NASA researchers say they have finally solved a long-standing puzzle about asteroid Bennu: why it cools off so rapidly even though its surface is covered in huge boulders. The answer, they report, lies not in the boulders' exteriors but deep inside them.
Samples brought back to Earth revealed that Bennu's rocks are filled with microscopic cracks. These hidden fractures create porosity that allows heat to escape more readily, acting as a kind of thermal shortcut that explains the unexpectedly fast heat loss observed from orbit.
The finding settles a mystery that had puzzled scientists since spacecraft data first showed Bennu's surface temperatures dropping quickly after sunset. With the returned samples, the team could directly inspect the rock structure and tie those remote observations to physical evidence, giving a clearer picture of the asteroid's makeup and behavior.