Tonight, NASA's DART will slam into an asteroid at 24,000 kph

Tonight, if all goes well, NASA’s Double Asteroid Redirection Test — or DART — mission will slam into a tiny asteroid moon at nearly 24,000 kilometers per hour, blasting out a cloud of debris, creating a flash of light visible across the solar system, and changing the velocity of the asteroid by less than a millimeter per second… which is tiny, but significant.