, 1,200-pound …