Next month NASA's Lucy probe will visit an asteroid that's been waiting 150 million years to say hello

A spacecraft with two round solar panel wings on either side of it. In the background, there are two asteroids. The one on the right is bigger than the one on the left.

The next stop for NASA's asteroid-hopping spacecraft Lucy is a space rock named Donaldjohanson, an object researchers recently learned is about 150 million years old.

Lucy will fly past the three-mile-wide (five-kilometer-wide) asteroid on April 20, but the trip mostly serves as a rehearsal for other asteroid encounters down the road — namely, Lucy's final destination: Jupiter's Trojan asteroids. Over a 12-year mission, Lucy is scheduled to visit a total of 11 asteroids across two swarms that are leading and trailing Jupiter.