NASA Lucy reveals asteroid Donaldjohanson formed from a 155-million-year-old collision, wobbles in two directions, carries traces of ancient water
Asteroid Donaldjohanson is two rocks fused into one peanut shape, and NASA's Lucy probe found it carries traces of ancient water. It turns end-over-end every 10.5 days while rocking on its long axis every 26.5 days. The merger traces to a collision 155 million years ago. Publishe
NASA's Lucy spacecraft has pieced together the violent history of a small main-belt asteroid named Donaldjohanson, and the picture is stranger than expected. The object is not a single solid rock but two lobes joined at a narrow neck, a contact-binary shape that researchers say formed when fragments from an earlier collision drifted back together and merged under their own gravity. That collision is dated to roughly 155 million years ago. What sets Donaldjohanson apart is its motion. Rather than spinning cleanly on one axis, it tumbles end-over-end once every 10.5 days while also rocking back and forth around its long axis once every 26.5 days, a wobble in two directions at the same time. Researchers estimate it was spinning far faster soon after it formed, then slowed over tens of millions of years. Lucy's instruments also picked up traces of ancient water locked in the asteroid, a clue to the conditions in the early solar system. The findings were published in the journal Science. Lucy is now continuing toward its main targets, the Trojan asteroids that share Jupiter's orbit.