The target they have chosen is the asteroid Didymos B, roughly 160 meters in diameter, one half of a binary asteroid system. Didymos B orbits the larger asteroid Didymos A every 11.92 hours and this will help determine the ultimate success (or failure) of the mission.
The Didymos system is classified as a Near-Earth Object (NEO), meaning it’s close but not too close that it might hit us, making it the perfect test subject to flex our anti-meteor might.
The mission is set to launch in July 2021, with the impact expected in September 2022.
A cubesat called LICIAcube will detach from the DART craft just before impact and beam photos of the impact back to Earth for analysis, so we’ll have front row seats to see whether we’re doomed or not.
The ESA’s Hera observation spacecraft will launch in 2023 and take observations starting in 2027 to give the final appraisal of the mission.