watch NASA test its planetary defense system

We’ve seen the scenario played out in films numerous times: an asteroid is heading directly towards the earth and it’s up to a ragtag team of heroes to team up with NASA to save the planet. But forget Hollywood for a moment – today things get very real. NASA will test its asteroid planetary defense system, called DART, for the first time. Here’s what to know about it and how you can watch it.

• What is DART? DART is the name NASA has given to the first test of its asteroid planetary defense system. DART stands for Double Asteroid Redirection Test. 
• How does DART work? Dart is a spacecraft that NASA will intentionally slam into an asteroid. The spacecraft weighs 1,340 lbs. and is traveling at approximately 14,000 mph. The space agency wants to see if the resulting kinetic energy from the crash can change the asteroid’s trajectory just a little bit. 
• But why only change an incoming asteroid’s trajectory a little? Don’t we want to change it a lot? The goal is to change an incoming asteroid’s trajectory by a lot, ultimately. But if you can bump an asteroid that’s far out early enough, even a minute change in its trajectory at impact will eventually grow into a wide change as the asteroid continues its journey, thus missing earth.
• Can’t we just use nukes on an asteroid? We could, but because of how physics works, we probably don’t need such power to stop an incoming asteroid. As NASA is testing today, you just need something that could slam into an asteroid far enough out to bump it slightly off course, thus by the time it would reach earth, its path has been changed enough that it doesn’t come close to it.
• What asteroid is being hit today? It’s actually one of a pair that makes up a double asteroid. The big one is called Didymos, which is 2,560 feet in diameter. Didymos has a smaller asteroid orbiting it called Dimorphos, which is 530 feet in diameter. DART will slam into Dimorphos, and NASA will see if the impact changes Dimorphos’s orbit at all. If it does, it’s a good sign this type of planetary defense system can work.
• Is Didymos or Dimorphos a risk to earth? No, not at all. It’s just a good asteroid pair to test DART on.
• How can I watch the DART test? NASA’s coverage of the DART mission will begin at 6 p.m. ET/9 p.m. PT on its official YouTube live stream, embedded below. The actual DART impact is estimated to happen at 7:14 p.m. ET/ 10:14 p.m. PT.