A rotating mosaic of asteroid Bennu, composed of images captured by NASA's Osiris-Rex spacecraft over a four-hour period on December 2, 2018. NASA/Goddard/University of Arizona NASA's Osiris-Rex spacecraft briefly landed on an asteroid called Bennu on Tuesday to collect samples of its rock. But now a valve on the probe's sample-collecting arm won't close, and the bits of asteroid it grabbed are floating away. The team is frantically trying to store the asteroid dust in a safer place before they lose much more.