An Earth-bound asteroid wouldn’t have to be huge to be a problem. Even something just a couple of hundred feet across could cause widespread devastation if it hit a town or city.
For the objects we can track (and plenty slip by without our realizing until too late), scientists estimate their trajectories and calculate the probability of a collision. We’ve been lucky so far, because we’ve not yet had to deal with a scenario where a space rock is on a crash course for Earth. If one were, we might have a shot at deflecting it onto a safer path—but we’ve never tried anything like that before.
That will soon change. Just last week, more than 130 scientists met in Rome to hash out more details about an informal collaboration between NASA and the European Space Agency (ESA) called AIDA, short for “asteroid impact and deflection assessment.” AIDA refers to a pair of missions designed to slam a spacecraft into a near-Earth asteroid and then study the impact to see how feasible it might be for humans to push an asteroid off its trajectory, should we ever need to.