Lab Notes: Why did NASA spend a billion bucks on Lucy?

Somewhere out past Mars in the early hours of Easter Monday, a space probe called Lucy whizzed by an asteroid named Donaldjohanson. Lucy then sent back images showing Donaldjohanson is about five kilometres wide and shaped like a peanut. It's one of a handful of asteroids on Lucy's 12-year itinerary. So what does the billion-dollar mission hope to achieve?