NASA's Lucy reveals a tumbling, water-marked peanut asteroid
NASA's Lucy spacecraft flew past the small asteroid Donaldjohanson, and the full results are now out in the journal Science. The peanut-shaped rock tumbles on two axes and carries clay minerals that only form with water, hinting at a wet past. Scientists say it broke off a larger asteroid about 155 million years ago.
NASA's Lucy spacecraft flew past the small main-belt asteroid Donaldjohanson on April 20, 2025, and scientists have now published the full results in the journal Science. The bilobed, roughly half-mile-wide rock tumbles on two axes: end over end about every 10.5 days while wobbling around another axis about every 26.5 days. Lucy's infrared spectrometer detected iron-rich clay minerals that only form with liquid water, pointing to a wet past. The team, led by Simone Marchi at the Southwest Research Institute, says the asteroid likely broke off a larger water-rich body that shattered in a collision around 155 million years ago. The flyby was a rehearsal for Lucy's main mission to Jupiter's ancient Trojan asteroids.