Asteroids are always moving in space, but what do we do if one of these giant space rocks heads straight for Earth? Scientists don't worry about asteroids unless, on extremely rare occasions, an asteroid gets within 28 million miles of the Earth's atmosphere. NASA's Double Asteroid Redirection Test (DART) offers a new defense system to keep asteroids away. Using a process called kinetic impact, DART literally knocks asteroids into another orbit. Find out how DART passed its first test and how it can help defend the Earth.