It Takes Time to Prepare
One of the primary reasons why it’s important for NASA to get the heads up of an asteroid’s trajectory is time. Johnson and his team need months and in some cases years to implement several plans to keep the space rock away. In other words, they don’t have unmanned ships ready to alter the course of the asteroids or Bruce Willis on speed dial to mine a hole to plant a bomb on the asteroid. So, the longer they’re aware of the problem, the more likely they are of finding a solution that will work.