WHY A NASA SPACECRAFT WILL CRASH INTO AN ASTEROID

In the first-of-its-kind, save-the-world experiment, NASA is about to clobber a small, harmless asteroid millions of miles away.

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A spacecraft named Dart will zero in on the asteroid Monday, intent on slamming it head-on at 14,000 mph (22,500 kph). The impact should be just enough to nudge the asteroid into a slightly tighter orbit around its companion space rock — demonstrating that if a killer asteroid ever heads our way, we’d stand a fighting chance of diverting it.

Cameras and telescopes will watch the crash, but it will take months to find out if it actually changed the orbit. The $325 million planetary defense test began with Dart’s launch last fall.

ASTEROID TARGET

The asteroid with the bull’s eye on it is Dimorphos, about 7 million miles (9.6 million kilometers) from Earth. It is actually the puny sidekick of a 2,500-foot (780-meter) asteroid named Didymos, Greek for twin. Discovered in 1996, Didymos is spinning so fast that scientists believe it flung off material that eventually formed a moonlet. Dimorphos — roughly 525 feet (160 meters) across — orbits its parent body at a distance of less than a mile (1.2 kilometers).