CAPE CANAVERAL, Fla.—A NASA spacecraft named Lucy rocketed into the sky with diamonds Saturday morning on a 12-year quest to explore eight asteroids. Seven of the mysterious space rocks are among swarms of asteroids sharing Jupiter’s orbit, thought to be the pristine leftovers of planetary formation. An Atlas V rocket blasted off before dawn, sending Lucy on a roundabout journey spanning nearly 4 billion miles. Researchers grew emotional describing the successful launch—lead scientist Hal Levison said it was like witnessing the birth of a child. “Go Lucy!” he urged. Lucy is named after the 3.2 million-year-old skeletal remains of a human ancestor found in Ethiopia nearly a half-century ago. That discovery got its name from the 1967 Beatles song “Lucy in the Sky with Diamonds,” prompting NASA to send the spacecraft soaring with band members’ lyrics and other luminaries’ words of wisdom imprinted on a plaque. The spacecraft also carried …