Asteroid Bennu's Surface Mystery Solved by XCT Scans

X-ray computed tomography (XCT) scans of asteroid Bennu samples, released on March 17, 2026, have revealed common types of crack networks within the samples. These findings resolved a long-standing mystery regarding the asteroid's surface.

The Surface Anomaly

Upon its arrival at asteroid Bennu in 2018, NASA's OSIRIS-REx spacecraft observed a surface covered in boulders. This observation was at odds with 2007 data from NASA's Spitzer Space Telescope, which indicated low thermal inertia. Low thermal inertia is typically associated with surfaces that heat up and cool down quickly, similar to a sandy beach, rather than boulder-rich terrains that would retain heat for longer periods.

"Bennu's surface, visibly covered in boulders, paradoxically displayed thermal properties akin to a sandy beach."

Cracks and Porosity: The Resolution

Data collected by OSIRIS-REx during its survey suggested that the boulders might be more porous than anticipated. Investigations of the samples on Earth using XCT scans confirmed this possibility, showing that the crack networks contribute to the boulders' high porosity. This characteristic allows the boulders to heat and cool rapidly, thus reconciling the discrepancy between the visible boulder-covered surface and the thermal inertia measurements.