If all goes well, the spacecraft that NASA plans to launch Tuesday will smash itself to bits against an asteroid.
If all goes absolutely perfectly, that impact will jostle the asteroid into a slightly different orbit, meaning that for the first time, humans will have changed the trajectory of a celestial object.
Making history, however, is incidental. The real mission is to defend the planet.
No need to panic: The target space rock has no chance of striking Earth, nor does any other known asteroid for at least half a century. This NASA mission, operated by the Johns Hopkins University Applied Physics Laboratory in Laurel, Md., is testing a technique for redirecting an asteroid in case future Earth folk really need to bat one out of the way.