building, the burj khalifa in dubai, an target its secondary body and moonlit called dimorphose 525 feet wide. scientists will study smaller asteroid orbiting the larger didymos to see how much it changes course when d.r.a.t. hits this fall. this one is pretty cool, ten months and we re going to rendezvous and hit this and put some english into it. reporter: while none are headed our way, they still want to be ready. may we all see these events through with the courage worthy of this challenge. reporter: tonight, all eyes on the mission that could one day save planet earth. morgan chesky, nbc news. let s hope it works. we have a vested interest in that that s nightly news for this tuesday thanks for watching. i m lester holt. please take care of yourself and each other. good night