Why is a NASA spacecraft crashing into an asteroid?

CAPE CANAVERAL, Fla. (AP) — A NASA spacecraft is about to clobber a small, harmless asteroid millions of miles away. The spacecraft named Dart will zero in on the asteroid Monday, intent on slamming it head-on at 14,000 mph. The impact should be just enough to nudge the asteroid into a slightly tighter orbit around its companion space rock. It’s the first save-the-world experiment of its kind. If successful, the test will demonstrate that if a killer asteroid ever heads our way, we’ll stand a fighting chance. Dart blasted off on the $325 million mission last fall.